April 6-11, 2003 - South Padre Island, Texas
(Joint with the APS Southern Division, Latin American Association of Plant Pathology, and Mexican Society for Plant Pathology)
Posted online April 25, 2005
Spatial dynamic of pepper wilt. G. AVILA-QUEZADA (1), A. A. Gardea (1), A. Pedroza-Sandoval (2), H. Silva-Rojas (3), and S. P. Fernandez-Pavia (4). (1) Centro de Investigacion en Alimentacion y Desarrollo, Delicias, Mexico; (2) Univ. Autonoma Chapingo, Durango, Mexico; (3) Colegio de Postgraduados, Montecillo, Mexico; (4) IIAF, Univ. Michoacana de San Nicolas de Hidalgo, Morelia, Mexico. Publication no. P-2005-0001-CRA.
P. capsici causes pepper (C. annuum) wilt as a result of crown and root rot and can eventually kill the plant, causing significant losses for pepper growers over the world. The amount of rainfall and irrigation frequency can have strong effects on the development of the disease and on disease spread. Three commercial fields of jalapeño pepper in Chihuahua, Mexico, were monitored over time to characterize the spatial progression of wilt, and to obtain evidence of inoculum dispersal mechanisms. Spatial dynamic was determined using LCOR2 analysis. Isolates were obtained from diseased pepper plants to identify the causal organisms. Quadrats containing either one dead or wilted plant were autocorrelated in each field. Autocorrelation of wilted or dead plants was greater within than across rows in all fields, and in some evaluation dates it occurred undirectionally for long distance, which suggests the importance of water movement along rows on disease spread. Extensive crop and drainage of surface water containing inoculum, could be responsible for the disease pattern and progression, and the water movement could be the cause of the kind disease spread identified by autocorrelation. Final disease incidence was low (1.4%) in one field, and high (20-27%) in two fields. P. capsici, Fusarium sp. and Rhizoctonia sp. were isolated.
Characterization of Phytophthora ipomoeae in the central highlands of Mexico. G. BADILLO-PONCE (1), S. P. Fernandez-Pavia (2), N. J. Grünwald (3), E. Garay-Serrano (4), G. Rodriguez-Alvarado (2), and H. Lozoya-Saldaña (5). (1) ICAMEX, Metepec, Mexico; (2) IIAF, Univ. Michoacana de San Nicolas de Hidalgo, Morelia, Mexico; (3) USDA ARS, Prosser, WA; (4) IFIT, Colegio de Posgraduados, Montecillo, Mexico; (5) Depto. de Fitotecnia, Univ. Autonoma Chapingo, Chapingo, Mexico. Publication no. P-2005-0002-CRA.
Several wild species of the genus Ipomoea grow in the central highlands of Mexico, some of which show blighted leaves and petioles. Blighted tissue of Ipomoea was collected in four regions of the central highlands of Mexico, and a total of 27 Phytophthora ipomoeae Flier & Grünwald isolates were obtained. Isolates were characterized for oospore production in vitro from single cultures grown on rye agar, genotypic diversity for the isozymes Peptidase (Pep) and Glucose 6-phosphate isomerase (Gpi), metalaxyl resistance (5 ppm) and DNA fingerprint (on selected isolates). Twenty two isolates were obtained from I. orizabensis (Pelletan) Ledeb. ex Steud (I. thyrianthina Lindl., I. longepedunculata (Mart. & Gal.) Hemsl.) and 5 from a different Ipomoea species that is reported for the first time as a host for P. ipomoeae. All isolates produced oospores and were sensitive to metalaxyl. Four multilocus genotypes were determined, the genotype 78/78 for Pep and 108/108 for Gpi was the most frequently found. A new genotype 78/78 (Pep)/96/108 (Gpi) isolated from I. orizabensis is reported. Polymorphism was not detected using the P. infestans probe RG-57.
Ozone alternative for the control of Anthracnose in mango fruits. M. C. BARBOSA (1), G. L. Ponce de León (1), C. Pelayo-Zaldivar (1), and D. Nieto-Angel (2). (1) División de Ciencias Biológicas y de la Salud, Universidad Autónoma Metropolitana-Iztapalapa. Av San Rafael Atlixco 186. C.P. 09340 México D.F., México; (2) Instituto de Fitosanidad, Colegio de Posgraduados. Km. 35.5 Carr. México-Texcoco, Montecillo Edo. de Méx. C.P. 56230. Publication no. P-2005-0003-CRA.
The infection of Colletotrichum gloeosporioides known as Anthracnose (A) is one of the main diseases of tropical fruits including mangoes. In order to evaluate the effectiveness of ozone in the control of A, spores of infected tissues were isolated and pure cultures were obtained. Three experiments were conducted. In the first one, spores were exposed to 0.8 and 2.0 mg/L ozone concentrations during 15 min and germination was quantified. In the second one, mangoes var. ‘Haden’ and ‘Manila’ were inoculated by sprayed with solutions of spores and the development of symptoms evaluated. Finally, inoculated fruits with A development in course were treated with ozonized water (2,0 mg/L) and the development of symptoms evaluated. The results indicate that: ozone in concentrations of 0.8 and 2.0mg/L applied to spores reduces the germination to less than 2%. The presence of visual symptoms were delayed and diminished in 20 and 30% in mangoes inoculated with spores treated with ozone. The development of A is not arrested in inoculated mangoes treated with ozonized water 12 h after inoculation. The variety ‘Manila’ is more susceptible to the infection than ‘Haden’. It was confirmed that the application of ozone does not alter the quality of the fruits and represents an alternative technology to the use of fungicides for the control of A.
Survival of Phytophthora infestans sporangia exposed to solar radiation in the Toluca Valley. C. R. BELMAR-DIAZ (1), N. J. Grünwald (2), S. P. Fernández-Pavía (3), E. Garay-Serrano (4), G. Romero-Montes (3), G. Rodriguez-Alvarado (3), and H. Lozoya-Saldaña (5). (1) PICTIPAPA, Metepec, Mexico; (2) USDA ARS, Prosser, WA; (3) IIAF, Univ. Michoacana de San Nicolas de Hidalgo, Morelia, Mexico; (4) IFIT, Col. de Posgraduados, Montecillo, Mexico; (5) Depto. de Fitotecnia, Univ. Autonoma Chapingo, Chapingo, Mexico. Publication no. P-2005-0004-CRA.
Aerial dispersal of sporangia of Phytophthora infestans (Mont.) de Bary are the most important means of spreading potato late blight and initiating and maintaining epidemics. Solar irradiance is one of the weather variables that influence survival of sporangia during the dispersal process. Sporangia obtained from sporulating lesions on potato leaves and transferred to membrane filters were exposed to solar irradiance in Metepec, Mexico located in the Toluca Valley. Sporangia were subjected to one of the following treatments (during different time periods): direct exposure to sunlight, protected from direct radiation, or not exposed at all (maintained on top of a lab bench). The treatments were conducted during the summer on sunny and cloudy days. Viability decreased faster when sporangia were exposed to direct sunlight than when protected from direct radiation. No differences were observed between cloudy and sunny days. Sporangia do not survive more than 40 min of exposure; this period is shorter than what has been reported for other locations. Solar irradiance influences survival of sporangia of Phytophthora infestans in the Toluca valley.
Infectious clones of Melon chlorotic leaf curl virus, a previously undescribed begomovirus in the Squash leaf curl begomovirus clade. J. K. BROWN and A. M. Idris. Department of Plant Sciences, University of Arizona, Tucson, AZ 85721 USA. Publication no. P-2005-0005-CRA.
Melon chlorotic leaf curl virus (MCLCV) is a new, previously undescribed begomovirus affecting melon crops in Zacapa Valley, Guatemala. The first epidemic in which this virus was recognized as a new begomovirus species occurred in 2000, and all fields throughout the valley were 90-100% infected. Symptoms of the disease are severe leaf curling and shortened internodes in muskmelon and honeydew melon, and fruit spotting and cracking in honeydew melon. Provisional identification was accomplished by polymerase chain reaction (PCR) amplification, cloning, and sequencing of the core region of the coat protein gene (533 bp). Comparison of the core CP sequence with the analogous sequences available in Genbank for well-studied begomoviruses revealed less than 82% nucleotide (nt) identity, suggesting the occurrence of a new begomoviral species, provisionally, MCLCV. The virus was cloned from DNA extracts purified from field-infected melon. Phylogenetic analysis for the DNA A component revealed the closest relatives to MCLCV are SLCV and Squash mild leaf curl virus (SMLCV) (previously SLCV-R) at 82 and 78% nt identity, respectively. Analysis of the DNA B component indicated SLCV and SMLCV were most closely related to MCLCV at 60 and 65% nt identity, respectively. Collectively, results suggest that MCLCV is a new, previously undescribed begomovirus species. Preliminary analysis to detect recombination between MCLCV and its five closest relatives in the SLCV clade revealed no significant potential sites of recombination.
Coffea arabica resistance to Ceratocystis fimbriata in advanced progenies of Caturra × Borbon crossing. C. B. L. CASTRO (1) and G. H. A. Cortina (2). (1) Department of Plant Pathology and (2) Department of Plant Breeding, Colombian National Coffee Research Center, CENICAFE. Chinchiná, Colombia, P.O. Box 2427 Manizales, Colombia. E-mail: BerthaL.Castro@cafedecolombia.com. Publication no. P-2005-0006-CRA.
Stem canker of coffee plants, due to the fungus Ceratocystis fimbriata, causes important losses in Colombian coffee-growing regions. In order to get a commercial coffee cultivar resistant to C. fimbriata, plantlets and adult plants of 13 F5 progenies derived from the cross between the Coffea arabica varieties Caturra and Canker Resistant Borbon, were evaluated for their resistance and agronomic behavior. First, the most pathogenic isolate was selected among 30 C. fimbriata isolates collected from Caturra plants in the colombian coffee region. Next, resistance was determined early on 9 month old plantlets, and then on adult plants. Resistance was evaluated by the suberized area around the pathogen lesion, the longitudinal and transversal advance of the lesion, and by plant mortality. The Caturra cultivar was used as susceptible control. An isolate that caused 100% mortality on Caturra was used as inoculum at a concentration of 2 × 10(^4) ascospores/ml, which was deposited on a wound on the plant stem. On plantlets, 8 progenies exhibited high resistance, 2 were moderately resistant and 3 were moderately susceptible. In adult plants, and 30 months after inoculation, 7 progenies exhibited high resistance, with 7% mortality; 3 progenies were moderately resistant, and 5 were moderately susceptible. All Caturra plants died. The seven highly resistant progenies exhibit Caturra dwarfness, good agronomic and cup qualities and could be used to control coffee canker by the Colombian growers.
Sugarcane yellow leaf virus spread in Florida. J. C. COMSTOCK and J. D. Miller. USDA-ARS, Sugarcane Field Station, 12990 Highway 441, Canal Point, FL 33438 USA. Publication no. P-2005-0007-CRA.
Sugarcane yellow leaf virus (SCYLV), the cause of leaf yellows of sugarcane, is a threat to the industry in Florida. The incidence of SCYLV infected sugarcane plants averaged 89% for 15 grower fields (sampling 100 plants per field comprising 8 cultivars). In the CP-variety development program, plants germinated from true seed were virus free but the incidence of SCYLV increased with exposure to natural infection. After 3 years in the CP-variety development program the incidence of SCYLV was 30.1% in the 4705 Stage II clones tested from 1998 through 2002. After three years additional exposure, the incidence of SCYLV in the 61 clones that were selected and advanced to Stage IV was 55.6%. Only 10 clones (testing 40 plants each) at this stage had an incidence of SCYLV below 25% and only one clone tested negative for the virus. Presently, no selection pressure is placed against clones having SCYLV in the program but this will probably change. Plants of meristem-tissue-culture derived seedcane were initially free of the virus. However, the incidence of virus due to natural infection increased in plants after two years exposure to natural infection of five cultivars monitored with differences ranging from 20 to 86% infection. The use of virus free seedcane may be a useful control practice especially in clones where the virus spreads slow.
Corncobs harbor inoculum of Aspergillus flavus in South Texas. R. JAIME-GARCIA and P. J. Cotty. USDA-ARS-SRRC, 1100 Robert E. Lee Blvd., New Orleans, LA 70124. Publication no. P-2005-0008-CRA.
Aspergillus flavus causes aflatoxin contamination in both cottonseed and corn. Cotton/corn rotations are common in South Texas where reduced tillage frequently results in long-term residence of corncobs on soil surfaces. Corncobs are colonized by A. flavus either prior to harvest or in the soil. This study sought to determine the potential of corncobs as sources of inoculum for cotton and corn in South Texas. Corncob and soil samples were collected from 24 fields extending from Calhoun and Victoria Counties in the north to the Rio Grande Valley during the planting seasons of 2001 and 2002. In addition, A. flavus communities in corncobs and soil were contrasted in two fields on a biweekly basis for one season. Results indicate that corncobs might be an important source of A. flavus inoculum for cotton and corn crops. Corncobs from the previous season contained, on average, over 100 times more A. flavus propagules than soil from the same field, and two-year old corncobs still retained 50 times more propagules than soil. There were no significant differences in incidences of A. flavus strain S between corncobs and soil. The quantity of A. flavus in corncobs decreases with corncob age.
Soil solarization and Larrea tridentata extract as a biocontrol agent on root damage and epidemiology of pepper plants. R. H. LIRA-SALDIVAR (1), J. Cruz B. (2), F. D. Hernández C. (2), A. Flores O. (2), G. Gallegos M. (2), and F. Jiménez D. (3). (1) Centro de Investigación en Química Aplicada. Saltillo, Coah., 25100; (2) Universidad Autónoma Agraria Antonio Narro. Saltillo, Coah., 25315; (3) Campo Experimental La Laguna, Matamoros, Coah. 27000. México. Publication no. P-2005-0009-CRA.
Four dose (0, 10, 20 and 40 kg ha(^–1)) of L. tridentata extract incorporated to solarized and nonsolarized plots was evaluated on incidence and disease severity of soilborne pathogens. Treatments were assessed for incidence of naturally occurring root pepper pathogens. An inhibitory effect on disease severity was observed by solarization alone, since the untreated control plots reported 120% increase on root damage compared to solarized plots. Solarization treatments amended with 20 kg ha(^–1) L. tridentata extract presented slight root damage, but solarization alone reported a 134% increase in root damage severity. R. solani and Phytium sp. CFU were significantly higher in untreated plots, though colonies of F. solani and A. alternata remained high in treated plots; therefore, these pathogens appeared to be more tolerant to solarization and L. tridentata extract. Bare soil amended with 20 kg ha(^–1) extract reported an increase of 567% on root damage compared to solarized treatments with 20 kg ha(^–1) of the extract. Pepper yield was significantly increased with solarization in comparison to control plots. Solarization amended with L. tridentata extract appears to be an effective and environmentally friendly method of soil disinfestation.
Mycelial growth inhibition of phytopathogenic stramenopila and fungi by Larrea tridentata extracts. R. H. LIRA-SALDIVAR (1), R. G. López C. (1), L. A. Villarreal C. (1), F. D. Hernández C. (2), and F. Jiménez D. (3). (1) Centro de Investigación en Química Aplicada, Blvd. Enrique Reyna Hermosillo # 140, Saltillo, Coah. 25100; (2) Universidad Autónoma Agraria Antonio Narro, Saltillo, Coah. 25315; (3) Campo Experimental La Laguna, Matamoros, Coah. 27000. México. Publication no. P-2005-0010-CRA.
Leaf extracts from L. tridentata (gobernadora or creosote bush) were investigated using inhibition bioassays; foliage was collected from Coahuila and Zacatecas in a portion of the Chihuahuan Desert and from Baja California Sur, located at the Sonoran Desert. L. tridentata resin was extracted with MeOH, EtOH, CHCl(3) and NaOH. Mycelial growth of stramenopila (Pythium sp. and Phytophthora infestans), and fungi (Rhizoctonia solani, Alternaria solani, Alternaria alternata and Fusarium oxysporum) were severally affected with all extracts. The inhibitory effect was consistent with all solvents used for extraction. MeOH extracts from both deserts had a notable effect because at 500 µl l(^–1) mycelial growth of Phytium sp., and P. infestans did not occur. With 8000 µl l(^–1) all pathogens except F. oxysporum exhibit complete inhibition. After concluding the assays inoculums were transferred to fresh medium and the pathogens did not grow, indicating the in vitro effect. Our results suggest that L. tridentata extracts could be of practical use as antimicrobial compounds of low or nil environment impact and they have important commercial and industrial considerations; hence, in planta studies are now required for this work to progress.
Elicitation of defense response genes in Sorghum bicolor (L.) Moench in response to infection by Fusarium thapsinum and Curvularia lunata at anthesis. C. R. LITTLE (1) and C. W. Magill (2). (1) Dept. Biology, The University of Texas - Pan American, Edinburg, TX 78541; (2) Dept. Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77845-2132. Publication no. P-2005-0011-CRA.
Grain mold of Sorghum bicolor is one of the leading constraints for the production of optimum quality sorghum grain worldwide. Panicles were inoculated at anthesis with conidial suspensions of Fusarium thapsinum and Curvularia lunata to test for induction of defense response genes in spikelet tissues at several timepoints after flowering. Four PCR fragment clones, phenylalanine ammonia-lyase (PAL1-1), chalcone synthase (CHS2G), beta-1,3-glucanase (GLUC2-1) and chitinase (CHIT25-1) were tested and showed increased expression after inoculation of spikelet tissue with fungi. Accumulation of red-pigmented compounds and increased mRNA levels for PAL1-1 and CHS2G indicated that the phenylpropanoid and flavonoid pathways were induced by inoculation, but greater induction did not associate with resistance indicating that this pathway is not solely responsible for defense against grain mold. Defense genes appeared to be elicited non-specifically.
Genetic variability of Fusarium oxysporum f. sp. ciceris strains in Mexico using PCR-RAPD. A. Luna-Paez (1), E. VALADEZ-MOCTEZUMA (1), H. V. Silva-Rojas (2), and N. Marban-Mendoza (3). (1) Universidad Autonoma Chapingo, Departamento de Fitotecnia. Texcoco, Mexico C.P. 56230; (2) Colegio de Postgraduados, Programa de Semillas-IREGEP, Montecillo, Mexico C. P. 56230; (3) Universidad Autonoma Chapingo, Departamento de Parasitologia Agricola. Texcoco, Mexico C.P. 56230. Publication no. P-2005-0012-CRA.
The chickpea, Cicer arietinum, is affected by different pathogens that reduce yields. Fusarium oxysporum is among the most important. The symptoms of affected plants involve wilting and yellowing. There is a lack of information on genetic variability and distribution of Fusarium oxysporum in Mexico; thus the main purpose of this contribution was to estimate the genetic variability of 41 isolates from F. oxysporum f. sp. ciceris using DNA polymorphism detected with PCR-RAPD technique. Chickpea plants showing disease symptoms were collected at 22 localities in the states of Guanajuato and Michoacan. The Bainbridge et al. (1990) protocol was used to extract DNA. The random primers selected were C-01, C-08, C-11, and C-14 from Carl Roth Company. The amplified fingerprints were very clear and reproducible and so were able to detect DNA polymorphism. The data from the isolates were grouped in seven clusters using UPGMA and Dice coefficient. This clusters confirms the genetic variability of F. oxysporum f. sp. ciceris at this Bajio area.
Efficacy of methyl iodide on Rhizoctonia solani, Meloidogyne incognita and yield in tomato. R. T. MCMILLAN (1), H. H. Bryan (2), and J. J. Sims (3). (1) University of Florida, Homestead, FL; (2) TREC; (3) University of California, Riverside, CA. Publication no. P-2005-0013-CRA.
Montreal Protocol of 1991 and its 1992 amendment categorized methyl bromide as an ozone depletion chemical and required that all production, importation and use of substance in US must be phased out by 2005. Methyl iodide (TM-42501) a nonionizing chemical was selected to determine effectiveness for control of soil borne plant pathogens. Four soil fumigants were evaluated for control of soil-borne Rhizoctonia, and root-knot nematode, and fruit yield: TM-425 + Chloropicrin at 300 lb and TM-425 + Chloropicrin + methyl-bromide at 300 lb, TM-425 at 100-lb, TM-425 at 175-lb, Telone C35 at 35-gal and Chloropicrin (PIC) at 137-lb per acre. A field trial was installed on January 29, 2002 at a site on sandy loam soil in Central Florida. Soil beds were formed 48-in wide on 6-ft centers. Each plot was 500-ft long, replicated five times. Fumigants were injected through three shanks, 9-in apart, at depth of 4-in with 1.5-mil polyethylene film placed over the beds. After 7 days plastic was perforated to allow venting and 12 days later tomato cultivar ‘Asgro Florida 47’ transplants were planted at spacing of 24-in in row on March 29, 2002. All of the fruits were harvested from 30 plants/plot. Following fruit harvest 10 plants/plot were pulled for root evaluation. TM-42501 plus Chloropicrin, TM-42501, and Methyl bromide plus Chloropicrin provided statistically significant control or root rot and root knot nematode as compared with untreated control. TM-42501 plus Chloropicrin, TM-42501, and Methyl bromide + Chloropicrin provided significantly more large fruit compared with control.
Soil nematodes associated to onion seedlings in the Morelos state of Mexico. M. Mundo-Ocampo (1), R. M. Belmont (2), R. N. Juárez (2), and H. E. F. Moctezuma (2). (1) Department of Nematology, University of California Riverside; (2) Centro de Desarrollo de Productos Bióticos, Instituto Politecnico Nacional, Proyecto CONACYT 36601-B. Publication no. P-2005-0014-CRA.
Traditional onion production in the Morelos state of Mexico involves two steps. Seeds beds are usually established on small selected areas. Forty five days old seedlings are then transplanted into fields to complete their production cycle. Soil born diseases may be distributed under this cultivation practice. Soil born diseases incidence and distribution was observed and recorded during the period of development of seedlings before transplanting. In addition, soil nematode population diversity and distribution in four main onion production localities of the state has been estimated. Several plant parasitic nematodes, including Spiral nematodes (Helicotylenchus spp., Aorolaimus sp.); Stunt nematodes (Tylenchorhynchus spp.); Lesion nematodes (Pratylenchus spp.); Reniform nematode (Rotylenchulus reniformis) and the Cyst nematode (Cactodera sp.), were identified in most sampled sites. Saprophytic soil nematodes including Acrobeles, Cephalobus, Cervidellus, Pseudacrobeles, and the mycophagous nematode Aphelenchus avenae are also present in considerable population densities. Identification to species is currently in progress. This study will provide useful information on nematode diversity and distribution on the traditional sustainable onion cropping system in the Morelos state of Mexico.
Status of begomoviruses (Geminiviridae) and economically important whiteflies in Guatemalan in 2001. M. Palmieri (1), M. E. Méndez (1), D. Rogan (2), A. M. Idris (2), and J. K. Brown (2). (1) Institute of Research, Plant Protection Dept., Univ. del Valle of Guatemala, Guatemala; (2) Dept. of Plant Sciences, Univ. of Arizona, Tucson, AZ 85721 USA. Publication no. P-2005-0015-CRA.
Begomoviruses transmitted by Bemisia tabaci (Genn.) continue to limit crop production in Guatemala. In 2001, a study was undertaken to determine the identity and distribution of begomoviruses and economically important whitefly species there, including haplotypes or biotypes of B. tabaci. Symptomatic plant samples and whiteflies were collected at varying altitudes along transects in the eastern, western, and southern regions. At least 16.4% of samples showed begomovirus symptoms, of which 85% were tomato and pepper, and 15% were cucurbit species. Identification was based on BLAST or CLUSTAL W analysis of whitefly and begomovirus sequences, by comparison with analogous sequences available in public databases. DNA sequences were obtained for the begomoviral core coat protein gene (core CP) or the whitefly mitochondria cytochrome oxidase (mtCOI) gene using polymerase chain reaction (PCR) and degenerate primers, respectively. The two most predominant whitefly species identified in crops and weeds were Trialeurodes vaporariorum (>1000 msnm) and B. tabaci (<1000 msnm). For B. tabaci, both indigeneous haplotypes and the exotic B biotype, introduced from the Eastern Hemisphere, were associated with crop and weed species. Several previously described and at least five unreported begomoviruses were identified in crop and weed species. Collectively, these data are essential to designing management strategies to control whitefly vector populations and begomovirus diseases in Guatemala.
Morphologic and molecular characterization of Colletotrichum falcatum causal agent of the red rot in sugarcane. F. RAMIREZ-CERVANTES, J. F. Gómez-Leyva, A. Brena-Becerril, M. P. de Loza-Macias, M. E. Villalobos-Alcalá, J. Mora-Galindo, and L. A. De la Cruz-Cevallos. Instituto Tecnológico Agropecuario de Jalisco, Tlajomulco de Zúñiga, Jal., México AP. 12. Publication no. P-2005-0016-CRA.
C. falcatum is a deuteromicete fungus of the Melanconiaceae family, distributed in tropical and subtropical regions of Mexico and the world where sugarcane is grown, causing important economic losses. In this work, the sexual and asexual cycles of C. falcatum were determined in vitro using transmission electronic microscopy, as well as the intracellular and intramural subcuticular hemibiotrophic infection mechanism in vitro. Amplifying the PCR region of rDNA ITS1-ITS2, the amplified product of 576 bp was cloned and sequenced (GenBank No AF487427). The restriction analysis using the Acc I and Ava I showed unique fragments of C. falcatum, making it possible to separate C. falcatum from other related species. We have identified 20 nucleotide primers (cf1) that appear to be specific for C. falcatum and not present in other fungi. Amplification through PCR produce segments of C. falcatum rDNA of 400 bp. We are currently analyzing by means of PCR assays infected samples of cane in order to determine the distribution of C. falcatum in Mexico.
Screening maize lines for resistance to downy mildew Peronosclerospora sorghi (Weston & Uppal). C. G. Shaw, L. E. Sánchez (1), A. D. GONZÁLEZ (2), J. M. Alezones (2), V. R. Barrientos (2), and A. A. Chassaigne (2). (1) Universidad Nacional Experimental del Táchira, Estado Táchira, Venezuela, Apdo. 436, web site: http://unet.edu.ve; (2) Fundación Danac, Estado Yaracuy, Venezuela, Apdo. postal 182, website: www.danac.org.ve, e- mail: email@example.com. Publication no. P-2005-0017-CRA.
Techniques used for screening maize genetic resistance to Downy mildew at field conditions is a relatively tedious and expensive procedure that limits the numbers of genotypes tested. Therefore the identification of possible sources of resistance is an important matter. For that reason a controlled inoculation scheme was developed to detect resistance in maize under controlled conditions. In this study we include 80 maize inbred lines maintained by DANAC. Additionally a highly susceptible check (F-2002) was included to assure the efficiency of the inoculation method. The technique consists of an inoculation procedure with conidia of P. sorghi at 17°C and 99% of RH in an inoculation room, followed by a greenhouse incubation period (21 days). After that, the seedlings are evaluated for % of plants infected and severity of the injury. The technique allowed us to determine important differences between genotypes. Non parametric Kruskal & Wallis analysis showed differences between genotypes. At the same time we detect a group of resistant lines (D10, D11, D17, D20, D32, D35, D55, D57, D71 and D80) to be used by the breeding program. Due to the high levels of damage of the susceptible check and several other entries we conclude that the technique is efficient to induce symptoms and identify genetic resistance in maize.
Factors affecting oospores germination of Albugo occidentalis. M. A. TRENT, J. P. Damicone, and S. von Broembsen. Dept. Ento. & Plant Path., Okla. State Univ., Stillwater, OK 74078. Publication no. P-2005-0018-CRA.
Oospores germination of Albugo occidentalis, the casual agent of spinach white rust, has not been previously described. Oospores were extracted from leaves and agitated in water on a rotary shaker at 23°C. A limited number (<10%) germinated by forming a vesicle that released two or four zoospores. Effects of temperature (17, 23, or 29°C), additive (soil, root and leaf extracts), and agitation (+/-) on germination were evaluated. Germination, expressed as zoospore production/100 oospores, was greater at 23 (7.7) and 29°C (11.4) than at 17°C (0.4). Leaf and root extracts increased zoospore release (13 and 6.5, respectively), compared to the control (3.9). Zoospore production was greatest at 44 and 68h with maximum release at 52h (25.3). There was no effect of agitation on zoospore production; however, there was a significant agitation × time interaction. Maximum zoospore production occurred at 60h with agitation (38.5) compared to 76h without agitation (42.1). Results indicated that oospores germination.
Defense response in common bean genotypes that are resistant to Apion godmani Wagner. B. Utrillo-Sanchez (1), C. Jacinto-Hernández (2), A. Richards (1), and E. SORIANO (1). (1) Instituto de Investigaciones Químico Biológicas. U.M.S.N.H. Apdo. Postal 50-3. Morelia, Mich. México 58070; (2) CEVAMEX-INIFAP, A.P.10, Chapingo, México 56230. Publication no. P-2005-0019-CRA.
Common bean defense response include phytoalexin accumulation, with phaseollin. When bean pods are infested with Apion godmani W., the amount of phaseollin accumulated in elicited pods was lower in bean genotypes susceptible to ovoposition than those resistant, suggesting that the presence of the insect inhibited the bean pod defense response. In this work, bean plants were elicited to compare phytoalexin accumulation as related to behaviour towards the insect ovoposition in the field. (Phaseolus vulgaris L.) genotypes: cvs. Mex-332, J-117, Amarillo-155 (insect-resistant) and Canario-155, Bayomex and Desarrural (insect-susceptible) were grown in vermiculite in an incubating chamber. Seven day old plants were inoculated with an elicitor solution to measure phaseollin levels. The genotypes that in the field behaved as susceptible to insect ovoposition were capable of accumulating phaseollin, with the genotype Desarrural accumulating twice as much phaseollin as the control. On the other hand, in the insect-resistant bean genotypes, except in J-117 there was also phaseollin accumulation; moreover, Mex-332 accumulated ten times as much as Amarillo-155. This suggests that there is not correlation between susceptibility to insect ovoposition and lack of defense response in bean genotypes.
Wheat blast occurrence in Paraguay. L. Q. Viedma. Centro Regional de Investigación Agrícola, Dirección de Investigación Agrícola, Ministerio de Agricultura y Ganadería, Km 16, Ruta VI, Capitán Miranda, Itapúa, Paraguay. Publication no. P-2005-0020-CRA.
Wheat blast, caused by (Pyricularia grisae Sacc., syn. P. oryzae Cav.), was detected on wheat fields in Paraguay, for the first time, causing damage to the crop in 2002 cycle. Disease was more severe in the Department of Itapúa, south of the country, especially in Pirapó, La Paz, Alborada and Colonias Unidas locations. Less incidence was observed in southern Alto Paraná Department. The predominant symptom was spike bleaching. Grain yield of infected fields decreased up to 80% and spike samples showing symptoms ranged from 30 to 70%. The high disease incidence was associated to early sowing (end of April and first two weeks of May) with high temperatures and humidity at ear emergence. Fungicides trials carried out on 2002, indicates that mixtures of triazol & strobilurines applied at spike emergence could be an alternative of control.
Comparison of DNA/RNA ratios in healthy and Tinangaja-infected Cocos nucifera leaflets. G. C. WALL and A. T. Wiecko. CALS/AES, University of Guam, Mangilao, GU, 96923. Publication no. P-2005-0021-CRA.
Ultraviolet spectrophotometric analysis was used to study the ratios of DNA and RNA in total nucleic acid extracts of healthy and Tinangaja-infected leaflets of Cocos nucifera L. Samples were collected from top, middle and bottom portions of the canopy in 30 previously assayed trees from three different locations on the island of Guam: Deans Circle (UoG campus), Mangilao village, and Tiyan. Total nucleic acids were extracted with CTAB solution after tissues were macerated by hammering at room temperature. Presence or absence of CTiVd, the causal agent of Tinangaja, was verified by 2.5% agarose gel electrophoresis. Statistical analysis of data (SuperAnova, Abacus Concepts, Berkeley, CA) revealed differences between locations for the 260/280 angstrom ratios obtained with a Beckman DU530 spectrophotometer; the ratio was lower for the Deans Circle location than for the others. Additionally, there was a tendency for ratios to be lower in the bottom canopy and higher in the top canopy of diseased trees, while in healthy trees the tendency was the opposite.
Non-persistence of ergot on sorghum in Mississippi. N. Zummo and L. E. Trevathan. Dept. of Entomology and Plant Pathology, Mississippi State University, Mississippi State, MS 39762. Publication no. P-2005-0022-CRA.
Ergot (sugary disease caused by Sphacelia sp.) of sorghum (Sorghum bicolor) was identified on selected male-sterile cultivars at several locations in Mississippi in 1997. The disease was also widespread in commercial sorghum plantings throughout the state. When the differential male-sterile cultivars were replanted at the same locations in 1998, sugary disease was found only at one location. Traces of sugary disease were found only in a few commercial plantings. Plantings of male-sterile sorghum lines and commercial sorghum plantings since 1999 throughout Mississippi remained free from disease. The survival of Sphacelia sp. since 1997 was not determined.