Simple and rapid detached leaf technique for screening common beans (Phaseolus vulgarise L.) in vitro against angular leaf spot (Pseudocercospora griseola) disease

A rapid and reliable detached-leaf technique was developed for screening common bean (Phaseolus vulgaris) genotypes against angular leaf spot (ALS) disease caused by Pseudocercospora griseola. It is helpful to differentiate between susceptible and resistance common bean genotypes. Detached leaves of common bean tested genotypes were inoculated by immersing them into a spore suspension followed by placing into petri dishes at room temperature on cotton moistened with tap water. After 10-day incubation, the leaves were monitored for symptom development. This screening method was effective to determine the pathotype of P. griseola isolates on a set of ALS differential common bean genotypes. With this specific screening technique, all known sources of ALS resistance genes, including MEX-54, BAT332, and AND277 exhibited resistant reactions to ALS and showed no reaction and symptom development following inoculation with P. griseola isolates collected from Ethiopia. However, all other common bean genotypes tested together with genotypes known for their susceptibility with reaction scores 4 to 9 developed lesions in the interveinal regions of the leaves. Hence, the proposed simple and rapid screening technique was efficient, low-cost, and able to differentiate between resistant and susceptible common bean genotypes. It can be used for screening in marker-assisted gene pyramiding and backcrossing programs to facilitate early selection of seedlings in segregating progenies. Key words: Detached leaf, Pseudocercospora griseola, genotype screening.