Evaluating faba beans for resistance to ascochyta blight using detached organs

Abstract

Detached-organ techniques were developed, using either individual leaves or stem segments with attached leaves, for use in genetic studies on resistance to ascochyta blight in faba beans. A single isolate of Ascochyta fabae, A26, was used to infect the highly resistant population ILB 752, moderately resistant cultivar Fiord and highly susceptible population NEB 463. Cultural conditions were established that maintained the detached organs in good condition for more than the 10 days required for disease symptoms to be expressed. Detached organs were scored for presence, number and size of lesions and also for number of lesions bearing pycnidia. Spore suspensions of 5 x 10² to 2 x 10⁶ per mL were used, with 5 x 10⁴ providing as much infection as greater concentrations. Leaves and stems were taken from 3-, 5- or 7-week-old plants. Younger plant parts were more susceptible than older ones and plants aged 3–5 weeks provided adequate material for the tests. The susceptibility of the 3 accessions in these experimental conditions followed the order expected from field trials.