Flax rust resistance involving the K gene: an ultrastructural survey

Abstract

An electron microscopic study of major gene resistance involving the flax K gene and the rust fungus Melampsora lini revealed several interesting ultrastructural features. Up to 9 days after infection, most haustoria-containing resistant host cells appeared viable. During this period there was a progressive increase in a fibrillar deposit in the extrahaustorial matrix which was not detected in the susceptible host. This material was in direct continuity with the distal wall of the haustorial neck. It frequently constituted an apparently complete layer or 'encapsulation' around the haustorium and was present in 75% of the extrahaustorial matrices as early as 4 days after infection. Initially, callose-like encasements formed around only a small percentage of haustoria in the resistant host; however, by day 9, about 20% of the haustoria were encased. No encasements were found around susceptible haustoria at this stage. Hypersensitive host cell collapse occurred in a small percentage of resistant infections.