Race non‐specific resistance of oats to primary infection by mildew

Abstract

SUMMARY A range of oat species, species hybrids and derived addition lines, varied in their level of race non‐specific resistance to mildew. This resistance prevented attempted primary penetration by a proportion of spores. It was generally expressed more strongly in fifth than in first formed leaves and thus appeared to be a component of adult plant resistance. Penetration was most frequently arrested at the infection peg stage, implicating the papilla formed by the host as a defence mechanism. Epidermal cells close to stomata were more commonly invaded than others, but only in two of ten lines examined was preferential stomatal subsidiary cell infection observed. Where penetration was successful, host resistance could operate by arresting infections prior to the establishment of functional host/pathogen relations. In hybrids between resistant wild species and a susceptible cultivated oat, the level of both forms of resistance was reduced, indicating a similar effect of the susceptible host genome on genes conditioning both resistances.