Graduate Thesis Or Dissertation
 

Forecasting Pseudocercosporella herpotrichoides foot rot of winter wheat

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/df65vb95j

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  • The use of fungicides for the control of foot rot of winter wheat, caused by Pseudocercosporella herpotrichoides (Fron) Dei., requires a forecast of disease risk to optimize this management practice ecologically and economically. Foot rot occurs in both the mild, wet (100+ cm, ppt./year) annual cropped areas in western Oregon, and the drier (25-50 cm. ppt./year) summer-fallowed areas in eastern Oregon, that have colder winters and warmer summers. Adaptation to the wide range of conditions was examined to deter mine the need for considering ecotypic variation in a forecasting scheme. Although there were isolate differences, no in vitro growth patterns at 5-30°C on KC1 or mannitol osmotically-amended media were indicative of ecotypic variation. The forecasting data base, collected in 1979-80 and 1980-81, included climatological, geographic, agronomic and pathological factors for 39 commercial wheat fields from eastern and western Oregon. The best predictor of end-of-season disease severity from data collected by mid-season, when fungicide applications are made, was the following multiple regression equation: proportion severely infected tillers = -1.08 + 0.04 RSF + 0.20 SDEPTH -0.05 RSPACE where: RSF was a rain score from Sept. to Feb., which relates new infections with amount of daily precipitation; SDEPTH was seeding depth; and RSPACE was row spacing. The variables correspond with macroclimate of new infections (RSF) and microclimate important to disease development (seed date and row space). The model explained 74 percent of the variation in mean disease severity for eastern Oregon-grown Stephens wheat. Several diseases, especially take-all caused by Gaemannomyces graminis var. tritici, confounded foot rot assessments for western Oregon sites and rain score data exceeded values in the model; thus the model was not applicable to western Oregon sites. Minimum yield losses, expected for particular levels of disease severity, were determined as a reference to severity forecasts. Significant (P ≤ .05) yield losses occurred at intervals of approximately 15 percent (10-20) and followed the relationship: percentage yield loss = -1.96 + 0.44 SF where: SF was the percentage of severely infected tillers. Analysis of individual-tiller yield components showed that under conditions of abundant moisture and no lodging, P. herpotrichoides reduced the number of kernels, per head, even with concurrent Septoria spp. head infections that affected both mean kernel weight and number of kernels per head.
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file details GrybauskasArvydasP1983.pdf 2017-08-16 Público Descargar