There is considerable interest in the development of potato cultivars with durable late-blight resistance due to polygenes. David Spooner, in Potato Biology and Biotechnology, 2007 7.2.2.2 Horizontal resistance Reiter suggests estimation of the leaf drop-retaining capacity as one of the wheat resistance parameters. Varieties with downward leaves covered, in addition, with dense waxy bloom, are less vulnerable to rust, powdery mildew, and leaf spot, than the varieties with horizontal or ascending leaves, since in the former case the infectious drops roll off the leaves. Short-stemmed wheat varieties are very vulnerable to the leaf spot fungi, whose spores are dispersed by water splashes (septoriosis, rhynchosporiosis, etc.), as the distance between the leaves (length of internodes) in such varieties is short. The difference stems from the fact that the drops necessary for infection dry up faster on the leaves of tops-spreading varieties, than in varieties with compact-tops plants. Potato varieties with spreading haulm are less affected by late blight, than compact-tops varieties, though there is no correlation between the potato plant habitus and its vulnerability at artificial inoculation of leaves in laboratory. T Dyakov, V G Dzhavakhiya, in Comprehensive and Molecular Phytopathology, 2007 Plant habitus An infection period is predicted if high (95–100%) relative humidity lasts for more than 10 hours, and growers are then urged to apply chemical sprays immediately. Several leaf spots, such as those caused by the fungi Cercospora on peanuts and celery and Exserohilum ( Helminthosporium) turcicum on corn, can be predicted by taking into account the number of spores trapped daily, the temperature, and the duration of periods with relative humidity near 100%. Information on all these parameters is, of course, very useful in the formulation of recommendations for fungicide applications. More recent refinements in late blight forecasting include, in addition to data on moisture and temperature, information on the level of resistance of the potato variety to late blight and the effectiveness of the fungicide used. From this information weather severity values are calculated, infection and disease severity values are predicted, and recommendations are issued to growers as to when to begin spraying. solani on tomatoes) TOMCAST (for tomato forecaster) for tomato early blight, Septoria leaf spot, and anthracnose and PLAM for peanut leaf spot, moisture and temperature are monitored continuously. Copyright © 1981Ĭomputerized predictive systems have been developed for epidemics of late blight and several other diseases in some such systems, e.g., BLITECAST for late blight ( Fig. The daily severity values are arbitrary values given by the relative humidity–temperature relationship they correspond to the likelihood of infection shown at left and are used to recommend spray schedules with BLITECAST. Relationship of the duration of high relative humidity periods and average temperature during such periods to the likelihood of potato infection by the late blight fungus Phytophthora infestans.
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