Identity and Toxicity of FUsarium Species Isolated from Wilted Chickpea

Abstract

Four cultures of fungi, identified as Fusarium oxysporum f. sp. ciceris, were received from the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India. The cultures were race 1, a race designated as V2, race 2, and an isolate from Jabalpur which, on geographical evidence, was probably race 4, the races being defined on the basis of the reaction to them of a set of differential cultivars of the host. A further isolate, also identified as Fusarium oxysporum f. sp. ciceris, but of unknown race was received from the Thal region of Pakistan. Culture filtrates of all the isolates, grown on a defined medium, were toxic to cells of chickpea leaflets, separated enzymatically from the plant, but filtrates of the Thal isolate were the most toxic. Isolate toxicity was affected by incubation temperature and time, the maximum toxicity for the Thal isolate being 72 units activity ml-1 cultural filtrate when it was grown at 20ºC for 12 days but only 7 units activity ml-1 when grown at 30ºC for the same period. When ribosomal DNA sequences of the four ICRISAT isolates were compared, those of race 1 and V2 were identical for all 392 bps, suggesting that V2 is a variant of race 1. The Jabalpur isolate was a 99% (390/392 bps) match with race 1 and V2 and race 2 was a 97% (391/400 bps) match with race 1 and V2. Although the Thal isolate gave a 99% match with the race 1 and V2 for the first 262 bps (one gap) and a 89% match (59/66 bps) for bps 338–403, there was considerable divergence in the region from 263 to 337 bps. Similar results were obtained when the Thal isolate was matched with race 2 and 4. The four ICRISAT isolates were confirmed as Fusarium oxysporum but various formae speciales in the GenBank database such as vasinfectum and vanillae were equally well matched. No sequence for F. oxysporum f. sp. ciceris was present in the GenBank database. In contrast, the Thal isolate gave an almost exact match with Fusarium acutatum (407/408 bps) and the morphology of the Thal isolate, when viewed under the microscope, accorded well with the description of F. acutatum given in the literature.