Race profiling, genetic diversity, diagnostics and management of Fusarium oxysporum f. sp. ciceris causing wilt in chickpea

Abstract

Fusarium oxysporum f. sp. ciceris (Foc) is a soil and seed- borne fungal pathogen causing chickpea wilt worldwide and produces typical vascular wilt symptoms in India. The populations were highly variable in their growth pattern and rate, size of macroconida and pigmentation in culture. The studies clearly indicate the need to revise the International differential cultivars standardized in 1982 for characterization of the Indian populations of Foc into races. A set of new differential cultivars namely, C104, JG74, CPS1, BG212, WR315, KWR108, GPF2, DCP92-3, Chaffa and JG62 was identified and based on differential reactions; the Indian populations of Foc were characterized into eight races. Genetic diversity analysis using various molecular markers such as RAPD, URP, ISSR and SSR indicated the existence of variability among the populations predominated by a single race of the pathogen in an area. The groups partially corresponded to the states of origin/chickpea-growing region of the isolates as well as races of the pathogen. Gene specific markers such as TEF-1a, b-tubulin, and ITS were also used to determine the genetic diversity and about 90% populations showed more or less similar grouping pattern with these markers. The groups did not correspond to the state of origin and races of the pathogen. High level of similarity among the populations in respect of these gene sequences was observed. Highly sensitive and specific molecular markers from various genomic regions as well as SCAR markers were developed for detection of the pathogen using both conventional and real-time PCR. For management of the disease, efficacy of various bio-agents was evaluated and Trichoderma harzianum and T. viride were found effective. Novel seed dressing and soil application formulations were developed from these bio-agents. A combination of PBP 4G (T. viride) for soil application and Pusa 5SD (T. harzianum) for seed treatment together with a fungicide, carboxin provided the highest seed germination, shoot and root lengths and grain yield with the lowest incidence of wilt in chickpea under field conditions. The efficacy of seed treatment with Pusa 5SD has been validated at different locations in India. Further, a combination of seeds treated with Pusa 5SD developed from T. harzianum + Pseudomonas fluorescens 80 + Mesorhizobium ciceri + Vitavax power also provided the highest germination, grain yield and the lowest wilt incidence.