Interactions between spot blotch (Cochliobolus sativus) and wheat cultivars.
Screening programmes using wheat wide crosses with Agropyron [Elymus] and wild emmer (Triticum dicoccoides) accessions as sources of resistance to C. sativus are described. Somaclonal variation in resistance was observed in plants regenerated from callus culture. Progress in breeding for resistance has been slow, a result of various factors, including low resistance levels in commercial spring wheats and the wide pathogenicity spectrum of C. sativus isolates. Pathogenicity studies with a global collection of C. sativus monoconidial isolates on a differential set of wheat varieties and lines revealed 15 pathotypes. It was calculated that, for several national isolate collections, 1-2% of the variance is due to interactions and it is assumed that several genes for virulence are operating in the pathosystem. It is concluded that to facilitate studies on the inheritance of resistance to spot blotch, there is a need to monitor, on a global scale, the virulence situation in areas particularly affected by the disease.