The epidemiology of common root rot in Manitou wheat. III. Development of lesions on subcrown internodes and the effect of added phosphate

摘要

The development of common root rot lesions on subcrown internodes of Manitou wheat was followed in growth-chamber tests. Visible lesions caused byCochliobolus sativusappeared 3 to 5 days after inoculation. The vertical spread of subcrown internode lesions was much faster than the lateral spread; normally, lateral spread did not start until maximum vertical extension had occurred. Considerable variation in rate of development of lesions was evident between individual plants. The overall mean daily rate of vertical extension of subcrown internode lesions was in the range of 0.3 to 0.5ensp;mm. The rate was faster immediately after infection and declined with time. Lesion development on plants generally was more rapid in low-phosphate soil than in high-phosphate soil. This finding was exemplified by higher percentages of severely diseased plants at the end of the experiments; higher probabilities of transfer of plants from less to more severe categories in the intervals between observations; higher disease ratings; and higher mean daily rates of linear extension of lesions in low- than high-phosphate soil. The possible application of some techniques in developing a model for forecasting severity of disease is discussed.