Evaluating faba beans for rust resistance using detached leaves

Abstract

A method was developed for testing detached leavesof faba beans for their response to rust disease.Leaves 5 to 8, counting from the shoot tip, wereexcised and maintained on a water-retaining medium,with 5 ppm gibberellic acid, in an enclosed box in atemperature-controlled glasshouse. Leaves treated inthis way remained in good health for up to 30 days.Rust spores were dispersed in a slurry of talc andwater and applied to the abaxial leaf surface. Diseasedevelopment of seven rust populations, collected fromseveral locations in eastern Australia, was monitoredfor 15 days on eight faba bean accessions. Fouraccessions were BPL lines which ICARDA claimed to havesome resistance, two were ILB lines from ICARDA whichhad been found to have stronger field resistance innorthern New South Wales, Australia, and the remainingtwo were known susceptibles. The detached-leaf testshowed that the two cultivars were susceptible, thefour BPL lines were intermediate and ILB 3107 and ILB3025 were slow-rusting. One rust population, which hadbeen stored under liquid nitrogen for several years,was less effective at inducing disease symptoms thanthe other six, which were all freshly collected. Theinteractions between host accessions and rustpopulations were statistically significant but minor,as the cultivars remained in their categories ofresistance or susceptibility. The detached-leaftechnique is thus suitable for use in screeningindividual plants for reaction to several differentpathogen species or genotypes without danger ofcross-contamination or induced resistance.