Studies on cultural and morphological variability of Fusarium spp. and Rhizoctonia solani causing wilt and root rot complex of chickpea

Abstract

Fusarium oxysporum f.sp. ciceri (one isolate), Fusarium solani (five isolates) and Rhizoctonia solani (six isolates) were isolated and their pathogenicity were confirmed by growing chickpea in pathogen inoculated soil. The isolates of F. solani and R. solani exhibited considerable variations in growth, colony character, spore and sclerotial size. The five isolates of F. solani showed variations in radial growth and in spore morphology. The size of macro conidia ranged from 8.8 × 2.5 µm of isolate UDP Rs-1 to 10.5 × 2.7 µm of SRH Rs- 5 and micro conidial size ranged from 3.2× 1.2 µm to 5.1× 1.0 µm This showed that variability in Fusarium spp. exists only with respect to cultural characters. Chlamydospores of Fusarium oxysporum f.sp. ciceri measured 4.3-6.6 µm in size. The five isolates of F. solani did not show much variation in chlamydospores size, and these ranged from 4.7-6.5 µm to 5.6-7.2 µm. All the six isolates of R. solani differed in colony characters and showed black colored cultures with 90.0 mm colony diameter on 7th day of incubation under uniform environments and medium. Sclerotial formation was recorded in all the six isolates of R. solani. Morphology of sclerotia varied from 1.0 × 0.8 mm of UDP Rs-1 and 1.8 × 1.3 mm of TIB Rs-3. The results showed variations in growth and sclerotial formation among R. solani isolates. In vitro studies were conducted to determine the optimum range of temperatures for mycelial growth and sporulation of the isolates of F. solani, Fusarium oxysporum f.sp. ciceri and R. solani. The results obtained in the present study indicates that out of the five temperatures viz., 15, 20, 25, 30 and 35â°C, the maximum mycelial growth and sporulation of the isolate of Fusarium oxysporum f.sp. ciceri were recorded at 30â°C and the minimum at 15â°C temperature. Also, all the five isolates of F. solani showed the maximum mycelial growth and sporulation at 30â°C and the minimum growth and sporulation were recorded at 15â°C, the six isolates of R. solani showed the maximum mycelial growth at 30â°C and the highest sclerotial formation at 35â°C and the minimum at 15â°C temperature. Fungi can grow over a wide range of pH but optimum for mycelial growth may differ for each species or even within species. The relationship of pH to the mycelial growth and sporulation of Fusarium spp. and sclerotial formation of R. solani was determined in vitro at different pH levels viz., 4.0 to 8.0 at 20â°C. The present studies revealed that Fusarium spp. and R. solani grew at wide range of pH (6-8). The maximum growth and sporulation of the isolate of Fusarium oxysporum f.sp. ciceri was observed at pH 7 while the minimum at pH 4. The five isolates of F. solani showed the maximum growth and sporulation at pH 7 and the minimum at pH 4. The isolates of R. solani showed the maximum growth and sclerotial formation at pH 7 and the minimum at pH 4.