Microscopical Studies on Interactions of Host and Non-host Plants with Bean Rust (Uromyces viciae-fabae (Pers.) Schroet)

Abstract

Microscopical investigations were made to examine the interaction between host and nonhost plant species inoculated with U. viciae-fabae. A tissue clearing method was used by overnight exposure of about 1 cm2 cut inoculated leaf tissue in 95 % methanol followed by 4-6 hour in 0.25% chloral hydrate alone and with added Trypan blue. A comparison of infection of hosts and non-host plants by the pathogen showed significant variation (p < 0.01, d f= 13) in the behavior of the fungus on leaf surfaces and there was also a clear difference in intercellular growth. In most non-host and resistant hosts fewer germ tubes have located stomata due to reduced directional growth. From the few located some hyphae were successful in penetrating through the stomata. Among the tested materials, faba bean and pea cvs Kelvedon Wonder, Feltham First and Waverex showed susceptible reactions resulting in sporulation. In contrast to susceptible and resistant hosts, many hyphae stopped growing in leaves of non-host at early stage of intercellular development, except in White clover where the hyphae continued to grow to the stage of haustorium formation. In resistant hosts, except Tufted vetch, the intercellular hyphae continued to grow to the stage of first haustorium formation and sporulation in sweet pea cvs and partially resistant pea cv. Greenshaft, respectively. All resistant plant species showed the hypersensitive response at different stages of disease development. The hypersensitive response of guard cells, epidermal cells, mesophyll cells, and deposition of induced phenolic substances on the walls of infection hyphae and accumulation of such materials on the plant cell walls of the attempted penetration site appeared to restrict further growth of the fungus in plant species showing resistance. The restricted sporulation of this particular isolate of U. viciae fabae in only Viciae faba and Pisum sativum indicates that it has very narrow host range. This in turn indicates that this isolate has very little importance than the one known to infect large number of hosts.