RESISTANCE IN WHEAT TO COCHLIOBOLUS SATIVUS, A CAUSE OF COMMON ROOT ROT

Abstract

Resistance in wheat to Cochliobolus sativus, the main cause of common root rot in cereals, was shown to be a heritable character. Crosses were made between Thatcher, McMurachy, Willet, 492 (P.I. 94562-1), and 182 (PI. 4309), all of which have shown some resistance to C. sativus but can become heavily infected. The crosses gave rise to both highly resistant and highly susceptible lines that were consistent in their root-rot reaction at four or five locations over 2 years. A simple, practical method was evolved to determine the root-rot reactions of lines and it was basic to their selection. It relies upon natural field infections and is oriented to obtain a high level of disease of the plants. The pedigree method of plant breeding was used to overcome the problem posed by the tendency for many plants to escape infection. Isolations of organisms from lesions gave assurance that the observed resistance was for C. sativus and not for Fusarium spp., which may also cause common root rot. A simplified disease rating was used to record data on the basis of two classes, essentially, resistant and susceptible.