Interactions of the bean rust and cowpea rust fungi with species of the Phaseolus – Vigna plant complex. I. Fungal growth and development

Abstract

Growth and development of two closely related rust fungi, Uromyces appendiculatus and U. vignae (uredospore infections), were compared in several American and African species of the Phaseolus – Vigna plant complex and in Lablab purpureus. In plants inoculated with U. appendiculatus the frequency of formation of both primary and secondary haustoria generally decreased with evolutionary distance from the American host species. Uromyces appendiculatus formed primary haustoria at a high frequency of infection sites in most American and many African species, and also sustained a limited haustorium – plant cell metabolic relationship (as determined by the amount of secondary fungal growth) in one group of African species. Uromyces vignae generally formed very few haustoria in both American and African species not known as hosts of the fungus; however, growth of U. vignae colonies occasionally continued for some time at a few infection sites in nonhost species without sporulation. The implications of these results are discussed with respect to the coevolution of the two fungi with their hosts.

Early defence responses of cowpea (Vigna sinensis L.) induced by non-pathogenic rust fungi

“…While U. vignae is able to form primary and secondary haustoria and to establish biotrophy, only 8% of the sporelings of U. appendiculatus give rise to haustoria; U. viciae-fabae is not able to form haustoria at all. The latter combinations are typical non-host interactions (Elmhirst and Heath 1987). Demonstration of autofluorescence and phloroglucinol/HCl-positive material in the area of contact between mesophyll cells and haustorial mother cells indicates that lignification could be involved in early defence against rust fungi in both nonhost interactions.…”

Quantitative resistance of flax to flax rust (Melampsora lini)

“…The Linum species showing necrosis may possess genes for hypersensitive resistance that are similar to the major genes that occur in cultivated flax. In the accessions without any signs of infection the resistance may be based on strong prehaustorial defense, as is often seen in nonhost species (Niks 1983, Elmhirst & Heath 1987. Histological studies are necessary to find what defense mechanisms are involved in the resistance of wild Linum species showing no symptoms.…”

“…It is believed that in general the host range of rusts coincides with taxonomie relationship of plants (Savile 1979, Elmhirst & Heath 1987. Six out of the seven susceptible accessions were from the same section as the cultivated flax, section Linum (Table 5).…”

Accumulation of genes for susceptibility to rust fungi for which barley is nearly a nonhost results in two barley lines with extreme multiple susceptibility

“…The majority of these pathogens can only infect one or a few closely related plant species or genera. Resistance shown by all the individuals of a plant species to a specific parasite or pathogen species is known as nonhost resistance (Heath 1981;Elmhirst and Heath 1987). The pathogens involved in nonhost resistance are known as heterologous, inappropriate or nonhost pathogens (called ''heterologous'' in this paper).…”