A LOCAL-LESION TECHNIQUE FOR MEASURING THE INFECTIVITY OF CONIDIA OF BOTRYTIS FABAE SARDINA

Discrete lesions developed when conidial suspensions of Botrytis fabae Sardina were rubbed with the forefinger on leaves of broad bean plants (Vicia faba L.) subsequently kept in a water-saturated atmosphere. The numbers of lesions which developed were directly proportional to the concentration of inoculum. At equal concentrations, conidia from young cultures produced more lesions than conidia from old cultures. Variation in lesion numbers between plants within a pot always considerably exceeded the variation between opposite half-leaflets of a leaf, as did variation between pots and between leaves of old, but not of young plants. As the standard error of the number of lesions developing per half-leaflet (x) increases as the mean increases, the values of x need to be transformed before being statistically analysed. A suitable transformation is z = log(10) 1/2{x + c + root(x(2) + 2cx)}, where c = 20.