Abstract
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.
Highlights
The angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola, infects common bean (Phaseolus vulgaris L.) throughout its centre of origin and domestication range in the Americas, which extends from the Northwest Argentina to Northern Mexico (PastorCorrales et al, 1998)
The detached leaf disease screening method has been reported as an alternative and rapid technique for screening common bean germplasm for resistance against anthracnose disease (Tu, 1986; Pereira et al, 2013) and whit mold (Teran and Singh, 2009). It was reported in soybean by Twizeyimana et al (2007) to screen soybean genotypes for resistance to white-mold disease; the results from the detached leaf assay were reported by the same author and were significantly correlated and comparable with the results of screening house and field screening results
The objective of this study was to evaluate an alternative, simple, low cost and high efficiency in vitro screening technique for common bean genotypes against angular leaf spot caused by P. griseola that could be used in common bean breeding programmes
Summary
The angular leaf spot (ALS), caused by the fungus Pseudocercospora griseola, infects common bean (Phaseolus vulgaris L.) throughout its centre of origin and domestication range in the Americas, which extends from the Northwest Argentina to Northern Mexico (PastorCorrales et al, 1998). The method has been reported for screening wheat for fusarium head blight resistance as an alternative disease screening technique (Browne and Cooke, 2004)
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