Screening for Disease Resistance in Faba Beans
The exposure of disease screening nurseries to severe epiphytotics is essential to detect reliable resistant sources. Artificial production of epiphytotics in these nurseries requires specific techniques to suit specific pathogens.Disease epiphytotics in faba beans are affected by a wide range of factors which are related to; (1) the pathogen, (2) the host, (3) the environment, and (4) cultural practices. Our emphasis however, is placed on those factors which can be artificially manipulated to induce severe epiphytotics, and thus facilitate the detection of reliable sources of resistance.
The general strategy for identification of resistant sources to major faba bean diseases consists of three phases:
Phase 1: This phase deals with germplasm screening to detect genes for resistance to local populations of the pathogen. There are two screening cycles. The first is conducted using a mixed inoculum collected from a wide range of naturally infected faba bean leaves in the locality. The collection of a wide range of isolates to cover all possible pathogenic variabilities in the pathogen is extremely important at this stage. Some resistant sources in the first cycle may develop few sporulating lesions that could be due to unusual, highly virulent pathogenic forms. In order to subject resistant material to a rigorous evaluation, isolates from such lesions are inoculated back,in a second screening cycle, to progenies of the resistant sources detected in the first cycle.
