Effect of Leaf Age, Leaf Segments and Surface Treatments on Pathogenicity Levels of Colletotrichum sublineola in Sorghum and Johnson Grass

Abstract

Colletotrichum sublineola is a casual pathogen of sorghum anthracnose. Sorghum pathologists often need to conduct evaluations for anthracnose resistance in large scale which are expensive and labor intensive. As a solution, an excised-leaf assay has been used, but whether or not leaf age, position or region affects pathogenicity scores has not previously been evaluated. Essentially, in an excised-leaf assay, is response to C. sublineola over all or part of a leaf blade identical? To get an answer, three sorghum and one Johnson grass cultivars were tested. The top five leaves were inoculated at the apex, mid-leaf and base of each leaf blade. Results show nearly no effect of leaf age to pathogenicity level within the top five leaves. Furthermore, in order to evaluate any protective role of leaf wax to C. sublineola, the wax was disrupted by simply wiping the leaf surface by a thumb, or as an alternative method, leaf surface tension was reduced by submerging leaves into 2% TWEEN 20 before inoculation. Compared to control, wiped leaves increased pathogenicity scores on the leaf blade and midrib in two of three sorghum cultivars, but 2% TWEEN 20-treated leaves had only minimal changes in pathogenicity level compared to controls.