Posted online October 3, 2005
The species distribution of Cereal Cyst Nematode in rainfed wheat production systems of Turkey and Syria using conventional and molecular tools. H. Abidou (1), J. M. NICOL (2), N. Bolat (3), R. Rivoal (4), and A. Yahyaoui (5). (1) Faculty of Agriculture, Aleppo University, Aleppo, Syria; (2) International Maize and Wheat Improvement Center (CIMMYT), Ankara, Turkey; (3) Anadolu Agricultural Research Institute, Eskisehir, Turkey; (4) INRA/AGROCAMPUS, Rennes, Le Rheu, France; (5) International Center for Agricultural Research in the Dry Areas (ICARDA), Aleppo, Syria.
The Cereal Cyst Nematode Heterodera avenae is economically important worldwide in rainfed wheat production systems. A survey of 80 wheat and 63 barley fields between 2000-2003 in Turkey and Syria indicated the widespread distribution of cyst nematodes with 80% of cereal fields in Turkey and 63.8% and 77.8% of wheat and barley fields in Syria. Based on conventional morphometrics and supported by PCR-RFLP analysis of samples indicated H. filipjevi and H. latipons were widely distributed in Turkey, whilst Heterodera latipons was the most dominant species in Syria, followed by H. filipjevi and 1 sample of H. avenae. More work is necessary to establish the agroeoclogy related to the distribution of cyst species and their economic importance in the region.
Etiology, survival, and management of powdery mildews of stone fruit in California. J. E. ADASKAVEG (1), H. Förster (2), R. Duncan (3), and W. D. Gubler (2). Dept. of Plant Pathology, University of California, (1) Riverside, CA 92521; (2) Davis, CA 95616; and (3) UCCE, Stanislaus Co., Modesto, CA 95358.
Powdery mildews are important diseases of stone fruits and can cause significant crop losses in California. Species reported under current nomenclature include Podosphaera clandestina (peach, sweet cherry), P. leucotricha (peach), P. pannosa (almond, apricot, peach, plum), and P. tridactyla (almond, apricot, plum, occasionally sweet cherry). In a recent outbreak of powdery mildew on peach in the central valley of California, the sexual stage of P. pannosa was found for the first time on severely infected varieties in the winter of several years. Thus, the fungus survives as mycelium in stem lesions and as cleistothecia. Furthermore, based on the sexual stage, P. tridactyla was identified on peach for the first time in southern California. Anamorph identification of Podosphaera spp. using molecular assays is ongoing. In field studies on peach and sweet cherry, the disease was managed from causing crop losses using rotations of in-season applications of DMI, strobilurin, and quinoline fungicides starting at bloom and continuing to pit-hardening (peach) or to harvest (sweet cherry).
Characterization of Phytophthora citricola infecting almond, avocado, strawberry and walnut in California. R. G. BHAT (1) and G. T. Browne (1,2). (1) Dept. of Plant Pathology, UC Davis; (2) USDA-ARS, Davis, CA 95616.
Fifteen isolates of Phytophthora citricola from avocado, 46 from almond, three from strawberry, 18 from walnut and 11 from other hosts were characterized for genetic variation using amplified fragment length polymorphisms (AFLP) and for sensitivity to the fungicide mefenoxam. Also, 24 of these isolates were tested for pathogenicity on segments of almond shoots (cv. Drake). Cluster analysis using UPGMA indicated a high level of genetic diversity among the isolates (up to 58% Dice coefficient of dissimilarity) and five main clusters. Four of the clusters were dominated by isolates from individual hosts, two for almond and one each for avocado and walnut, while the fifth cluster had isolates from various hosts. Based on analysis of molecular variance of the AFLP data, 39.7% and 30.2% of the genetic variation was due to host and geographical location of isolates, respectively, while only 4.5% was due to isolate niche. About 83% of the isolates had growth reductions from 51 to 90% on V8 juice agar medium amended with mefenoxam at 1 ppm, and the growth of selected isolates remained constant at various concentrations of mefenoxam. Isolates (22 out of 24) from almond, avocado, strawberry and walnut were highly virulent on almond shoots. In California, populations of P. citricola exhibit genetic divergence associated with hosts and geographical locations.
Investigating associations between culturable soilborne fungi and replant disease of stone fruits in California. G. T. BROWNE (1), R. C. M. Lee (1), S. T. McLaughlin (1), J. H. Connell (2), S. M. Schneider (3), and R. Bulluck (1). (1) USDA-ARS, Dept. of Plant Pathology, Univ. of California, Davis 95616; (2) UCCE, Oroville, CA 95965; (3) USDA-ARS WMRL, Parlier, CA 93648.
In California, young almond and peach trees are subject to replant disease (RD) typified by poor growth rates and, in severe cases, mortality on land previously devoted to stone fruits. Specific RD causes are unknown, but it can occur in absence of plant-parasitic nematodes and is prevented by pre-plant soil fumigation. We are examining microbial roles in RD. Culture-based isolations were used to sample fungi from healthy and RD-affected trees in fumigated and non-fumigated plots, respectively. Root segments (<1 mm × 1 cm) were rinsed (R) in sdw or bleached for 2 min in 0.6% ClNaO then rinsed (B+R), blotted, and cultured on general and selective agar media. All isolates of fungi were transferred to 20% PDA and, when possible, identified to genus. Stepwise discriminant analysis was used to regress plant health status (healthy, RD-affected) on the incidences of fungal isolation. On Marianna 2624 rootstock of almond trees near Chico, CA incidences of Cylindrocarpon sp. on B+R roots and Fusarium spp. on R and B+R roots were RD predictors (P < 0.001). On Nemaguard peach near Parlier, CA, Rhizoctonia sp. and Pythium spp. on B+R roots and Fusarium spp. on R roots were predictors (P < 0.04). Isolates of disease-associated fungi caused root cortex necrosis on Nemaguard peach in greenhouse tests. Our results suggest a partial role of fungi in RD.
Effectiveness of stump removal in reducing Annosus root rot losses in Christmas tree plantations. G. A. CHASTAGNER and N. L. Dart. Washington State University, Puyallup, WA 98371.
Annosus root rot, caused by Heterobasidion annosum, is a significant problem in second and third rotation Pacific Northwest true fir Christmas tree plantations. In some Fraser fir plantations, more than 40% of trees are killed prior to harvest. In fields with high levels of disease it is recommended that growers remove stumps before replanting. Although this is a standard disease management practice in forest situations, its effectiveness in Christmas tree plantations with much shorter rotations is unknown. To determine the benefits of stump removal, mortality data were collected between 2001 and 2003 from three sites where growers had planted noble, Fraser, or grand fir seedlings next to stumps or after the stumps had been removed. During this 3-year period, mortality ranged from 7 to 13.9% when seedlings were planted next to stumps. Stump removal reduced mortality by 80.6 to 95.7%. If trees that died before 2001 are included in the benefit assessments, stump removal increased the number of healthy trees by an estimated 103 to 228 trees per acre.
Azoxystrobin: A new post-harvest decay control tool for citrus. A. COCHRAN (1), A. Tally (2), E. Tedford (3), and J. Adaskaveg (4). Syngenta Crop Protection, (1) Visalia, CA 93292; (2) Greensboro, NC 27419; (3) Roseville, CA; (4) University of California, Riverside, CA.
Azoxystrobin (2.08SC), a member of the strobilurin chemical class, applied solo or in combination with other postharvest fungicides on citrus fruit has demonstrated excellent post harvest control of green mold caused by Penicillium digitatum. In addition to green mold, azoxystrobin also provides good control of Diplodia natalensis and other common citrus decay fungi. Azoxystrobin will likely receive federal registration in 2005 and thus the unprecedented introduction of yet another new fungicide to the citrus industry. Azoxystrobin and Graduate, a new post harvest fungicide containing the active ingredient fludioxonil which has a different mode of action than azoxystrobin and received federal registration in 2004, applied to citrus fruit either alone or in combination offer an excellent alternative to either imazalil or thiabendazole, particularly where fungicide sensitivity is compromised due to fungicide resistance.
Predicting take-all in wheat crops using a quantitative DNA soil assay. M. G. CROMEY (1), S. Chng (1), S. Bithell (1), and A. McKay (2). (1) Crop & Food Research, Private Bag 4704, Christchurch, New Zealand; (2) SARDI, GPO Box 397, Adelaide 5001, South Australia.
The root disease take-all, caused by Gaeumannomyces graminis var. tritici (Ggt) is often severe where wheat crops are grown consecutively. It can also be severe in first wheat crops where wheat volunteers or certain grass weeds were common in previous break crops. A DNA soil test for Ggt was used to quantify pathogen levels in soils before wheat crops were sown. Take-all infection was assessed during grain fill. The DNA test was effective in predicting crops at low risk of take-all, although disease was sometimes more severe than expected when environmental conditions were particularly conducive to disease development. Paddocks with high levels of detected inoculum usually produced heavily infected crops, but this was not always the case. Soil sampling stage and method were shown to affect the measured levels of inoculum, and procedures have been developed to optimise detection. Data collected on environment, sites, soils, and crop management factors have been analysed to determine the factors that can influence the development of take-all for given levels of soil inoculum.
Xanthomonas campestris pv. carotae in seed carrot plants. F. CROWE and R. Simmons. Central Oregon Agricultural Research Center, Oregon State University, Madras, OR 97741.
Xanthomonas campestris pv. carotae (XCC) may grow abundantly on carrot foliage without causing symptoms of bacterial blight. To determine if the pathogen could be found within symptomless plants, filtrate from surface-sterilized, peeled, pureed roots sampled from commercial fields was dilution plated onto selective XCS medium. Stems and foliage were processed similarly. No XCC was recovered from inside seedlings sampled through the fall. XCC populations were detected in 10-15% of plants sampled pre- and post-flowering from mid-winter through summer. Populations of XCC increased through this period and ranged from 10(^4)-10(^10) colony forming units/g dry wt. From individual plants, XCC could be recovered from roots, foliage (including stems), or both. Symptoms were not observed on roots, stems or foliage. Similar results were found after carrot roots or foliage were inoculated, with or without wounding, prior to vernalization followed by isolations carried out after vernalization. The results indicate flowering carrot plants may tolerate high populations of XCC, externally and internally, without developing symptoms of bacterial blight.
Investigating possible roles of soilborne bacteria in replant disease of stone fruits in California. D. A. DOLL, G. T. Browne, D. A. Kluepfel, and R. C. M. Lee. USDA-ARS, Dept. of Plant Pathology, University of California, Davis, CA 95616.
Replant Disease (RD) often affects almond, peach, and other stone fruits in California when they are planted without precautions on land previously devoted to their production. RD symptoms include poor rates of tree growth and, in severe cases, tree mortality. Specific causes of RD are unknown, but it can occur in absence of plant parasitic nematodes and is prevented by pre-plant soil fumigation. We are examining associations between soilborne bacteria and RD. Culture- and DNA-based methods were used to sample bacterial populations from healthy and RD-affected trees in fumigated and non-fumigated plots near Chico and Parlier, CA. Culturable bacteria were isolated on 5% Tryptic Soy Agar by dilution plating from water suspensions of fine root segments (1 mm × 1 cm) and adhering soil, before and after surface sterilizing in 0.6% NaClO and grinding in water. Bacterial isolates were randomly selected and identified using 16s rDNA sequence analysis. In addition, 16s rDNA fragments were amplified from DNA extracted from soil. The rDNA fragments are being characterized by denaturing gradient gel electrophoresis and sequencing. Preliminary findings on bacterial associations with RD incidence will be reported.
Efficacy of fungicides against infections of garlic in Washington State. F. M. DUGAN, B. C. Hellier, and S. L. Lupien. USDA-ARS Western Regional Plant Introduction Station, Washington State University, Pullman, WA 99164-6402.
Fusarium proliferatum, F. oxysporum f. sp. cepae and Embellisia allii caused serious losses in 2001-2003 during garlic (Allium sativum) regeneration and storage for the National Plant Germplasm System in Pullman, Washington. When fludioxonil, thiophanate methyl or benomyl were used as pre-planting dips for cloves planted to the field, mean bulb weights in each treatment were higher than controls, but significantly so only for fludioxonil and thiophanate methyl. When these fungicides were used as pre-planting dips with soil artificially infested with the pathogens in a greenhouse, mean plant weights for fungicide treatments were again higher than controls, but results were significant only for benomyl. When benomyl and thiophanate methyl were used as post-harvest dips of bulbs from field soil, both were equally and significantly effective in reducing the mean fraction of cloves rotted per bulb. Deep-seated, artificial infections of cloves were not affected by fungicides even with dip times up to 180 minutes. Survival of the Fusarium spp. in field soil was confirmed by bioassay with a susceptible onion variety. Thiophanate methyl and fludioxonil have different modes of action, and may be as effective as benomyl as pre-planting and/or post-harvest dips for managing Fusarium and Embellisia diseases of garlic.
Wheat yield is suppressed by cereal cyst nematode (Heterodera avenae) in Union County, Oregon. S. A. EASLEY, R. W. Smiley, and J. A. Gourlie. Oregon State Univ., Columbia Basin Agric. Res. Center, Pendleton, OR 97801.
Most wheat in the Pacific Northwest is produced in low rainfall (below 16 in.) regions as a 2-yr rotation of winter wheat and summer fallow. Considerable wheat/fallow acreage is being converted to annual spring cereals produced without tillage. For irrigated and higher rainfall regions, wheat is usually rotated with other crops but is sometimes planted annually. Cereal cyst nematode (CCN) is widely distributed and does not cause economic damage to wheat rotated with summer fallow or non-hosts. CCN in Union County, OR was identified as Heterodera avenae using PCR/RFLP. Effects of H. avenae on wheat yields in Union County were investigated in 6 rainfed and irrigated experiments over 9 yr. Yields of annual spring and winter wheat were negatively correlated with initial densities of H. avenae eggs plus juveniles (from cysts). Aldicarb applied at planting improved spring wheat yield as much as 24 percent. Yield of annual winter wheat was as much as 50 percent lower than yield of winter wheat rotated with summer fallow or non-hosts. Wheat cultivars with genetic tolerance to H. avenae are needed for cereals produced annually.
Suppressive and inducive role of rhizosphere bacteria in sporangia production of Phytophthora cinnamomi. S. EHTESHAMUL-HAQUE*, V. Sultana*, E. Bent, E. Pond, B. McKee, J. Borneman, and J. A. Menge. Dept. Plant Pathology, Univ. of Calif., Riverside, CA 92521. *Visiting scholars, Karachi Univ., Pakistan.
Sporangia production by P. cinnamomi was examined in vitro using rhizospheric soils from healthy and diseased avocados, non-sterile soil extracts and bacteria isolated from these soils. Sporangia production was higher in mycelial mats buried in soil as well as in non-sterile rhizosphere soil extracts of diseased plants compared to healthy plants. Degradation of fungal mats buried in soil was not correlated with diseased or healthy plants. Two suppressive strains of Pseudomonas putida were isolated from the soil, however; one strain from healthy and one strain from diseased plants where mat degradation occurred at a high level. Several bacteria isolated from the rhizosphere of diseased avocados induced the production of large numbers of sporangia in autoclaved soil, soil extract and distilled water. Besides Pseudomonas, other species of bacteria were found to induce sporangia. These results suggest that the sporangial-inhibitory and sporangial-inducing bacteria in soil greatly influence the disease development.
Occurrence of Togninia fraxinopennsylvanica on esca-diseased grapevines (Vitis vinifera) and declining ash trees (Fraxinus latifolia) in California. A. ESKALEN, S. Rooney-Latham, and W. D. Gubler. Department of Plant Pathology, University of California, Davis, CA 95616.
Esca (black measles) and Petri disease (young esca) are two of the most destructive diseases of grapevines in California and other grape-producing countries. Both diseases are suspected of being caused by Phaeomoniella chlamydospora and multiple species of Phaeoacremonium. The teleomorph of Pm. aleophilum has been recently confirmed as Togninia minima (Tul. & C. Tul.) Berl. Reid. Teleomorphs of other Phaeoacremonium species have not yet been identified. In this study, perithecia of Pm. mortoniae were discovered on diseased grapevines (Vitis vinifera) in California. Perithecia were embedded in decayed vascular tissue of pruning wounds on cordons and trunks of grapevine (Cvs Johannisberg Riesling from Mendocino County, and Thompson Seedless from Madera County). Perithecia were also found in decayed vascular tissue of ash (Fraxinus latifolia) indicating that this species has a multiple host range. When plated onto PDA-tet media, ascospores formed colonies typical of Pm. mortoniae. Morphological and molecular data confirmed that the perithecia are in fact Togninia fraxinopennsylvanica (Hinds) Hausner et al. and that this fungus is the teleomorph of Pm. mortoniae. Perithecia of T. fraxinopennsylvanica were also produced in vitro by crossing compatible isolates of Pm. mortoniae.
Evaluation of fungicides for control of cavity spot in a disease nursery. J. J. FARRAR. Dept. Plant Science, California State University, Fresno, CA 93720.
Cavity spot of carrot is one of the most important diseases of fresh market carrots. Although the lesions are superficial, they decrease the cosmetic appeal of the carrot. In California, cavity spot is caused by Pythium violae, P. ultimum, P. sulcatum, and P. irregulare. Replicated experiments on cavity spot disease controls are often hampered by the lack of a field location with consistently high disease incidence. In order to effectively and efficiently evaluate control methods, a cavity spot disease nursery was developed at California State University, Fresno. The cavity spot disease nursery was established by growing three successive crops of susceptible carrots and inoculating with several isolates of P. violae, P. ultimum, and P. sulcatum. At the end of the third crop, a survey indicated a 3% disease incidence. During the fourth crop, the new fungicides Reason (fenamidone) and Ranman (cyazofamid) were compared with Ridomil Gold (mefanoxam) for disease control. Cavity spot incidence at harvest was not statistically different for the fungicides and all fungicides treatments had significantly reduced incidence compared to the untreated control.
Leveillula taurica in Washington state: A case history. D. A. GLAWE (1), F. M. Dugan (2), L. J. du Toit (3), Y. Liu (4), and J. D. Rogers (5). (1) Dept. of Plant Pathology, Washington State Univ., Puyallup, WA 98371; (2) USDA-ARS WRPIS, Washington State Univ., Pullman, WA 99164; (3) Dept. of Plant Pathology, Washington State Univ., Mt. Vernon, WA 98273; (4) Dept. of Biology, Univ. of Washington, Seattle, WA 98195; (5) Dept. of Plant Pathology, Washington State Univ., Pullman, WA 99164.
Leveillula taurica was unknown in WA until 2004. First found in central WA on onion (Allium cepa), powdery mildew of this host was observed there in 1996 but the fungus was not characterized. Subsequent investigation of potato (Solanum tuberosum) plants in a field adjacent to powdery mildew-infected onion plants determined that L. taurica coinfected potato along with Golovinomyces orontii, a potato pathogen known in WA for more than 50 years. Also in 2004, L. taurica was found on greenhouse-grown seaside arrow grass (Triglochin maritima) in Pullman, WA. Both teleomorph and anamorph occurred on this host and the ITS sequence was identical to those reported for L. taurica on other hosts in Australia and Iran. It appears that L. taurica was introduced and is now endemic.
Development and release of 'Shoshone' sainfoin (Onobrychus viciifolia) with tolerance to the northern root-knot nematode. F. A. GRAY, T. Shigaki, D. W. Koch, and R. H. Delaney. Dept. of Plant Sciences, University of Wyoming, Laramie, WY 82071.
The northern root-knot nematode, Meloidogyne hapla, is a devastating root parasite of sainfoin Onobrychus viciifolia. Varieties with resistance are currently not available. Sainfoin plants surviving for 16 months in the presence of M. hapla in southeast Wyoming were allowed to intercross to produce a seed line (WY-PX1-84). Surviving plants appeared healthy with dark green foliage compared to rogued plants which were severely galled and stunted. WY-PX-84 expressed tolerance to M. hapla in greenhouse tests with increased shoot and root biomass and lower plant mortality as compared to Remont sainfoin. Forage yields determined from 1996-2003 in Wyoming and Montana were slightly higher than Remont. Sainfoin can also be used for wildlife habitat restoration and as a legume component in the Conservation Reserve Program. WY-PX-94 has recently been released by the Agricultural Experiment Stations in Wyoming and Montana and the United States Department of Agriculture-Natural Resources Conservation Service as 'Shoshone.'
Detection of Podosphaera clandestina and Erysiphe necator in the air of cherry (Prunus avium L.) orchards and grape (Vitis vinifera L.) vineyards using PCR and species-specific primers. G. GROVE (1), J. Falacy (1), R. Spotts (2), D. Glawe (3), W. Mahafee (4), H. Galloway (1), and J. Lunden (1). (1) Washington State University Irrigated Agriculture Research and Extension Center, Prosser, WA; (2) Oregon State University Mid-Columbia Research and Extension Center, Hood River, OR; (3) Washington State University Puyallup Research and Extension Center; (4) USDA-ARS Horticultural Crops Research Unit, Corvallis, OR.
A sensitive, rapid, and accurate means to detect Podosphaera clandestina (Pc) and Erysiphe necator (En) in cherry orchards and grape vineyards (respectively) would be useful in disease management. The purpose of this study was to develop procedures for early detection of Pc or EC in orchard or vineyard air. PCR assays were developed to differentiate Pc or EC from other powdery mildews common in the northwest United States. DNA was extracted from mycelia, conidia, and/or cleistothecia collected from cherry leaves using a Burkard cyclonic surface sampler. Primer pairs were developed to select unique regions of the internal transcribed spacer (ITS) region of Pc or En ribosomal DNA. The respective primer pairs generated an amplicon from Pc or En, but did not generate amplicons from other erysiphaceous species collected from 46 disparate hosts. The assay facilitated detection of low levels Pc and En inoculum in respective orchard and vineyard air samples within hours of collection prior to disease onset. A method utilizing a Rotorod air sampler proved to be the most consistent for detection. The techniques detected propagules of Pc and En during ascospore releases induced by rain. Detection of both pathogens then ceased for a brief period and resumed immediately prior to the observance of mildew signs.
Control of grapevine powdery mildew: Timing of fungicide applications by use of the U C Davis Risk Assessment Model. W. D. GUBLER and C. S. Thomas. Department of Plant Pathology, University of California, Davis, CA 95616.
Powdery Mildew caused by Erysiphe necator is the most serious disease of grapevine. Control programs in the past used calendar based spray applications beginning from 40-52 cm of shoot growth. Timing for the first application was too late and caused applications to be eradicative rather than protective. Control programs often failed, fungicide resistance occurred, and products were lost. The U C Davis Risk Assessment Model was developed and validated statewide. This model was based on the effect of temperature on population increase and subsequent disease increase. The index fluctuates between 0-100. An indices of 60-100 indicates a reproductive rate of 5 days while an index of 0-30 indicates no reproduction. Use of the model allowed growers to stretch spray intervals during times of low to intermediate disease pressure and to shorten intervals when pressure was high. Over the past 8 years growers have saved 2-8 applications per year and have better disease control when using the model.
Population structure of Sclerotinia sclerotiorum in Washington State. I. JIMENEZ-HIDALGO (1) and N. J. Grunwald (2). (1) Washington State University and USDA-ARS, Prosser, WA; (2) Horticultural Crops Research Laboratory, USDA-ARS, Corvallis, OR.
In a previous study we showed that S. sclerotiorum isolates from pea in the Pacific Northwest, had higher genotypic diversity than the isolates from canola in Canada. The objective was to determine the population structure of S. sclerotiorum in eastern Washington State. 117 isolates were collected from 7 different fields of diverse crops (peas, beans, and coriander) and were genotyped using AFLPs and microsatellites. When considering the whole S. sclerotiorum population, 40 different fingerprints were identified with AFLPs and 18 clonal groups were observed. When using microsatellites, 85 genotypes were characterized, but 57.22% of the isolates had unique genotypes. If considering subpopulations separately, 24, 26 and 8 genotypes were identified in the pea, bean and coriander subpopulations respectively with AFLPs and 41, 47 and 9 different profiles with microsatellites, respectively. This data demonstrate that S. sclerotiorum in eastern Washington has a high genotypic diversity within and among populations corroborating previous observations.
New fungicide-sanitizer mixtures and recycling in-line drenches for postharvest decay control of citrus fruit. L. KANETIS (1), H. Förster (2), and J. E. Adaskaveg (1). Dept. of Plant Pathology, Univ. of California, (1) Riverside, CA 92521 and (2) Davis, CA 95616.
Green mold caused by Penicillium digitatum is the most important postharvest disease of citrus fruit. Over-usage of the older postharvest fungicides imazalil and TBZ has resulted in selection of fungicide resistance in the pathogen population. Three new fungicides (azoxystrobin, fludioxonil, and pyrimethanil), all belonging to different chemical classes, are being registered for postharvest use on citrus in the US. The new materials were found to be highly effective in controlling green mold. Fungicide mixtures and new recycling in-line drenches provided excellent control (>95%) and reduced the risk of resistance development. To prevent pathogen contamination of drench solutions, two oxidizing disinfestants were evaluated. Peroxyacetic acid was compatible and efficacious with all fungicides tested. Sodium hypochlorite was incompatible with azoxystrobin, imazalil, or pyrimethanil, but not with fludioxonil or TBZ. Thus, fungicide-sanitizer mixtures and in-line drenches were effective as decay control treatments and as anti-resistance strategies.
A pod necrosis disease ("chocolate pod") of snap bean (Phaseolus vulgaris) in Oregon caused by a strain of Clover yellow vein virus. R. C. LARSEN (1) and J. R. Myers (2). (1) USDA-ARS, Prosser, WA; (2) Oregon State University, Corvalis, OR.
Clover yellow vein virus (ClYVV) typically causes severe leaf mosaic symptoms and stunting in susceptible snap beans. During 2004, field-grown plants in the Willamette Valley, Oregon were observed with top necrosis and light brown discoloration on pods or "chocolate pod." Leaf and pod samples were collected and analyzed by ELISA using a potyvirus group-specific monoclonal antibody (MaB) (Agdia, Inc.) and a polyclonal antiserum to Bean yellow mosaic virus (BYMV). Total nucleic acid was also extracted and analyzed by RT-PCR using primers specific for BYMV and ClYVV. Positive results were obtained with the potyvirus MaB but not with antiserum to BYMV. Amplicons of the expected size were generated in RT-PCR reactions using primers specific only for ClYVV. The virus isolate characteristics were similar to a strain of ClYVV detected in the Great Lakes region in 2000-2004 transmitted by the soybean aphid (Aphis glycines), except that pod necrosis was more severe in that region and the virus was not detectable by ELISA using the potyvirus MaB.
The rise and fall of hop powdery mildew in the Pacific Northwest. W. F. MAHAFFEE (1), W. W. Turechek (2), C. S. Thomas (3), M. Nelson (4), C. M. Ocamb (5), and G. G. Grove (4). (1) USDA-ARS, Corvallis, OR 97330; (2) USDA-ARS, Beltsville, MD 20705; (3) Dept. Plant Path., Univ. California, Davis, CA 95616; (4) Dept. Plant Path., Washington State Univ., Prosser, WA 93350; (5) Dept. Botany & Plant Path., Oregon State Univ., Corvallis, OR 97331.
In 1996, hop powdery mildew was found in a greenhouse in the Yakima Valley of WA. By July 1998, it was found in all hop growing regions of ID, OR, and WA. Over the past six years, laboratory and field research has determined the impacts of diurnal temperature fluctuations, humidity, and host on disease development, spatial dynamics of disease spread, cultural practices that reduce disease development, and pathogen distribution. These efforts have culminated in an infection risk forecasting model and an integrated management system that is used on approximately 75% of US hop acreage. In 2002-2004, growers using the model to assist in fungicide applications reported 2.5 fewer applications and had 55% less incidence of cone infection per year. Combining the model with other cultural practices has helped reduce control costs from $980 to $230-490 per hectare depending on variety and grower risk aversion.
Soil flooding and solarization as potential management tools for Fusarium wilt of lettuce. M. E. MATHERON and M. Porchas. Yuma Agricultural Center, University of Arizona, Yuma, AZ 85364.
Fusarium wilt of lettuce, caused by Fusarium oxysporum f. sp. lactucae (Fol), was first detected in Arizona lettuce fields in 2001. Flooding and solarization of soil were evaluated as potential disease management tools. Containers (30 cm diameter × 25 cm deep) were buried in soil to serve as microplots. On July 13, containers were filled with soil naturally infested with Fol. Soil was then flooded or irrigated and covered with clear plastic for 15, 30, 45 or 60 days. Mean soil temperature for the duration of the trial at the 5 cm depth in nontreated, flooded and solarized soil was 40, 33 and 45°C. In the greenhouse, lettuce transplants were grown in soil collected from each microplot container at a depth of 2 to 7 cm. Plants grown in flooded or solarized soil for at least 45 days had no foliar or root symptoms of Fusarium wilt, whereas those grown in nontreated soil did display disease symptoms. When grown in nontreated, flooded and solarized soil, the mean fresh weight of lettuce plant tops was 80, 113 and 144 g, respectively, whereas root fresh weight was 8, 8 and 17 g, respectively. Further evaluation of these potential disease management tools is in progress.
Sweet corn crown and node necrosis is associated with reduced ear yields in the Willamette Valley of Oregon. N. L. MILLER and C. M. Ocamb. Dept of Bot & Pl Path., Oregon State Univ., Corvallis, OR 97330.
Sweet corn yields in the Willamette Valley of Oregon have been declining since the 1990’s. Severe root rot affects some plants, but has been absent in some fields where plants show secondary symptoms (low yield, leaf death). Necrosis in stalk nodes and crowns can be found in the absence of severe root rot in some affected fields. Studies were done to determine if there is a relationship between yield and necrotic crowns or stalk nodes. The relationship of node discoloration on fluid movement through the stalk was also examined. Longitudinal stalk sections of 100 plants were scanned from each of ten fields. An image analysis program was used to quantify the intensity of discoloration. Regression analysis indicated that plants with darker crown tissues have lower ear weights (r(^2) = 0.73). Plants with darker nodes allowed less fluid to pass through a 30-cm stalk section (r(^2) = 0.66). Lower yields may be due to decreased vascular conductance in symptomatic crown and stalk nodal tissues. Several Fusarium species are frequently isolated from symptomatic crown and stalk node tissues and pathogenicity studies are underway.
The Cereal Cyst Nematode is causing economic damage on rainfed wheat production systems of Turkey. J. M. NICOL (1), N. Bolat (2), E. Sahin (1), A. Tulek (2), A. F. Yildirim (2), A. Yorgancilar (2), A. Kaplan (2) and H. J. Braun (1). (1) International Maize and Wheat Improvement Center (CIMMYT), Ankara, Turkey; (2) Anadolu Agricultural Research Institute, Eskisehir, Turkey.
The Cereal Cyst Nematode Heterodera avenae is documented to cause economic yield loss worldwide in rainfed wheat production systems, however we have little knowledge with a closely related species H. filipjevi which has a widespread distribution in Turkey. Preliminary yield loss trials with 12 cereal varieties consisting of 7 replicated yield plots planted as a Split-Plot RCBD with pair wise varieties with and without the application of the Nematicide Temik (Aldicarb) were conducted in 0203 on two field locations in Turkey. The natural H. filipjevi initial and final population were measured the start and end of the season. Results clearly demonstrate the Cyst Nematode is economically important on rainfed winter wheat in Turkey, with average yield increase with Temik application of 27% Cifteler and 46% in Haymana. Further analysis of data showed strong significant regression equations between yield and initial density of H. filipjevi.
Field and laboratory based screening approach to identify resistance to dryland root rot complex in Turkey. J. M. NICOL (1), H. Hekimhan (2), A. Bagci (3), B. Tunali (2), E. Sahin (1), N. Bolat (2), A. F. Yildirim (2), A. Yorgancilar (2), H. J. Braun (1), R. Trethowan (1), and A. Hede (1). (1) CIMMYT International (International Wheat and Maize Improvement Center), PK 39 Emek, Ankara, 06511, Turkey; (2) MARA3 (Turkish Ministry of Agriculture and Rural Affairs), Turkey; (3) Selcuk University, Konya, Turkey.
Root, crown and foot root rots, including the complex of Crown Rot Fusarium (F. psuedogramiearum, F. culmorum) and Common Root Rot (Bipolaris sorokinana) are causing economic yield loss in many parts of the world where cereals predominate the cropping system and sub-optimal growing conditions and rainfed or limited irrigation practices are common. CIMMYT in collaboration with the Turkish Ministry of Agriculture have established an International field and laboratory screening program for identifying spring and winter wheat accessions with resistance to these root pathogens. This involves a 5 year field testing and greenhouse screening program. Furthermore, assessment of tolerance with the most promising lines is also occurring to identify accessions which combine resistance and tolerance to the dryland root rot complex. The strategy in place is described with reference to subsequent breeding and seed dissemination in addition to some of the most promising lines identified.
Two methods for distinguishing zoospores and cysts of Phytophthora ramorum. N. OCHIAI (1), L. D. Yarbrough (2), and J. L. Parke (2). Oregon State Univ., Corvallis, OR, (1) Dept. of Crop and Soil Sci.; (2) Dept. Bot. and Plant Path.
Plant pathogenic Pythium and Phytophthora spp. are often detected in recirculated irrigation water of nurseries and greenhouses. These oomycetes are likely present in water as zoospores or cysts. Lack of rapid, accurate methods to differentiate and quantify water-borne life stages limits our ability to study the survival and fate of these pathogens in recycled water systems. We are developing 2 methods which exploit differences in surface chemistry of zoospores and cysts to expedite visual enumeration or enable automated counting with flow cytometry. Calcofluor binds to cellulose of cyst walls but not to zoospore plasma membranes. Viewed with an epifluorescence microscope, cysts fluoresced bright blue while zoospores appeared dull green. Soybean agglutinin (SBA) binds to carbohydrates present on zoospore plasma membranes but absent from cyst walls. Upon laser excitation (488 nm), zoospores bound by SBA conjugated with Alexaflor488 fluoresced while cysts not bound by SBA did not. Preliminary results affirm the potential of flow cytometry to quantify mixed populations of zoospores and cysts.
Interaction between wheat and bacterial genotypes for rhizosphere colonization and root accumulation of Pseudomonas-derived 2,4-diacetylphloroglucinol. P. A. OKUBARA (1), B. B. Landa (2), and R. F. Bonsall (1). (1) USDA ARS, Root Disease & Biological Control Research Unit, Pullman, WA 99164-6430; (2) Departamento de Agronomía, Escuela Téchnica Superior de Ingenieros, Agrónomos y de Montes (ETSIAM), Universidad de Córdoba, Apartado 3048, Córdoba 14080, Spain.
Biocontrol isolates of Pseudomonas fluorescens that produce the antifungal metabolite 2,4-diacetylphloroglucinol (DAPG) can suppress soilborne pathogens, but the efficacy of the isolates depends partially on external factors. As part of a long-term research program to identify the genes and pathways in wheat that govern its interaction with biocontrol pseudomonads, we quantified steady-state levels of DAPG produced by two isolates of P. fluorescens on the roots of three Triticum aestivum L. (hexaploid wheat) cultivars four days after seed inoculation and growth in Petri plates. Both bacterial isolates aggressively colonized wheat roots, and produced DAPG. However, isolate Q8r1-96 produced more metabolite in culture and persisted in the wheat rhizosphere longer than Q2-87. As expected, accumulation of DAPG on roots of all three cultivars occurred at higher levels following colonization with Q8r1-96, compared to Q2-87. However, there was a striking differential in metabolite production by Q8r1-96 and Q2-87 on cv. Tara, whereas the differential on cv. Buchanan was much smaller. The accumulation patterns were not attributed to differences in rhizoplane population densities; both isolates reached an average of 2.0 × 10(^9) colony-forming units g(^-1) after four days, regardless of the cultivar. Previous studies have shown that steady-state levels of DAPG are correlated to the extent of root colonization in a host species-dependent manner. Our findings indicate that DAPG accumulation in the wheat rhizoplane is dependent on an interaction between cultivar and bacterial genotypes. Progress in identifying the determinants of differential accumulation will be presented.
Effect of salt and PEG induced water stress on rapid blight disease of turfgrass caused by Labyrinthula sp. M. W. OLSEN, M. J. Kohout, and D. M. Bigelow. Department of Plant Sciences, The University of Arizona, Tucson, AZ 85721.
Rapid blight is a disease of cool-season turfgrasses caused by Labyrinthula sp. In Arizona, disease is most problematic in turfgrass irrigated with poor quality water, and laboratory studies have shown that disease severity increases with increased salinity. However, the importance of stress induced by water deprivation alone in disease development has not been evaluated. Studies were done to compare symptom development and infection of turfgrass seedlings grown in solutions of equal osmolalities using salt or polyethylene glycol (PEG). Perennial rye seedlings were grown in hydroponic solution adjusted to EC 4.0 dS/m with NaCl or the equivalent osmolality of PEG6000. Plants were inoculated at the crown with 0.1 ml of a 10(^5) cell/ml suspension of Labyrinthula sp. All plants in the NaCl solution were infected and symptomatic after 7 days, while no plants in the PEG solution were infected or symptomatic. Non-inoculated control plants in both solutions were not infected or symptomatic. Results show that stress from water deprivation is not a factor in rapid blight disease development.
Recovery and detection of Phytophthora ramorum from sapwood of mature tanoak. J. L. PARKE (1,2), E. Oh (2), N. Ochiai (1), J. Stone (2), and E. Hansen (2). Oregon State University, Corvallis, OR 97331, (1) Dept. of Crop and Soil Science; (2) Dept. of Botany and Plant Pathology.
The sudden oak death pathogen Phytophthora ramorum causes lethal bole cankers on some members of the Fagaceae. Infection is believed to be restricted mainly to the inner bark and cambium. A portion of the bole from a naturally-infected mature tanoak was cut into 45 1-cm-thick transverse sections. Sections were photographed and tissue samples were removed from marked sites in the bark, cambium, and sapwood. Each sample was subdivided and plated onto a selective medium, processed for scanning electron microscopy (SEM), in situ PCR, and diagnostic PCR. In addition to recovery from bark, P. ramorum was isolated from discolored sapwood several cm away from the cambium, but not from adjacent healthy-appearing sapwood. Diagnostic PCR confirmed these findings. SEM revealed hyphae in xylem vessels of discolored wood, and in situ PCR confirmed their identity as P. ramorum. Imaging software was used to construct a 3-dimensional model of the bole, allowing visualization of the infection. These results indicate the potential for systemic spread of P. ramorum in tanoak.
Quantification of airborne hop powdery mildew inoculum, a molecular approach. A. B. PEETZ (1), W. F. Mahaffee (2), and G. G. Grove (3). (1) Dept. Botany & Plant Pathology, Oregon State Univ. Corvallis, 97330; (2) USDA-ARS Corvallis, OR; (3) Irrigated Ag. Research & Extension Center, Washington State Univ. Prosser, WA 99350.
Current disease forecasting models for Hop powdery mildew, Podosphaera macularis, assume inoculum presence. Evidence suggests that temperature fluctuations influence inoculum availability. Therefore, knowledge of inoculum presence and density and their relationship to environmental conditions may increase management efficacy by reducing pesticide use and cost of crop production. Primers designed to the internal transcribed spacer region of P. macularis ribosomal DNA have made inoculum detection possible using conventional and quantitative SYBR Green PCR methods. DNA extracted from conidia impinged on glass rods coated in silicon grease has been used as template for qPCR and we have successfully detected >100 spores. However, background SYBR green fluorescence unrelated to primer, template, or magnesium ion concentration is reducing sensitivity. Various fluorescent probes are being pursued as a means of increasing stringency and efficiency of the qPCR reaction.
Biocontrol of black foot disease of grapevines by using Glomus intraradices. E. PETIT and W. D. Gubler. Plant Pathology Dept., University of California, Davis, CA 95616.
Black foot disease, caused by Cylindrocarpon destructans and C. macrodidymum, is a recent but worsening problem in California vineyards. Symptomatic vines show necrotic lesions and vascular discoloration of roots while leaves show scorching resembling water stress. Eventually, the entire plant becomes stunted, and dies. Our objective was to test whether Glomus intraradices might be an effective biocontrol against this disease. Dormant Rupestris cuttings were rooted in the presence of G. intraradices and later inoculated with C. macrodidymum. Appropriate controls were also used. Eight months following inoculation with the pathogen, disease severity was rated. Root weights of plants inoculated with both mycorrhizae and the pathogen were significantly greater (P = 0.05) than root weights of plants inoculated with the pathogen alone. Furthermore, the number of root lesions caused by the pathogen was significantly reduced (P = 0.05) in plant inoculated with G. intraradices. Pre-inoculation of plants with G. intraradices significantly decreased the severity of black foot disease of grapevines.
Geocaching used for Eastern Filbert Blight education. J. W. PSCHEIDT. Dept. of Bot. & Pl. Path., Oregon State Univ., Corvallis, OR 97330.
Eastern Filbert Blight (EFB), Anisogramma anomola, occurs on hazelnut trees in riparian, residential and orchard areas in western Oregon. Extension has used traditional media vehicles to educate the public on EFB symptoms. Geocaching is a sport where a container (the cache) is hidden, its geographical coordinates are posted on the web and the goal for others is to try to find it using GPS devices. Two caches were established to educate geocachers on symptoms of EFB. The "Hazel Hut" consisted of a plastic shelter with a bulletin board set in a hazelnut orchard near Corvallis, OR. The "EFB Puzzle", a complicated multi-cache, started at the same location but involved finding puzzle pieces hidden in other orchards or riparian areas. Five other caches (non-EFB or disease related) were placed at Extension offices to asses the frequency of visits in similar geographic locations. After one year, the non-EFB caches averaged 65 visits while the EFB informational cache received 59 visits, 26 of which went on to complete the EFB puzzle tour in an averaged of 53 days, ranging from 4.5 hrs to 283 days. This work demonstrated that it is possible to educate the general geocaching public on symptoms of a plant disease.
Role of Fusarium species in rusty root development on ginseng roots. Z. K. PUNJA, A. Wan, and M. Rahman. Department of Biological Sciences, Simon Fraser University, Burnaby, BC V5A 1S6, Canada.
Rusty root of ginseng causes reddish-brown spots and discoloured areas on roots, usually at the crown, which become dark brown, raised and corky over time. The cause(s) of rusty root are presently unknown. Affected roots collected during 2003 and 2004 were plated onto different culture media to recover microbes. Fusarium was most frequently isolated, with F. solani, F. equiseti, F. culmorum, F. avenaceum and F. sporotrichioides recovered in order of decreasing frequency. All species except F. solani were also recovered from barley and wheat straw mulch from ginseng gardens. In vitro pathogenicity tests and greenhouse inoculations of ginseng roots revealed that F. equiseti induced reddish-brown lesions resembling rusty root symptoms. Other lesser pathogenic species were F. culmorum, F. avenaceum, and F. sporotrichioides, while F. solani and F. graminearum were non-pathogenic. Histopathological studies of rusty root tissues revealed mycelium in the upper 8-10 cell layers of the root. Phenolic compounds, peroxidase, polyphenoloxidase, and phenylalanine ammonia lyase were significantly higher in the affected tissues. Rusty root of ginseng is a host defense response following infection by Fusarium species, notably F. equiseti, in an attempt to restrict pathogen colonization.
Development of rapid diagnostic tools to identify viruliferous and non-viruliferous stubby root nematodes in the Pacific Northwest. E. RIGA (1), R. Larsen (2), R. Neilson (3), and N. Guerra (1). (1) IAREC, Washington State University, Prosser, WA, 99350; (2) USDA-ARS, Prosser, WA, 99350; (3) Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA, Scotland.
Stubby root nematodes are becoming of increasing importance to the potato industry in the Pacific Northwest as they are vectors of Tobacco Rattle Virus (TRV), the causal agent of Corky Ringspot disease. Paratrichodorus allius is one of the main stubby root nematode species in Washington State. The current method for determining if P. allius are viruliferous for TRV takes several weeks. Therefore, a rapid molecular assay has been developed using RT-PCR to identify viruliferous nematodes. The technique can detect TRV in as few as five nematodes. In addition to the presence of P. allius a second morphologically similar, stubby root nematode, Paratrichodorus teres has been identified using molecular fingerprinting techniques.
Real-time PCR for quantification of decay spore populations in packinghouse water. M. SERDANI and R. A. Spotts. Mid-Columbia Agricultural Research and Extension Center, Oregon State University, Hood River, OR 97031.
Pear packinghouses need a rapid, accurate method to determine concentration of decay spores in dump tank and flume water in order to know whether the level is above or below the threshold for serious decay problems. Traditional plate counts may take several days and are easily overgrown by opportunistic fungi and yeasts. Real-time PCR was explored as a faster and more accurate method to quantify DNA from packinghouse water. Water samples were taken from packinghouses in Oregon and Washington, and DNA extracted and quantified using real-time PCR. Results were used to determine fungal spore populations of Penicillium expansum and Mucor piriformis in the water. Several challenges were encountered, including possible detection of dead spores, interference of orchard and packinghouse chemicals with qPCR, and variation in sensitivity of different extraction kits and protocols. Once all these questions are answered, we will be able to determine the concentration of decay spores in dump tank and flume water so decay control decisions can be made based on previously established spore threshold values.
Resistance to root-lesion nematode (Pratylenchus thornei) in wild relatives of wheat. J. G. SHEEDY (1,2), J. P. Thompson (2), and J. Irwin (3). (1) Columbia Basin Ag. Res. Center, Oregon State Uni., Pendleton, OR 97801; (2) Leslie Research Centre, Queensland Dept. Primary Industries and Fisheries, Toowoomba, Australia 4350; (3) CRC Tropical Plant Protection, Uni. of Queensland, St. Lucia 4072.
Wheat (Triticum aestivum, BBA(^u)A(^u)DD) is a hexaploid comprised of three genetically related genomes. Pratylenchus thornei is a migratory root-endoparasitic nematode that feeds in the cortex of wheat and can reduce yield by 70% in intolerant cultivars. The existence of a large reservoir of useful genes in the wild relatives of wheat is apparent from the adaptation of the various wild forms to different environments. A total of 148 wild wheat accessions (WWA) including Aegilops speltoides (SS; B/G), T. urartu (A(^u)A(^u)), T. monococcum (A(^m)A(^m)), T. timopheevii (GGA(^u)A(^u)) and T. turgidium (BBA(^u)A(^u)) and 274 Iranian landrace wheats (ILW) were tested for resistance to P. thornei. Twenty-six WWA (8 Ae. speltoides; 9 T. urartu; 8 T. monococcum; 1 T. turgidum ssp. dicoccoides) and four ILW proved to be more resistant than the current best source of resistance, GS50a. P. thornei resistance genes exist on all three genomes of wheat and can now be pyramided to produce higher levels of resistance.
Pathogenic variation among isolates of fungi associated with crown rot of wheat. R. W. SMILEY, S. A. Easley, and J. A. Gourlie. Oregon State Univ., Columbia Basin Agric. Res. Center, Pendleton, OR 97801.
Fusarium culmorum (Fc), F. pseudograminearum (Fp), Bipolaris sorokiniana (Bs), and other species are associated with crown rot of wheat in the Pacific Northwest (PNW). Multiple isolates of Fc, Fp and Bs were compared for pathogenicity to a single spring wheat cultivar in a field experiment performed over two years and two locations. Data composited to include all isolates for individual species indicated that each species reduced stand establishment and tillering, and increased the incidence and severity of crown rot. Yield was significantly reduced by Fc and Fp but not by Bs. For each species, pathogenicity of isolates varied between locations and years, indicating an isolate × environment interaction. Variable responses to seasonal environments, for isolates within species, may explain the annual variation in species considered most dominant in causing crown rot within individual fields and regions. Mixtures of multiple isolates for each species are required for inoculated field experiments, and genetic tolerance and/or resistance to F. culmorum and F. pseudograminearum are required for wheat cultivars in the PNW.
Annual spring wheat yields are suppressed by root-lesion nematodes in Oregon. R. W. SMILEY, S. A. Easley, and J. A. Gourlie. Oregon State Univ., Columbia Basin Agric. Res. Ctr., Pendleton, OR 97801.
Soils in rainfed wheat fields planted annually in the Pacific Northwest are often infested by high populations of the root-lesion nematodes Pratylenchus thornei, P. neglectus, or both. Spring wheat cultivars varying in tolerance and resistance to these species were planted with and without aldicarb in 27 replicated split-plot experiments over 5 years in eastern Oregon. Effects of nematode density on growth and yield of direct-seeded (no-till) annual spring wheat were examined. Aldicarb reduced density of Pratylenchus spp. in roots and reduced foliar canopy temperature as much as 4°C. In P. thornei-infested soil, aldicarb improved yield by 113 percent for Machete (an intolerant/susceptible cultivar; I/S) and 67 percent for Krichauff (tolerant/moderately susceptible). Aldicarb did not improve yield in soil with a low population of Pratylenchus. Yield suppression by P. neglectus was 8 to 36 percent for Machete and Spear (I/S), except where it reached 71 percent in soil also infested with other root pathogens. Wheat cultivars with tolerance and resistance to both P. thornei and P. neglectus are needed for annually cropped fields.
Potential use of glyphosate herbicide in integrated control of Meruliporia incrassata. M. F. STONER. Dept. Biological Sciences, California State Polytechnic University, Pomona, CA 91768.
Meruliporia incrassata (MI) causes devastating decay in wood structures. Peculiar abilities of MI include migration through soil and root systems or over non-wood materials by rhizomorphs and mycelium; translocation of water via rhizomorphs to decay sites; and multiple survival strategies outside structures. Tests at decay sites showed that spraying of active mycelium and basidiophores, and injections of rhizomorphs with liquid formulations of glyphosate (2% active ingredient with foam, Monsanto) killed or weakened MI structures. Necrotic symptoms appeared 2-3 days after treatment. Tissue analyses and observations indicated that glyphosate was bi-directionally translocated. Necrosis in rhizomorphs, as observable, extended at least 5 feet from treatment points. Results point to a novel way to kill or weaken MI where it resides threateningly under concrete slab-on-grade foundations or in other inaccessible places. At a residence invaded by rhizomorphs from sub-slab sources, glyphosate spraying and injections 4.5 years ago, together with non-chemical abatement practices, have so far prevented reinvasion.
Culturable populations of Erwinia amylovora do not persist on mature symptomless winter pear fruit. T. N. TEMPLE, V. O. Stockwell, and K. B. Johnson. Dept. of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331.
Erwinia amylovora colonizes pear flowers, but less is known of its potential to colonize healthy fruit. We inoculated immature pear fruit in orchards with E. amylovora strain Ea153N as resuspended lyophilized cells or as ooze from tissue infected by Ea153N. Populations of lyophilized Ea153N decreased to nondetectable levels after 14 days; cells in ooze also showed poor survival but persisted on fruit longer than freeze dried cells. We tested the ability of Ea153N to migrate into symptomless pear fruit from diseased branches. Internal core tissues of mature fruit were assayed with an enrichment technique and nested PCR; the pathogen was not detected in fruit from diseased trees. In postharvest experiments, Ea153N inoculated into small wounds on fruit did not survive a cold storage period. In surveys of 32 commercial orchards, some with fire blight, E. amylovora was not detected on fruit (N = 3200) sampled at harvest. Our data indicate that E. amylovora is a poor epiphyte on pear fruit, and that mature symptomless winter pear fruits subjected to a cold conditioning period are unlikely to harbor this pathogen.
Botryosphaeria species associated with wedge shape canker on Vitis vinifera in California. J. R. URBEZ TORRES (1), G. M. Leavitt (2), T. M. Voegel (1), and W. D. Gubler (1). (1) Dept. Plant Pathology, University of California, Davis, CA 95616; (2) U. C. Cooperative Extension, 328 Madera Ave. Madera, CA 95616.
Wedge-shaped cankers in grapevines had been thought to be associated mainly with Eutypa dieback throughout California and occasionally with B. rhodina or "Bot canker disease" in the southern part of the state. In order to determine the occurrence of Botryosphaeria species in California, a field survey was carried out throughout the major grape producing counties. Typical wedge shape vascular cankers were collected from grapevine spurs, cordons and trunks. Morphological identification along with phylogenetic analysis of the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rDNA and a partial sequence of the beta-tubulin gene showed that at least five other Botryosphaeria species, B. obtusa, B. stevensii, B. australis, B. parva and B. dothidea occur in grapevines in California. Botryosphaeria species were found in all grapevine production areas surveyed and the high percentage of cankers yielding Botryosphaeria throughout the state has highlighted the importance of these fungi in California grapevine decline.