Posted online January 29, 2001
Comparison of Microsphaeropsis spp. isolates. J. BERNIER (1), C. A. Levesque (2), and O. Carisse (1). Agriculture and Agri-Food Canada; (1) 430 Gouin Blvd., St-Jean-sur-Richelieu, Qc, Canada, J3B 3E6; (2) 960 Carling, Ottawa, On, Canada, K1A 0C6. Publication no. P-2001-0001-NEA.
Two fungal isolates (P130A and P176A) recovered from apple leaf litter and recognized as potential biocontrol agents were identified as Microsphaeropsis arundinis by the International Mycological Institute. Because these two isolates displayed major morphological differences, two additional isolates (M. arundinis IMI 294735 and Microsphaeropsis sp. DAOM 198536) were acquired for comparison. Morphological characters and physiological tests revealed two pairs of strains with high degree of similarity: isolates P130A and DAOM 198536, and isolates P176A and IMI294735. Likewise, as revealed by thin-layer chromatography, production of secondary metabolites by P130A and DAOM 198536 was similar but different from P176A and IMI 294735. Furthermore, RFLP analyses revealed that isolates P130A and DAOM 198536 were genetically closely related to each other and differed from isolates P176A and IMI 294735. Based on the degree of divergence revealed by these tests, we concluded that the four isolates represented two distinct species.
Blue mold decay of apples reduced by post-harvest treatment with harpin. G. de CAPDEVILLE (1), S. V. Beer (1), C. L. Wilson (2), and J. R. Aist (1). (1) Dept. Plant Pathology, Cornell University, Ithaca, NY 14853; (2) USDA-ARS, Appalachian Fruit Research Station, Kearneysville, WV 25430. Publication no. P-2001-0002-NEA.
Harpin, a protein produced by Erwinia amilovora and involved in its pathogenesis of apple, induces disease resistance in tobacco and other plants. We explored the ability of Messenger™, the commercial formulation of harpin, to induce resistance in harvested apple fruits to blue mold caused by Penicillium expansum. Red Delicious fruits were harvested and sprayed with Messenger™ at 0, 40, 80, and 160 micrograms of harpin/ml. At 48, 96, and 144 hours after treatment, fruits were wound-inoculated with spore suspensions of P. expansum at 10(^3), 5 × 10(^3), or 10(^4) spores/ml. The diameters of the resulting lesions were directly proportional to inoculum concentration. Significantly fewer fruits treated with Messenger™ became infected than the controls, and disease progress was considerably reduced. Fruits inoculated 96 h after treatment with 80 micrograms/ml harpin had the least disease. Disease control was greater in tests with lower concentrations of inoculum. Harpin appears promising as a biocontrol agent for reducing blue mold decay of apples.
Molecular identification of the biocontrol agent Pseudozyma flocculosa leading to a quality control test. S. J. CARON (1), T. J. Avis (1), R. C. Hamelin (2), and R. R. Bélanger (1). (1) Université Laval, Québec, Q Canada; (2) Ressources Naturelles Canada, Québec, Canada. Publication no. P-2001-0003-NEA.
Pseudozyma flocculosa, a biocontrol agent of powdery mildew fungi, has completed numerous steps towards its commercialization as a biofungicide. In this process, identity and genetic stability of the antagonist must be ascertained to ensure integrity of the product and to protect intellectual property. Authentication of isolates is critical for consistent results in commercial trials as well as in the process of mass production. Ribosomal DNA distinguished P. flocculosa from other Pseudozyma species and identified two previously unknown isolates as P. flocculosa. Moreover, randomly amplified microsatellites revealed three distinct P. flocculosa strains among the tested isolates. These results permitted the development of a quality control test of the biocontrol agent. Multiplex PCR built with the ribosomal DNA primers enabled the identification of P. flocculosa from other related species and contaminants. This multiplex PCR test may also be adapted to include other markers such as genes involved in biocontrol properties of P. flocculosa.
Physical mode of action of monopotassium phosphate against Uncinula necator infections on grape leaves. J. E. CARROLL and W. F. Wilcox. Dept of Plant Pathology, Cornell University, NYSAES, Geneva, NY 14456. Publication no. P-2001-0004-NEA.
Experiments were conducted to determine if monopotassium phosphate (MKP; trade names = eKsPunge, Nutrol) has protectant or eradicant activity against Uncinula necator (grapevine powdery mildew). Leaves of 'Chardonnay' grape cuttings were sprayed with either a 1% solution of MKP or water, plus 500 ppm Tween20, at various times before or after inoculation with conidia of U. necator. After the start of each experiment, test plants were maintained in specially designed exclusion chambers to thwart cross-contamination from extraneous sources. Plants were rated for disease severity and incidence at 14 days post-inoculation in the protectant study and at 7 days post-treatment in the eradicant study. Discs were removed from leaves in the eradicant study to quantify pathogen sporulation. MKP had no protectant activity against U. necator. Eradicant activity was significant and was greatest when MKP was applied 3 days after inoculation, providing 99% and 76% control of disease severity in the two trials. Sporulation was reduced 50 to 95% when MKP was applied 3 to 10 days after inoculation.
Impact of upright dieback in one cranberry bed in Massachusetts. N. J. CATLIN and F. L. Caruso. University of Massachusetts, Cranberry Experiment Station, East Wareham, MA 02538. Publication no. P-2001-0005-NEA.
Upright dieback disease is a persistent problem in cranberry beds in all areas where cranberries are cultivated. Although it is seldom devastating, an estimated 20-25 percent of uprights can show symptoms in severe cases. However, little is known about the effects of this disease on yield or long-term vine health. Healthy and diseased areas of a cranberry bed cv. Early Black were monitored during the course of the growing season in order to assess the impact of the disease. Density of healthy and diseased uprights, density of vegetative and flowering uprights, fruit set, and berry yield were determined. In general, decreased yield was associated with higher incidence of upright dieback. Further relationships between these factors will be discussed, as well as preliminary observations as to the causal agent(s) of the disease.
Changes in protein profile of postharvest tomato in response to UV-C and Botrytis cinerea infection: pathogenesis-related proteins. M. T. CHARLES (1,3), A. Asselin (2), J. Grenier (2), and J. Arul (1,3). (1) Horticultural Research Center; (2) Dept. of Plant Science; (3) Dept. of Food Science and Nutrition, Laval University, Quebec, PQ Canada, G1K 7P4. Publication no. P-2001-0006-NEA.
Changes occurring in protein content and profile of tomato treated with hormic UV-C were studied. In UV-treated fruit, an increase in protein content after treatment was observed. Rate of protein degradation was slower in UV-treated fruit. PAGE showed that UV affected the protein profile of tomato by: preventing or delaying the expression of some proteins probably related to fruit ripening; enhancing the expression of several constitutive proteins of which, an acidic beta-1,3-glucanase, three acidic chitinases, and three basic chitinases; and inducing the synthesis of six new proteins. Among the UV-C induced proteins, three (a basic beta-1,3-glucanase and two acidic chitinases) were likely true pathogenesis-related (PR) since they were also induced in response to inoculation of control fruit with Botrytis cinerea. It is likely that the PR proteins with glucanohydrolase activities induced by UV are an integral part of the resistance observed in UV-treated tomato.
Genetic transformation of Pseudozyma flocculosa, a biocontrol agent of powdery mildews. Y. L. CHENG (1), F. Belzile (1), P. Tanguay (2), L. Bernier (2), and R. R. Bélanger (1). Université Laval, Québec, Qc, G1K 7P4, Canada. (1) Département de Phytologie; (2) Centre de Recherche en Biologie Forestière. Publication no. P-2001-0007-NEA.
We report here the development of a PEG-mediated transformation method for Pseudozyma flocculosa, a fungus antagonistic to powdery mildew fungi. Several heterologous vectors which harbored various selectable markers under the control of different promoters were tested. Molecular analyses demonstrated that transformation was successful using a plasmid pSce1-Hyg conferring Hygromycin B resistance under the control of the Ustilago maydis hsp70 promoter and terminator sequences. One to forty transformants were routinely obtained per 10 micrograms linearized DNA per 10(^8) protoplasts. CHEF electrophoresis separated the genome of P. flocculosa into at least 11 chromosomes with sizes ranging from 0.55 Mb to 2.9 Mb. Hybridization with the plasmid showed that the transformants of P. flocculosa harbored multiple tandem copies of the introduced vector at each integration site and, depending on the transformant, the integration events occurred randomly in one to several chromosomes.
Control of downy mildews on miniature rose and snapdragon. M. DAUGHTREY and M. Tobiasz. LIHREC, Dept. of Plant Pathology, Cornell University, Riverhead, NY 11901. Publication no. P-2001-0008-NEA.
Two concurrent greenhouse experiments were conducted to evaluate new fungicides for downy mildew control on rose cultivars 'Canyon Cupido' and 'Favorite Cupido' and snapdragon 'Rocket Mix'. Treatments (oz/100 gal; interval) were: trifloxystrobin (Compass 50WG 1.0; 7d and 2.0; 14d), trifloxystrobin + fludioxonil (Compass 1.0 + Medallion 50W 1.0; 14d), azoxystrobin (Heritage 50WP 2.0; 14d), dimethomorph + mancozeb (Stature MZ 69WP 28.0; 7d) and copper hydroxide + mancozeb (Junction 61.1DF 56.0; 7d). Sprays were applied from 21 Mar to 19 Apr 2000. There were 5 replications of 3 plants of each cultivar in randomized complete blocks on plastic-tented greenhouse benches supplied with humidifiers. After the first spray, sporangia collected from infected commercial crops were sprayed onto their respective hosts. Symptoms occurred on all untreated plants. On roses, defoliation was best reduced by Stature MZ. All but the Heritage and the 1.0 oz; 7d Compass treatment reduced leaflet symptom incidence in 'Favorite Cupido'. On snapdragons, all treatments reduced disease incidence. Snapdragons treated with Heritage or Stature MZ did not develop symptoms.
Characterization of Colletotrichum gloeosporioides isolates from ornamental lupines in Connecticut. W. H. ELMER (1), H. A. Yang (2), and M. W. Sweetingham (2). (1) CT Agr. Expt. Sta., New Haven, CT 06504 USA; (2) Coop. Res. Centre for Legumes in Mediterranean Agric., Univ. of Western Australia, Nedlands WA 6907, AUSTRALIA. Publication no. P-2001-0009-NEA.
Twenty-six isolates of Colletotrichum gloeosporioides were isolated from diseased ornamental lupines (Lupinus spp. 'Russell Hybrids') in seven different nurseries in CT from 1996 to 1998. Three isolates from New Hampshire, New York, and Utah were also included. All isolates were pathogenic on lupine and vegetatively compatible with each other. Representative isolates were compared to lupine isolates from Quebec and France (COL-1 group), and from Australia and France (COL-2 group). Both groups cause anthracnose of ornamental and forage lupines in these countries. The CT isolates were vegetatively compatible with the isolates in the COL-2 group and had DNA fingerprint profiles consistent with isolates in the COL-2 group. Isolates in the COL-1 group were vegetatively compatible only with each other and had RAPD profiles that differed from the COL-2 group. These assays provided persuasive evidence that the isolates from CT represent a clonal population and belong to COL-2 group.
Comparison and contrast of ontogenic resistance to Uncinula necator in Chardonnay and Concord grape berries. A. Ficke, D. M. GADOURY, R. C. Seem, M. Goffinet (1), and I. B. Dry (2). (1) NY State Agric. Exp. Stn., Geneva, NY 14456; and (2) CSIRO, Adelaide, SA, Australia. Publication no. P-2001-0010-NEA.
Fruit of Vitis labruscana 'Concord' (CO) and V. vinifera 'Chardonnay' (CH) differ in resistance to powdery mildew. When CO and CH berries were inoculated at several growth stages, CH developed more severe disease, and remained highly susceptible for 7-10 days longer than CO. In both cultivars, ontogenic resistance reduced formation of secondary hyphae, and colony growth and viability; but to a greater degree, and at an earlier growth stage, in CO. Similarly, ontogenic resistance increased the latent period from 6 da to 10 da in CO, but only from 6 da to 8 da in CH. Penetrated epidermal cells of both cultivars accumulated phenolics within 24 hr, resulting in cell discoloration. Diffuse infections developed when berries were inoculated just as ontogenic resistance was strongly expressed, and predisposed CH, but not CO berries to Botrytis cinerea. In both CO and CH fruit, ontogenic resistance appears to operate similarly, and at multiple levels, but the timing and magnitude of its expression results in substantial differences in apparent susceptibility.
Induction of chalcone synthase and chalcone isomerase following elicitation of cucumber plants infected with powdery mildew. B. FOFANA (1), C. Labbé (1), A. Séguin (2), and R. R. Bélanger (1). (1) CRH, Univ. Laval, G1K 7P4 Quebec, Canada; (2) CFL, 1055 rue PEPS, G1V 4C7 Quebec, Canada. Publication no. P-2001-0011-NEA.
Cucumber plants are reported to produce fungitoxic metabolites in response to infection by powdery mildew and an eliciting treatment. These defense secondary metabolites named phytoalexins (PA) are mainly flavonoids and isoflanoids. We report here the biochemical and molecular aspects of induced resistance in infected plants elicited weekly. The role of chalcone synthase (CHS), chalcone isomerase (CHI) and isoflavone reductase (IFR) was studied in relation with PA biosynthesis for their activity and transcriptional levels. Our results showed that CHI activity was higher in elicited plants compared to water-treated plants and was optimal 48 h after the first treatment. On the other hand, the activity reached a maximum as early as 4 h after the fourth treatment, suggesting a cumulative effect of the elicitor. With CHS, activity was three times higher in elicited plants 48 h after the fourth treatment compared to controls. Based on these results, CHI and CHS appear to be expressed coordinately in elicited plants whereas IFR was not induced in cucumber.
Bacterial leafspot of fenugreek: A new disease in New Jersey caused by Pseudomonas syringae pv. syringae. M. L. FOGG (1), D. Y. Kobayashi (1), S. A. Johnston (1), and W. L. Kline (2). (1) Dept. Plant Pathology, Rutgers Univ., New Brunswick, NJ 08901; (2) Rutgers Cooperative Extension, Millville, NJ 08332. Publication no. P-2001-0012-NEA.
Leaf spot on fenugreek (Trigonella foenum-graecum) was observed in a New Jersey commercial field during the summer of 2000. Initial symptoms included angular, water-soaked areas visible on both the abaxial and adaxial leaf surfaces, which progressed to necrotic lesions with chlorotic halos. In severe cases, lesions progressed throughout entire leaves and eventually led to defoliation. A bacterium isolated from diseased tissue fluoresced on King's B agar, tested negative for oxidase and arginine dihydrolase activities, and elicited the hypersensitive reaction on tobacco and pepper. The bacterium was identified as Pseudomonas syringae pv. syringae using Biolog and fatty acid analysis. Inoculation of cell suspensions into leaves of young fenugreek plants resulted in the appearance of disease symptoms similar to those observed in the field. This is believed to be the first report of a bacterial leaf spot on fenugreek in the United States.
Optimizing management of peach rusty spot epidemics. L. A. Furman, N. LALANCETTE, and J. F. White. Dept. of Plant Pathology, Rutgers University, New Brunswick, NJ 08901. Publication no. P-2001-0013-NEA.
Peach rusty spot, thought to be induced by the apple powdery mildew fungus Podosphaera leucotricha, has caused significant yield loss in NJ orchards. Currently, fungicide applications during early fruit growth are considered important for control, but exact timing and number of sprays are not known. This experiment was aimed at optimizing disease management by determining minimum number of sprays needed to achieve maximum reduction in the infection rate (r) and carrying capacity (K) of the epidemic. Beginning at petal fall, different numbers of myclobutanil sprays were applied as treatments to Jerseyqueen trees in a randomized complete block design. Nonlinear regression analysis was used to fit either the monomolecular or logistic model to disease progress data, allowing estimation of r and K. The r parameter decreased in a negative exponential fashion as number of fungicide applications increased; a modified negative exponential, Newton's law of cooling, was then found to better describe the data. K approached its minimum at approximately 4 sprays, and areas under disease progress curves indicated 3-4 sprays were necessary for optimum disease control.
Temporal analysis of peach rusty spot epidemics. L. A. FURMAN, N. Lalancette, and J. F. White. Dept. of Plant Pathology, Rutgers University, New Brunswick, NJ 08901. Publication no. P-2001-0014-NEA.
Rusty spot epidemics, thought to be caused by Podosphaera leucotricha, were studied in Jerseyqueen (JQ, 1999-2000) and Jerseyglo (JG, 2000) orchards. Disease incidence and severity were calculated from successive disease assessments on fruit from 4-5 replicate trees per orchard. Disease progress curves indicated epidemics could be divided into growth, static, and decline temporal phases. Nonlinear regression analysis of the growth phase indicated the monomolecular model was most appropriate for JQ99; however, insufficient number of assessments prevented detection of an exponential increase. The logistic model gave the best fit for describing disease progression for JQ00 and JG00. Similar carrying capacities (K) of 0.85 were observed on JQ in each year, while a lower K of 0.39 was estimated for JG00. Weighted absolute infection rates were 0.062, 0.042, and 0.025 for JQ99-00 and JG00 epidemics, respectively. On JQ99-00, linear regression analysis of the static phase revealed no significant change in disease over time, while significant disease reduction was observed during the decline phase. These results suggest rusty spot epidemics may be polycyclic.
Genome organization and sequence analysis of Blueberry red ringspot virus, a member of the family Caulimoviridae. B. M. GLASHEEN, J. J. Polashock, D. M. Lawrence, and B. I. Hillman. Department of Plant Pathology, Rutgers University, New Brunswick, NJ 08901-8520. Publication no. P-2001-0015-NEA.
Blueberry red ringspot virus (BRRV) is a member of the family Caulimoviridae that causes economically important diseases of blueberry and cranberry. Using traditional cloning and inverse PCR, we have synthesized and sequenced clones that represent the complete 8300 bp double-stranded DNA genome of BRRV. The most conserved regions of the BRRV genome relative to other caulimoviruses are the putative coat protein and reverse transcriptase genes. A 6X histidine-tagged recombinant protein derived from sequences representing 60% of the putative coat protein gene was purified and used to raise an antibody that is immunoreactive against virus particle preparations in western blots. Overall, the genome sequence and organization of BRRV is more similar to the caulimoviruses Peanut chlorotic streak virus and Soybean chlorotic mottle virus than to other members of Caulimoviridae.
Non-pathogenic Rhizoctonia species elicit systemic induced resistance to Rhizoctonia solani and Alternaria macrospora in cotton. S. JABAJI-HARE (1) and S. M. Neate (2). (1) Plant Science Dept., McGill University, Montreal, Canada, H9X 3V9; (2) CSIRO, Land and Water, South Australia 5064. Publication no. P-2001-0016-NEA.
We evaluated the biocontrol ability of non-pathogenic strains of Rhizoctonia species (np-R) against root and foliar diseases of cotton, and compared their disease control efficacy with the chemical inducer Bion®. Cotton seedlings pre-treated with np-R gave good protection against pre- and post emergence damping-off caused by R. solani. Seedling stand of protected cotton was significantly higher (P < 0.05) than that of non-protected cotton. Np-R isolates significantly reduced disease severity. Cotton plants treated with Bion® were not protected against rot, but Bion® sprays combined with np-R pre-treatment of cotton provided good protection. Significantly less A. macrospora leaf spots occurred on cotyledons pretreated with np-R or sprayed with Bion®, however the np-R treated seedlings had significantly less leaf spots than Bion®-treated seedlings. The results show that np-R can protect cotton from infections caused by root and leaf pathogens through induced systemic resistance.
Strategies to improve control of leaf blights on processing carrots. S. A. JOHNSTON and M. L. Fogg. Rutgers Agricultural Research & Extension Center, 121 Northville Road, Bridgeton, NJ 08302. Publication no. P-2001-0017-NEA.
Leaf blights caused by Alternaria dauci and Cercospora carotae are important in reducing yield of processing carrots in New Jersey. In 1998 and 1999, experiments were conducted to determine (i)optimum fungicide timing using chlorothalonil and (ii)efficacy of the fungicide azoxystrobin, applied alone or in alternation with chlorothalonil. Fungicide applications were made every 10 days or according to TOM-CAST using either an 18 or a 35 DSV threshold. In 1998, 3 less fungicide applications were made with TOM-CAST, and in 1999, 2 less applications were made using the 18 DSV threshold. In both years, chlorothalonil applied according to TOM-CAST(18 DSV threshold only) provided control of leaf blights as effectively as the 10-day schedule. Both application timing methods provided similar yields. Yields were significantly greater than the non-treated check with both application timings in 1999, but only with the 10-day schedule in 1998. Azoxystrobin applied alone or in alternation with chlorothalonil provided significant control of leaf blights and a significant yield increase compared to the non-treated check each year.
Screening spent mushroom substrate (SMS) for microorganisms suppressive to Verticillium fungicola. P. M. LABUSCHAGNE, J. J. Kremser, D. M. Beyer, and P. J. Wuest. Department of Plant Pathology, The Pennsylvania State University, University Park, State College, PA 16802, USA. Publication no. P-2001-0018-NEA.
Spent mushroom substrate (SMS) is a residual product consisting of mushroom compost and peat moss that remains when mushroom crops end. Water leached, pasteurized SMS has potential as casing material for mushroom production. Microorganisms isolated from different SMS sources and commercial peat moss were assayed for siderophore production. Selected microorganisms were tested in vitro for antagonism against Verticillium fungicola, causal agent of dry bubble disease of Agaricus bisporus (button mushroom).
Status of Gremmeniella spp., causal agents of Scleroderris canker. G. LAFLAMME. Canadian Forest Service, Ste. Foy, Quebec, Canada G1V 4C7. Publication no. P-2001-0019-NEA.
Scleroderris canker of conifers is caused by the ascomycete Gremmeniella abietina. The taxonomy of this pathogen has undergone many changes since the discovery of the disease in North America in 1963. In 1975, three serovars, often referred to as races, were recognized for that species. In 1989, a reassessment of the genus was made based on results of morphological, cultural, and biochemical studies. Thus, in addition to the var. abietina representing the three serovars, the var. balsamea was proposed for the pathogen infecting spruces and balsam fir in Canada. New information on the epidemiology of the fungus infecting different hosts, in combination with results of sequencing the isolates representative of the host range of the disease provides a better understanding of this disease on its respective hosts. A review of the taxonomy of G. abietina is proposed that will include at least two new species.
The interaction of Rhizoctonia fragariae and Pratylenchus penetrans in strawberry black root rot. J. A. LAMONDIA. Dept. Plant Pathology and Ecology, Connecticut Agricultural Experiment Station, Windsor, CT 06095. Publication no. P-2001-0020-NEA.
Black root rot is a complex disease of perennial strawberry caused by Rhizoctonia fragariae and the lesion nematode Pratylenchus penetrans. R. fragariae was commonly isolated from healthy perennial roots, diseased structural roots, and P. penetrans lesions. Pathogen interactions were studied in split-root crowns divided in half and placed in separate pots. There were four treatments. For the first two, crowns were inoculated with R. fragariae or P. penetrans in one set of roots (the other was left uninoculated). For the third, R. fragariae and P. penetrans were added to separate halves of the same root system, and for the fourth, both pathogens were added to the same half of the root system. Treatments were replicated five times and the experiment was repeated twice. Treatments had no effect on shoot weight after 10 weeks, but root weights were reduced by both pathogens. Root rot was greater for crowns infected with both pathogens in the same pot than when pathogens were inoculated separately or individually. The interaction of R. fragariae and P. penetrans appears to be local rather than systemic.
The dynamics of mefenoxam insensitivity in a recombining population of Phytophthora capsici characterized with AFLP markers. K. H. LAMOUR and M. K. Hausbeck. Dept. of Botany and Plant Pathology, Michigan State University, East Lansing, MI. Publication no. P-2001-0021-NEA.
Recent findings suggest that recombination may play a role in the survival and evolution of mefenoxam sensitivity (MS) in populations of Phytophthora capsici in Michigan. In 1998, 63 mefenoxam insensitive isolates were recovered from a field with a history of mefenoxam use. In 1999, 200 isolates and in the spring of 2000, 34 isolates were recovered from untreated squash fields at this location. Isolates from 1998 and 1999 were characterized using amplified fragment length polymorphism (AFLP) markers and all isolates were screened for compatibility type and MS. In 1998, 92%, and in 1999, 71% of the isolates had unique AFLP genotypes with no identical isolates recovered between years. Fixation indices for 37 polymorphic AFLP loci indicates little differentiation between years. The frequency of the mefenoxam insensitivity allele was 0.91 in 1998, 0.84 in 1999, and 0.93 in 2000. We conclude that oospores play a key role in survival and that the mefenoxam insensitivity allele may not decrease once mefenoxam selection pressure is removed.
Two transposons from the chestnut blight fungus, Cryphonectria parasitica. D. Linder-Basso and B. I. HILLMAN. Department of Plant Pathology, Rutgers University, New Brunswick, NJ 08901-8520. Publication no. P-2001-0022-NEA.
Two transposons have been identified in the nuclear genome of the chestnut blight fungus, Cryphonectria parasitica. The first element identified was a class II transposon of the hAT family of Activator (Ac)-like transposons. This element, named Crypt1, is 3,563 bp, including 21 bp inverted terminal repeats. Unique 8 bp direct repeats flanking Crypt1 were identified in each of three clones examined. A single large ORF with the potential to encode a putative transposase of 946 amino acid residues was deduced from the sequence of Crypt1. Crypt1 is closely related to the Ac-like transposon Tascot from the ascomycete Ascobolus immersus. Transposition of Crypt1 was inferred from Southern blots of laboratory-maintained C. parasitica isolates, but transposition appears to be a rare event. A second transposable element of less than 2 kb, which was most closely related to the Fot1 element from Fusarium oxysporum, was recently identified. The Fot1-like element appears to have accumulated to higher copy numbers in most C. parasitica isolates than Crypt1.
Susceptibility to bacterial wilt and attractiveness to cucumber beetles varies among cucurbit crop types and cultivars. M. T. MCGRATH. Dept. of Plant Pathology, LIHREC, Cornell Univ., Riverhead, NY 11901. Publication no. P-2001-0023-NEA.
A comparison of cucurbit crop types and cultivars was conducted in 1999 under natural infestation of diabroticite beetles (striped and spotted cucumber beetles), vector of Erwinia tracheiphila (causal agent of bacterial wilt). The ornamental gourd 'Turk's Turban' was very attractive to beetles and susceptible to wilt, with most plants severely wilted on 9 Jul, 22 days after beetles were first observed. Only 8% of gourd 'Pear Bicolored' were wilted on 15 Jul. Generally, cultivars with the most beetles/plant and the most feeding damage had the highest incidence of wilt. However, while the pumpkins 'Harvest Moon' and 'Howden' had higher beetle infestations than 'Merlin' (1-1.3 vs. 0.4 beetles/plant on 6 Jul), they had lower wilt incidence (3, 13, and 89% of these plants, respectively, developed severe wilt by 25 Aug). Wilt incidence was higher in cucumber than muskmelon. All summer and zucchini squash cultivars examined developed wilt. Watermelon 'Crimson Sweet' and winter squash 'Waltham Butternut' did not develop wilt although beetles and their feeding damage were seen. Other winter squash cultivars were susceptible.
Managing resistance to demethylation inhibiting (DMI) fungicides in cucurbit powdery mildew. M. T. MCGRATH and N. Shishkoff. Dept. of Plant Pathology, LIHREC, Cornell University, Riverhead, NY 11901. Publication no. P-2001-0024-NEA.
Field-grown muskmelons were treated with various fungicide programs in a replicated experiment in 1999. The main objective was to evaluate two strategies for managing resistance: 1) tankmixing a DMI (triadimefon, T) with a multi-site fungicide having low risk for resistance (chlorothalonil, C), and 2) alternating a DMI with another at-risk fungicide with a different mode of action (azoxystrobin, A). T was used because resistant strains already occur. A newer DMI, myclobutanil (M), was also used. Frequency of T-resistant strains on abaxial leaf surfaces was 20% before treatment. After 5 applications, it was 80% for T, 0% for C, 50% for T + C, 33% for A alternated with T, 0% for A alternated with T + C, 0% for A alternated with M + C, and 14% for nontreated. Severity of powdery mildew on abaxial surfaces on 24 Aug was 46, 61, 40, 5, 17, 3, and 84% respectively. Severity due to resistant strains was 37, 0, 20, 2, 0, 0, and 12% respectively. In conclusion, while strategy 2 was more effective than 1, C did contribute to managing DMI resistance on abaxial surfaces where spray deposition and thus mildew control is poor compared to adaxial surfaces.
An improved methodology for characterizing novel phytoalexins from Cucumis sativus L. D. J. MCNALLY, C. Labbé, and R. R. Bélanger. Centre de Recherche en Horticulture, Département de Phytologie, Université Laval, Québec, Qc, Canada G1K 7P4. Publication no. P-2001-0025-NEA.
Until very recently, lignification and the induction of enzymes were thought to be the only mechanisms used by cucurbits as means of protection against fungal pathogens such as powdery mildew. New research suggests that glycosylated phytoalexins may play a more important role in the defense strategy of this family of plants. However, the fact that they are produced in such minute quantities, and the lack of a reliable methodology have made the study of these compounds very difficult. The objectives of this work were to (1) develop a simple, reproducible method of inducing, extracting, and purifying phytoalexin compounds; and (2) use this methodology to identify novel phytoalexins from cucumber plants. Using this improved methodology, the structures of three phenolic acids previously described as phytoalexins in other cucumber cultivars were characterized, as well as two novel induced flavonoid c-glycosides. These results validated this new methodology, and reinforced the findings of earlier studies reporting phytoalexin activity within this family of plants.
Inorganic and organic salts: a potential alternative for the control of Fusarium dry rot of potato. M. R. MECTEAU, J. Arul, and R. J. Tweddell. Centre de Recherche en Horticulture, Pavillon de l'Envirotron, Université Laval, Québec, Canada, G1K 7P4. Publication no. P-2001-0026-NEA.
Dry rot, caused by Fusarium sambucinum, is one of the most important diseases of stored potatoes. The objective of this study was to evaluate the postharvest application of inorganic and organic salts as an alternative method for the control of potato dry rot. The effect of different salts on mycelial growth, sporulation, and spore germination of F. sambucinum was evaluated in vitro. To determine the effect of salt application on dry rot development, wounded tubers were dipped in salt solutions before or after inoculation with F. sambucinum. Results showed that aluminum salts, potassium sorbate, sodium benzoate, sodium phosphate (tribasic), and sodium metabisulfite inhibited completely mycelial growth, sporulation, and spore germination of F. sambucinum. In addition, it was demonstrated that aluminum chloride, applied as a curative treatment, decreased dry rot severity whereas disease severity was reduced by preventive applications of sodium carbonate and sodium metabisulfite.
Quorum sensing control of the CPS virulence determinant in Pantoea stewarti, the disease agent of Stewart's wilt disease in corn. T. D. MINOGUE (1), M. Wehland (2), F. Bernhard (2), and S. Beck von Bodman (1). (1) University of Connecticut, Storrs CT; (2) Freie Universitaet Berlin, Berlin Germany. Publication no. P-2001-0027-NEA.
Pantoea stewartii causes Stewart's wilt on sweet corn as a result of vascular occlusion by the bacterial capsular polysaccharide (CPS). CPS synthesis is controlled at two levels. Primary control derives from EsaR-mediated quorum sensing regulation, which couples CPS synthesis to cell growth. Secondary regulation requires transcriptional activation by the RcsA/B transcription complex. Our genetic results indicate that EsaR functions as a repressor, and that strains mutated in the esaR gene are capable of synthesizing large amounts of CPS independently of cell density and acyl-homoserine lactone co-inducer. Interestingly, mutant strains expressing CPS in a deregulated manner are significantly less virulent than the wild type strain. Here, we present biochemical data that support a function for EsaR as a repressor of quorum sensing. We employed electrophoretic mobility shift assays and Biacore surface plasmon resonance to evaluate the DNA binding properties of EsaR for a 20-mer lux box like element in the esaR promoter. In addition, circular dichroism and fluorescence spectroscopy established that AHL binding promotes structural changes in EsaR. These studies support our genetic data. We will discuss a model for EsaR function as a repressor in contrast to related proteins that are signal dependent transcriptional activators.
Occurrence of pine wilt disease caused by Bursaphelenchus xylophilus on Scots pines in central New York State. N. A. MITKOWSKI. Dept. of Plant Pathology, NYSAES, Cornell University, Geneva, NY 14456. Publication no. P-2001-0028-NEA.
Bursaphelenchus xylophilus, the pine wood nematode, is endemic to the United States. In the Northeast, disease occurrence is sporadic and frequently only manifests itself in stressed hosts. In Central New York, Scots pine (Pinus sylvestris L.) is most frequently affected by the disease. During the Spring of 2000, numerous Scots pines began to wilt and die in several stands within Seneca County. Symptoms were typical of pine wilt disease. To confirm the presence of the pine wood nematode, trees were sampled in July from 5 different stands. A total of 23 trees were sampled. Extracted nematodes were consistent with earlier descriptions of B. xylophilus. Of the trees sampled, 70% of the Scots Pines were infected with detectable levels of B. xylophilus. 10% of the total pines observed exhibited pine wilt symptoms at the time of sampling. All extracted female nematodes belonged to the strain of B. xylophilus possessing rounded tails, the only strain known to cause pine mortality. We speculate that the dry conditions of 1999 and an infestation of the pine shoot beetle play a significant role in contributing to this current outbreak.
Potential use of spore sampling to help initiate fungicide applications against potato late blight. V. PHILION (1) and O. Carisse (2). (1) IRDA, St-Hyacinthe, Qc J2S 7B8; (2) CRDH, St-Jean, Qc J3B 3E6. Publication no. P-2001-0029-NEA.
Potato late blight is a devastating disease and its control requires many fungicide applications. However, current Disease Warning Systems (DWS) do not consider inoculum availability for the initiation of sprays. In 1999 and 2000, a Burkard 7-day volumetric spore trap and rotating impact volumetric air samplers (RIVAS) were used in untreated potato plots at two locations to monitor the airborne concentration of sporangia at canopy height. Sporangia concentration rose sharply at least one week before symptoms became detectable. Daytime sporangia concentration was related to disease progress in the field and increased from disease onset; it reached 1200 sporangia/m(^3) at the epidemic inflection point, and finally decreased to background levels when the plants died. Daytime trapping accounted for 84% of the total number of sporangia. Since sporangia were detected at least a week prior to symptom detection with a simple RIVAS, it may be possible to integrate inoculum concentration into a DWS to help initiate sprays. Field application of this approach would require the development of a sampling kit and validation on a larger scale.
Penicillium expansum invades Empire apples through stems during long term controlled atmosphere storage. D. A. ROSENBERGER, C. A. Ahlers, and F. W. Meyer. Dept. Plant Pathology, NY Agric. Exp. Stn. (Geneva), Cornell University's Hudson Valley Lab, Highland, NY 12528. Publication no. P-2001-0030-NEA.
To determine if Penicillium expansum can invade apple fruit through stems, mature Empire apples were collected from the same six orchards in each of two years and were inoculated by placing 500 spores of P. expansum on the end of each stem within eight hours after harvest. Half of the inoculated fruit were held in CA storage (1C, 1.6% oxygen) for at least six months and the other half were held in cold air storage at 2C. During two years of testing, 39% of all inoculated fruit developed stem-end decay in CA storage whereas less than 1% of fruit decayed in cold air storage. Incidence of stem-end decay during CA storage ranged from 3% to 65% depending on orchard source. Levels of boron in fruit and leaves were positively correlated with increasing susceptibility to decay (R(^2) = 0.69). Boron levels in leaf samples ranged from 29 to 46 mg/kg of leaf dry weight. This is the first report that P. expansum can invade apples through stems during CA storage and the first evidence that susceptibility to decay is correlated with boron concentrations in fruit.
Prevalence of conidia of Penicillium species on apple bins and in packinghouse air. D. A. ROSENBERGER, C. A. Ahlers, and F. W. Meyer. Dept. Plant Pathology, NY Agric. Exp. Stn. (Geneva), Cornell University's Hudson Valley Lab, Highland, NY 12528. Publication no. P-2001-0031-NEA.
To determine how inoculum of Penicillium expansum is dispersed, concentrations of airborne conidia were monitored in three apple packinghouses on eight dates during the 1999-2000 packing season. Agar plates exposed in a Burkard air sampler were incubated at 2C for 45 days to allow selective growth of the Penicillium species (mostly P. expansum) that cause apple decays. Less than 10 spores/L of air were detected on four sampling dates in November and December compared to a mean of 68 spores/L on four sampling dates from February through April. Spore loads on empty wooden storage bins (360 kg net capacity) were estimated by washing empty bins and making dilution plates of the wash water. As many as 800 million spores per bin were released into the wash water. Spore loads on bins were reduced 99.8% by washing bins with a commercial quaternary ammonium sanitizer. Spores that recycle from year to year on bins contribute to selection pressure for resistance to postharvest fungicides and may be the primary source of inoculum for infecting each new crop of apples.
Protectant and postinfection activity of SI and strobilurin fungicides against apple scab, powdery mildew, cedar apple rust, and quince rust. D. A. ROSENBERGER, F. W. Meyer, and C. A. Ahlers. Dept. Plant Pathology, NY Agric. Exp. Stn. (Geneva), Cornell University's Hudson Valley Lab, Highland, NY 12528. Publication no. P-2001-0032-NEA.
Protectant and postinfection activities of fungicides were tested on mature Jerseymac and Ginger Gold apple trees. Trees were at petal fall on May 10 and were in the midst of the spring growth flush when the first fungicides were applied on 22 May. Major infection periods occurred 9-10 May, 12-13 May, and 18-21 May. Test treatments were applied on 22 May just prior to appearance of symptoms from the infections incurred 9-10 May. All plots were retreated with mancozeb on 31 May, then left unsprayed for the remainder of the season. The SI fungicide treatments (fenbuconazole and myclobutanil-plus-mancozeb) controlled cedar apple rust and suppressed quince rust but the strobilurin fungicides (kresoxim-methyl and trifloxystrobin) did not. All the treatments were equally effective for protecting new leaves from apple scab, but myclobutanil had less postinfection activity than trifloxystrobin and kresoxim-methyl. Myclobutanil provided the best control of mildew.
Antifungal activities of two essential oils in the prevention of mildew infection (Blumeris graminis) in wheat (Triticum spp.). A. SCALA, S. Overton, M. Zitka, and D. Ryan. Bergen County Academies. Publication no. P-2001-0033-NEA.
Essential oils are distillation extracts that give a distinctive flavor and fragrance in plants. These oils, terpenes, and oxygenated compounds offer antiviral, antibacterial, antifungal, and repellent effects. The current experiments were designed to see if the oils from patchouli (Pocostemon cablin) and eucalyptus (Eucalyptus globules) decrease the incidence of powdery mildew in 3-4 week old wheat plants. Entire plant surfaces were sprayed with soybean oil as a control or test oil before and during mildew infection to evaluate the fungicidal potential of the oil. Although preventative treatments appeared negative, therapeutic effects yielded promising results including >90% reduction in colony formation of the 160 potted plants examined. Each pot measuring 3" × 3" × 3" included 15-20 individual wheat plants.
Distribution of cucurbit powdery mildew races 1 and 2 on watermelon and muskmelon. N. SHISHKOFF and M. T. McGrath. Dept. of Plant Pathology, LIHREC, Cornell University, Riverhead, NY 11901. Publication no. P-2001-0034-NEA.
Cucurbit powdery mildew on watermelon (Citrullus lanatus) is a new disease in the US which has been increasing in importance. Because this coincides with increased reports of race 2 in the US, mildew isolates from watermelon and other hosts in 7 states (TX, MD, NY, AZ, CA, FL, and GA) were assayed to determine which race was responsible for watermelon infections. Isolates were inoculated onto leaf disks from muskmelon (Cucumis melo) cultivars used as race differentials ('Topmark', 'Hale's Best', 'PMR-45', 'PMR-6') and onto leaf disks of watermelon 'Crimson Sweet'. Of 24 isolates from watermelon, two were race 2. The 45 isolates from muskmelon were equally divided by race, and 26 would grow on watermelon (10 of which were race 2). Fifteen isolates from pumpkin and squash (Cucurbita pepo) of both races would not grow on watermelon leaf disks.
Evaluation of chemical and biological fungicides for the control of bentgrass dead spot. G. W. TOWERS and B. B. Clarke. Dept. of Plant Pathology, Rutgers University, New Brunswick, NJ 08901. Publication no. P-2001-0035-NEA.
Bentgrass dead spot (BDS), incited by the fungus Ophiosphaerella agrostis, is a new disease of creeping bentgrass greens and tees. Fungicides were evaluated for their ability to control BDS on a naturally infested golf course green. Fungicides representing ten different chemical classes were applied at various rates and intervals. Data were collected for disease severity, turf quality, and algal cover. Fungicides within the benzimidazole, dithiocarbamate, nitrile, phenylpyrrole, and phosphonate classes provided the most effective control of BDS (78-97% control, compared to untreated turf). Of the sterol-inhibiting fungicides, only propiconazole adequately controlled BDS (95% control), whereas myclobutanil and triadimefon proved ineffective at the rates tested. Similarly, two experimental strobilurin fungicides (BAS 500 and 505) consistently suppressed BDS (96-97% control), while the strobilurins trifloxystrobin and azoxystrobin provided poor to fair control (3 and 72% control, respectively) of BDS. Carboximide and phenylamide fungicides, and a strain of Bacillus subtilis, did not significantly control BDS.
Monitoring of gray leaf spot epidemics in golf courses in New England, New Jersey, and Pennsylvania in 2000. W. UDDIN (1), G. L. Schumann (2), G. Viji (1), and S. H. Boyd (3). (1) Dept. of Plant Pathology, The Pennsylvania State University, University Park, PA 16802; (2) Dept. of Microbiology, University of Massachusetts, Amherst, MA 01003; (3) Hydros, Inc., Falmouth, MA 02540. Publication no. P-2001-0036-NEA.
Epidemics of gray leaf spot in perennial ryegrass turf, caused by Pyricularia grisea, were monitored in CT, MA, NJ, NY, PA, and RI from June to September, 2000. Turf samples were collected from 20 sites (ten each in New England and NJ/PA) biweekly in June and July, and weekly in August and September. Samples were tested for P. grisea using a monoclonal antibody and by microscopic observation of fungal sporulation. Pyricularia grisea was not detected in any samples collected in June and July. Gray leaf spot was first confirmed on 3 Aug 2000 in southeastern PA, followed by a series of epidemics in south-central PA, northeastern PA, southern NJ, and eastern PA during August. The disease was eventually confirmed from all but one site in the NJ/PA survey. Gray leaf spot was not detected in any samples from the survey sites in New England. Further temporal and spatial studies of gray leaf spot epidemics in the northeastern U.S. will be conducted.
Impact of water volume, nozzle type, and clipping removal on the efficacy of trifloxystrobin and other selected fungicides for the control of brown patch in cool-season turfgrass. E. N. WEIBEL and B. B. Clarke. Dept. of Plant Pathology, Rutgers University, New Brunswick, NJ 08901. Publication no. P-2001-0037-NEA.
The efficacy of selected fungicides was assessed for the control of brown patch (Rhizoctonia solani) during 1999 and 2000 using different application methodologies and cultural practices. In the first study, trifloxystrobin (TS) was evaluated at 0.231 kg ai ha(^-1) on a bentgrass fairway in a factorial design using 207, 414, 828, 1,655, and 3,310 L H(2)O ha(^-1) and three nozzle types: flat fan (FF), rain drop, and turbo flood jet. Azoxystrobin (AZ) at 0.309 kg ai ha(^-1) and chlorothalonil (CT) at 6.9 kg ai ha(^-1) were also evaluated at the same water volumes (WV) using a FF nozzle only. In the second study, TS was applied to tall fescue at a rate of 0.154 and 0.386 kg ai ha(^-1) and clippings were either returned or removed. For each year of the study, disease control was independent of nozzle type. The 207 L WV consistently resulted in the least disease control. WV above 207 L H(2)O ha(^-1) provided similar levels of brown patch control. When FF nozzles were used, AZ was more effective than CT or TS in suppressing brown patch. Returning treated clippings improved disease control up to 49%.
Occurrence of Pasteuria-infected Tylenchorhynchus in golf course putting greens. R. L. WICK and B. Dicklow. Dept of Microbiology, University of Massachusetts, Amherst, MA 01002. Publication no. P-2001-0038-NEA.
Twenty-one soil samples received from putting greens for routine nematode assays were also examined for Pasteuria-infected Tylenchorhynchus nematodes. All of the Tylenchorhynchus in each soil assay were examined. All 21 samples had Pasteuria-infected Tylenchorhynchus. On average 26% of juveniles were infected (0-82.%); 40% of males (0-83%), and 40% of females (0-89%). A severity index (SI) was also calculated (total Pasteuria cells visible on cuticle divided by the total number of Tylenchorhynchus in the sample). Avg. SI for juveniles was 1 (0-2.9), females, 4 (0-10.6), and males, 3.6 (0-14.4). An additional putting green was comprehensively sampled (20 soil cores assayed separately, 2934 Tylenchorhynchus). Juveniles had statistically lower incidence of infection (28.8%) than males (64.45%) or females (56.66%). SI for juveniles, males, and females was 1.0, 1.94, and 1.25, respectively. Both Tylenchorhynchus and Pasteuria populations had a clumped distribution in the putting greens. Research is underway to determine if Pasteuria affects nematode population dynamics of Tylenchorhynchus in putting greens.
Postharvest application of organic and inorganic salts for the control of potato tuber soft rot. E. S. YAGANZA, J. Arul, and R. J. Tweddell. Centre de Recherche en Horticulture, Université Laval, Québec, Canada G1K 7P4. Publication no. P-2001-0039-NEA.
Soft rot is the most important bacterial disease affecting the potato industry worldwide. In temperate regions, this disease is mainly caused by the bacteria Erwinia carotovora pv. carotovora and Erwinia carotovora pv. atroseptica. Potato soft rot is presently controlled to a certain extent by cultural and sanitation practices, since there are no efficient chemicals available for this purpose. The objective of this study was to assess the effectiveness of postharvest application of organic and inorganic salts for controlling potato soft rot. The effect of selected salts on bacterial growth and viability was first evaluated in vitro. The impact of their application as dip treatment (200 mM) on soft rot development was then evaluated using artificially-infected tubers. Results show that aluminum chloride, sodium metabisulfite and sodium benzoate completely inhibit bacterial growth and are effective in reducing the severity of soft rot on infected tubers.
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