Components of the tan spot disease cycle
1998
Francl, L.J. (North Dakota State Univ. Fargo (USA). Dept. of Plant Pathology)
The disease cycle of wheat tan spot is being studied both as a model system to test new information technology and as a means to better understand the epidemiology of this economically important disease. Inoculation, infection, and conidial liberation and dispersal were assessed in the field with a mobile bioassay. Inoculation, conidiation, and liberation were examined in growth chambers and using a crude wind tunnel. Pyrenophora tritici-repentis normally conidiates diurnally, but conidiogenesis proceeded in culture at 13oC in constant light and on moist wheat leaves at 20oC in constant darkness. Fewer conidia were formed on diseased areas of leaves subjected to interrupted wet periods than on constantly wet leaves, which bore 22 conidia mm-2 after 96 h. The rate of conidial liberation was lower than expected from studies on detached leaves. While conidia are relatively large, they may be dispersed further than 10 km in turbulent air flow. Conidiophores were about 4 percent as infective as conidia, and mycelium was largely uninfective when susceptible plants were exposed to a 24-h wet period after experimental inoculation. In North Dakota, environmental conditions conducive to natural inoculation often coincided with a suitable infection period. Dew periods after intermittent rains were conducive to tan spot development, and inoculum potential was much greater after flowering than before. Artificial neural networks, a novel mathematical processing strategy, outperformed statistical regression techniques and discriminated daily tan spot infection periods with as much as 87 percent accuracy. Neural networks thus appear well suited for disease forecasting.
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