Thick succulent leaves of Malabar spinach (Basella alba L.) are used for human consumption in India. Symptoms of leaf blight were observed on this plant in October 2010 at Umiam, Meghalaya, India. Symptoms started from the lower leaves and spread to the upper part. Water-soaked lesions covered the whole leaf and gradually the leaves shredded and got detached from the plants. Whole plants were seen defoliated due to severe infection. Lesions were visible on the stem also. The pathogen was isolated on potato dextrose agar amended with streptomycin (100 ppm). Fungus isolated from infected plants had typical characters associated with Rhizoctonia solani J. G. Kühn [teleomorph Thanatephorus cucumeris (A.B. Frank) Donk], i.e., hyphal ramification angles of ~90°, basal constriction, and a septum next to the lateral hyphae (2). Nuclear staining with DAPI (2-(4-amidinophenyl)-1H-indole-6-carboxamidine) confirmed that hyphal cells were multinucleate (1). Molecular analysis was conducted using sequence data (JQ675535) containing ITS1 and 5.8S and ITS 2 of nrDNA, which was obtained after amplification using universal primers ITS1 and 4. BLAST search revealed 99 to 100% similarity with AG 1-IB (GU585667, GU270581). Living culture has been deposited in Agharkar Research Institute, Pune, India (NFCCI No. 2601). Phylogenetic analysis was also conducted using MEGA 5. It also placed the isolate in AG 1-IB clade with 99% bootstrap support in MP (maximum parsimony) analysis. Three healthy plants were inoculated using colonized PDA bits from actively growing culture. Sterilized PDA bits were kept on control plants. Plants were sprayed with water and covered with cheesecloth for 3 days. Inoculated plants developed symptoms after 5 days whereas control plants remained healthy. Inoculations were also done on detached leaves kept in a moisture chamber using colonized PDA bits. In this case, symptoms developed within 3 days. Detached leaves with sterilized PDA bits remained healthy. R. solani was also reisolated from inoculated plants. To our knowledge, this is the first record of AG 1-IB based on molecular evidence on B. alba from India. This new host may accelerate the spread of this pathogen to other crops.
References: (1) M. M. Kulik and P. D. Dery. Biotech. Histochem. 70:95, 1995. (2) B. Sneh et al. Identification of Rhizoctonia species. APS Press, St Paul, MN, 1991.