Analyses Of Slight Incompatibility In A Bean Rust Infection And Its Consequences For Uredospore Production And Viability

An interaction between the Redlands Greenleaf cultivar of Phaseolus vulgaris and the race adhi of Uromyces appendiculatus showed slight incompatibility, seen as a necrotic ring around uredinia. The incompatibility was expressed at 25 °C but not at 21 °C. The incompatibility was compared with the compatibility of the interaction between the cv. Epicure and race gh. Optical and electron microscopy revealed that incompatibility resulted in fewer haustoria and hyphal branches at infection sites 48 h after inoculation, decreased mycelial growth, deposition of material against host cell walls where haustoria had penetrated, vacuolation of mature haustoria, intercellular hyphae and urediniospores, and wider extra-haustorial matrices around mature haustoria. Host cells throughout uredinial colonies had depleted contents, and surrounding cells were collapsed. Urediniospores germinated poorly, germ tubes were less likely to form appressoria, and an inoculum gave rise to few uredinia per unit area of leaf.