Evaluating faba beans for rust resistance using detached leaves

A method was developed for testing detached leaves of faba beans for their response to rust disease. Leaves 5 to 8, counting from the shoot tip, were excised and maintained on a water-retaining medium, with 5 ppm gibberellic acid, in an enclosed box in a temperature-controlled glasshouse. Leaves tre ated in this way remained in good health for up to 30 days. Rust spores wer e dispersed in a slurry of talc and water and applied to the abaxial leaf s urface. Disease development of seven rust populations, collected from sever al locations in eastern Australia, was monitored for 15 days on eight faba bean accessions. Four accessions were BPL lines which ICARDA claimed to hav e some resistance, two were ILB lines from ICARDA which had been found to h ave stronger field resistance in northern New South Wales, Australia, and t he remaining two were known susceptibles. The detached-leaf test showed tha t the two cultivars were susceptible, the four BPL lines were intermediate and ILB 3107 and ILB 3025 were slow-rusting. One rust population, which had been stored under liquid nitrogen for several years, was less effective at inducing disease symptoms than the other six, which were all freshly colle cted. The interactions between host accessions and rust populations were st atistically significant but minor, as the cultivars remained in their categ ories of resistance or susceptibility. The detached-leaf technique is thus suitable for use in screening individual plants for reaction to several dif ferent pathogen species or genotypes without danger of cross-contamination or induced resistance.