Co-infection of Tylosema esculentum (Marama bean) seed pods by Alternaria tenuissima and a Phoma spp.

Abstract

Marama bean, Tylosema esculentum, is an endemic, perennial wild tuberous Fabaceae, widely distributed in the Southern Kalahari (Namibia, Botswana and to a lesser extends in South Africa). It is well adapted to the deep sandy soils of the Kalahari. It is drought avoiding. It has been valued by the indigenous people of the semi arid land of the Kalahari for its nutritional and medicinal qualities. The aim of the study was to determine the identity of fungal pathogens that occur on marama bean. Diseased pods presenting necrotic spots with dense sporulation in the centre were collected. They were subjected to fungal isolation using potato dextrose agar (PDA) at room temperature under fluorescent light for five days. Two fungi with different cultural conidial morphology were isolated. Single spores from the two cultures were separately inoculated on PDA to obtain a pure culture. Genomic fungal DNA was extracted from fresh mycelium using the cetyl trimethylammonium bromide (CTAB) method and was used as a template in internal transcribed spacer (ITS) PCR amplification. Based on the sequence analysis of the 5.8S ribosomal DNA and the ITS, the two isolates associated with necrotic Marama pods were identified as Alternaria tenuissima and Phoma spp. Isolate Po72 due to the high sequence homology, which was 99% in both cases. To our knowledge, this is the first report describing the presence of these two fungi on Marama bean.

Key words: Marama, ITS, fungal pathogen, Tylosema esculentum.