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Abstracts of Presentations at the 1989 Annual Meeting of the American Phytopathological Society

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Abstracts of Presentations at the 1989 Annual Meeting of the American Phytopathological Society Abstracts of Presentations at the 1989 Annual Meeting of The American Phytopathological Society August 20-24, 1989 Richmond Marriott Hotel and Richmond Convention Centre Richmond, Virginia The number above an abstract corresponds to its designation in the program of the 1989 APS Annual Meeting in Richmond, VA, August 20-24. If a presentation was not given at the meeting, the abstract is not printed among the following pages. The index to authors begins on page 1224. 1 lated peanut leaf and disease proportions are generated for early leafspot, late leaf spot, both leafspots mixed or peanut INFLUENCE OF TILLAGE SYSTEMS ON THE INCIDENCE AND SPATIAL PAT- rust. Pre-testing, drill and practice, and post-testing sessions TERN OF TAN SPOT OF WHEAT. Wolgang Schuh, Department of Plant were conducted in a 1-hr time period for introductory plant Pathology, The Pennsylvania State University, University Park, pathology students. Twenty of 22 students significantly improved PA 16802. their ability to estimate disease proportions of late leaf spot (random lesion sizes) as measured by (i) a higher coefficient of The incidence and spatial pattern of Pyrenophora tritici- determination relating the actual proportion (X) to the esti- repentis was assessed at four locations (two conventional & two mated value (Y) and/or (ii) a regression coefficient (slope) conservation tillage) two times during 1987 and three times which was closer to 1.0 in post-tests compared to pre-tests. during 1988. Tan Spot was detected earlier in 1988 and had a higher final disease incidence in both years under conservation tillage. Spatial pattern analysis, using Morisita's index of 4 dispersion, revealed a shift from clumped to random distribu- EFFECTS OF MAIZE INTERCROPS ON ANGULAR LEAF SPOT OF BEANS. M tion over time, indicating the importance of residueborne eFFECTSOF MAItE ULArsity of oF Kenya. inoculum under conservation tillage systems. Spatial patterns Boudreau, Crop Science Dept., University of Nairobi, Kenya. under conventional tillage were random, indicating airborne inoculum iment suggestas the source of infection. Results from this exper- Angular leaf spot (ALS) severity was evaluated that straw residue on the field surface will lead which hind been planted alone and simultsneously onwith common maize beans at tincreased thatlstofaPyresidueora therfieldci- to increased levels r faenti t llery Kabete, Kenya in Novembet 1986, and at Kabete and Thika of Pyrenophora tritici-repentis, thereby 1987. Intercropping reduced the area under the disease progressin April counterbalancing advantages associated with the use tillage systems. of reduced cuvcurve (AUDPC)ADC byy2%i 26% in 198696ada and at Thikahk inn18 1987 byy2% 24%, butu did not significantly reduce AUDPC at Kabete in 1987. Additional treatments evaluating bean density and row versus random 2 planting in 1986 had no effect on AUDPC, but fertilizer amendment in 1987 increased AUDPC by 64% at Kabete and 22% at TOBACCO GROWTH AS AFFECTED BY MELOIDOGYNE INCOGNITA AND SOIL Thika. Modifications in temperature, relative humidity, and wind MOISTURE. T. A. Wheeler, K. R. Barker, and S. M. Schneider, velocity in the bean canopy when maize was present suggest Department o-Tit Pathology, North Carolina State University, conflicting influences on ALS development. The results Raleigh, NC 27695-7616. corroborate other data indicating a significant but variable effect of maize intercrops on reducing ALS. Flue-cured tobacco (var. NC27-NF) was grown in microplots in a RCB design with a factorial arrangement of treatments. The main effects werq initial nematode population levels (0 to 20000 5 eggs/500 cm- soil) and irrigation rates (none, low, moderate and high). Plants were destructively sampled throughout the growing A GENERALIZED STOCHASTIC SIMULATION MODEL OF THE INCREASE AND season. All stages of M. incognita were removed from the roots SPREAD OF ARTHROPOD-ECTORED PLANT VIRUSES. and soil at each sampling date. Tobacco with a moderate R.S.F~riss and P. H. Berger. University of Kentucky, Lexington, KY 40546 and irrigation rate had the highest growth rate (r=0.00899), University oflIdaho, Moscow, ID 83843. followed by low and no irrigation (r=0.00709 and 0.00679, respectively). The r parameter is from the logistic equation: A theoretical model was developed for illustration of the effects of virus transmission dH/dt=r*Ht (I-Ht) , where H=host leaf weight and time is in characteristics and vector activity on virus disease dynamics. The model simulates spread from degree-days. Tobacco yield potential was greatly impacted by a source plant in a 425-plant field. Input parameters include probabilities of virus acquisition irr igation rate. Yield suppression by N. incognita was and inoculation, lengths of latent periods in the plant and vector, length of the vector adequately fitted by quadratic regression. infectious period, number of vectors per plant, and three options for the type of simulation of vector movement. Decisions about acquisition, inoculation and vector movement are based on 3 pseudo-random values. Output includes numbers of viruliferous vectors and positions of infected plants at each iteration. Model predictions are generally consistent with expected DISEASE . PRO : A COMPUTED PROGRAM FOB EVALUATING ANDIMPROVING A natural spread. The model illustates the great effect that vector movement can have on disease PERSONS ABILITY TO ASSESS DISEASE PROPORTION. F. W. Mutter, Jr. dynamics and spatial distribution, particularly for diseases transmitted ins non-persistent and 0. Worawitlikit, Department of Plant Pathology, University manner. Although themodel will be difficult to fully validate, it provides a logically rigorous of Georgia, Athens 30602. way of integrating knowledge about the many proceases that affect virus disease epidemics. A computer program written in BASIC was developed for the pur- pose of evaluating a persons ability to estimate disease propor- 6 tions. The program is similar to DISTRAIN but allows greater flexibility in the selection of lesion size (small, medium, A CLIMIATOLODGYOFAIRPARCELTRAjECTORIESRjELATDTO'fI}{ large, random mixture) and allows for regression analysis of ATMOSPHERIC TRANSPORT OF PERONOSPORA TABACINA.LM rating performance. A color monitor is used to display a simu- Davis and J.F. Monahan, North Carolina State University, Raleigh, NC 27695 Temperature and wind date from 5-yr of atmospheric soundings were used in Camera-ready abstracts are published as submitted. The abstracts conjunction with an atmospheric transport model to construct a trajectory are not edited or retyped in the APS headquarters office. climatology for the transport of the sporangia of P.. tab~acina. Daily receptor- Vol." 79, No. 10, 1989 1135 oriented trajectories, with the receptor point located in the mountains of North Winter oilseed rape (Brassica napus) grown on 17'000 ha is Carolina, were calculated for April through August and for the annual period. the predominant edible-oil crop in Switzerland. The moat The 12-, 24-, and 48-hr air parcel positions prior to arrival at the receptor point important fungal diseases are caused by Phoma lingam, Alter- were analyzed by examining the plots of the probability density function (pdf). naria sp., Botrytis cinerea and Sclerotinia sclerotiorum. By integrating the pdf over a region of interest the probability that the given Cylindrosporium concentricum, Verticillium dahliae and Pseu- receptor site will receive air parcels from this region can be obtained. Results docercosporella capsellae are rarely found but have the indicate that the probability of the receptor point receiving air parcels from the potential to become more prevalent. tobacco producing region of south Georgia/north Florida, which is a potential Integrated crop management is employed to try to control inoculum source region, increases during the April to August period. This these diseases. It involves measures such as use of resistant increase can be attributed to the strengthening of the Bermuda high pressure cultivars, crop rotation and removal of infected residue. system. Fungicides are considered a last resort. None are registered at present. The identification of resistant cultivars is a top priority in our research. Special nurseries have been established. The potential use of biotechnology for this 7 purpose will be investigated. GENETIC DIVERSITY AND POPULATION STRUCTURE OF THE RICE BACTERIAL BLIGHT PATHOGEN. J. Leach, M. Rhoads, C. Vera Cruzi, F. White, T. Mews, and H. Leung . Dept. of Plant Pathology, 11 Kansas State University, Manhattan, Kansas and lInternational INFECTION OF STRAWBERRY ROOTS BY COLLETOTRICHUM Rice Research Institute, Los Bafios, Philippines. FRAGARIAE AND GLOMERELLA CINGULATA. C. M. Howard, C. A repetitive DNA element pJEL101 isolated from Xanthomonas K. Chandler, and E. E.. Albregts. Univ. of Fla., AREC, campestris pv. oryzae (Xco) was used to determine the popula- Dover, FL 33527. tion structure of Xco in the Philippines. pJELl01, when used Large roots ca 14 cm long were excised from rhizomes to probe EcoRl-digested genomic DNA of Xco isolates, revealed of strawberry plants that had wilted in Florida race-specific restriction fragment length polymorphisms (RFLP). fruiting rields because of anhthacnose crown rot. Of 94 isolates examined, 26 RFLP types were identified. Most Isolations from the thizomes yielded primarily C. of the variability (20 RFLP types) was found in race 1, 2, and fragariae from seedlings that previously had bean 3, which were isolated from lowland
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