A PRELIMINARY STUDY OF CORN SEEDLING BLIGHT IN SOUTHERN ONTARIO

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Abstract
In southern Ontario, seedling blight is the major factor responsible for poor stands of corn and its gradual decline in yield for the past number of years. This disease expresses itself as an uneven stunting and chlorosis throughout the field. It may be caused by Pythium arrhenomanes Drechs., Pythium debaryanum Hesse., Fusarium moniliforme Sheld., Fusarium graminearum Schw., or Rhizoctonia solani Kuehn. P. arrhenomanes, which is the most economically important pathogen encountered, produces millions of zoospores in moist soil Under natural field conditions, it seldom kills the plant, since corn possesses unusual capacity to send out new adventitious roots when tire causal organism destroys the older roots. In the course of these studies, F. graminearum was found only once and apparently is not important as a soil-borne organism in this corn–wheat-growing area. F. moniliforme was present in most lesions, but it is not an active root parasite and, in the majority of cases, is a secondary invader Studies conducted in refrigerated rooms have shown that temperature has a greater influence on the hosts (wheat and corn) than on the organism, P. arrhenomanes, because disease incidence was greatest at low temperatures for corn and at high temperatures for wheat. Although nematodes are very numerous in necrotic roots, they appear to be of little importance.

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