Penetration resistance to Erysiphe pisi in pea mediated by er1 gene is associated with protein cross-linking but not with callose apposition or hypersensitive response

Powdery mildew caused by Erysiphe pisi DC is an important pea disease which causes high yield and quality losses. The most efficient way to control this disease is the use of resistant cultivars. Three genes of resistance are known so far in pea, namely er1, er2 and Er3. The most widely deployed gene in pea cultivars worldwide is er1. Resistance conferred by er1 is complete and considered to be durable, being recently demonstrated that er1 is in fact a member of the mlo gene family. Resistance is caused by colony abortion albeit the responsible cellular mechanisms causing this colony abortion are not known. In this study, the presence of different mechanisms related with colony abortion, such as callose apposition, protein cross-linking and hypersensitive response was quantified in a resistant pea er1 line compared to a susceptible check. Our histological studies showed that protein cross-linking, plays a determinant role in the penetration resistance conferred by er1, whereas callose apposition or hypersensitive response played little role.