EFFECT OF LONG-TERM CONTINUOUS CROPPING OF SPRING WHEAT ON AGGRESSIVENESS OF Cochliobolus sativus

Abstract
Cochliobolus sativus cultures were collected from symptomatic wheat plants from a plot planted continuously to wheat for over 90 yr and from symptomatic wheat plants in commercial grain fields cropped rotationally in the surrounding area. Pathogenicity of these isolates was tested in replicated greenhouse trials using wheat plants scored for disease 6 wk after inoculation. Isolates from the continuous-cropped wheat plot were more aggressive on average than were isolates from commercial fields. Long-term continuous cropping to wheat appears to shift the population of C. sativus toward more aggressive types, although many less aggressive types also remain.Key words: Aggressiveness, Drechslera sorkiniana, Helminthosporium sativum, wheat root rot

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