Studies on sharp eyespot disease of cereals

SUMMARY Several isolates of Rhizoctonia solani Kühn were obtained from wheat stems bearing lesions of sharp eyespot in the summers of 1960 and 1962. Differences in virulence of these isolates, assessed by severity of attack on seedlings, were demonstrated. Isolates taken from different plants in the same crop were shown to differ in virulence. All isolates obtained from wheat‐stem lesions attacked both winter and spring varieties of wheat, barley, oats and rye. Several varieties of spring and winter wheats showed no differences in susceptibility to disease. Infection of the wheat host took place at any time during the growing period, but was most severe in the earlier stages of growth. Sharp eyespot occurs over a wide range of soil types, but the most severe attacks all occurred on lighter soils with neutral to slightly acid pH. Sand‐culture experiments showed no effect of pH on disease development over the range 5·9‐8·1. Disease development in seedling wheat plants was favoured by cool (9·3°C.) dry ( ca. 20% of the water‐holding capacity) conditions in the greenhouse. Disease incidence in the field over the period 1959‐63 could be correlated with the weather conditions prevailing over this time.