Isolation and identification of pathogenic fungi and oomycetes associated with beans and cowpea root diseases in Oman

The purpose of this study was to characterize fungal and oomycete species associated with root diseases ofPhaseolus vulgaris,Vigna unguiculata,V. radiataandVicia fabain Oman. Root samples were collected from plants suffering from weakened growth and yellowing symptoms. Fungal species were isolated on 2.5% potato dextrose agar amended with 10 mg l−1rifampicin and 200 mg l−1of ampicillin and identification was based on sequences of the internal transcribed spacer region of the ribosomal RNA gene (ITS rRNA), glycerol-3-phosphate dehydrogenase (GPDH), translation elongation factor-1 alpha (TEF), beta-tubulin (TUB), calmodulin (CMD), actin (ACT). Isolations yielded 204 fungal isolates belonging to nine different genera, with most isolates belonging toAlternariaandFusarium. Molecular identification revealed that the isolates belong to 20 fungal species, the most dominant of which wasAlternaria alternata. Pathogenicity tests were conducted on each plant species. The inoculations onP. vulgarisrevealed thatPythium aphanidermatuminduced rotting, damping-off and wilt symptoms whileFusarium equisetiinduced yellowing symptoms on the leaves.Rhizoctonia solaniproduced lesions and root rot onVigna unguiculatawhileCurvularia muehlenbeckiaeandCurvularia caricae-papayaeproduced root lesions on the roots ofV. unguiculataandV. radiata, respectively.Alternaria alternataproduced brown symptoms on the tap root ofVicia faba.P. aphanidermatumresulted in a significant reduction in the fresh weight, dry weight and shoot length ofPhaseolus vulgaris. The study shows that several fungal species can be found associated with the roots of beans andVigna unguiculatain Oman and can result in varying disease symptoms. This is the first report of root lesions produced byCurvularia muehlenbeckiaeon the roots ofV. unguiculataand byC. caricae-papayaeonV. radiataworldwide.