Diversity of Fusarium Isolates Causing Wilt of Hot Pepper in India.

India is a major producer, consumer and exporter of hot pepper with an area of 883,000 ha having a productivity of 1,266 kg ha-1. Fusarial wilt is one of the most serious problems in some of the major hot pepper growing states in black cotton soil. Yield losses due to Fusarium wilt may be as high as 25 percent. One hundred and forty nine isolates of Fusarium of chilli from ten different states were characterized for morphological, cultural, pathogenic and molecular properties. Significant variation existed among the isolates regarding rate and type of growth, mycelial width, sporulation, and number and pattern of chlamydospore formation. Fifty two isolates of F. solani were fast growers, 36 isolates possessed larger macroconidia (>20µm), 123 isolates were having 1-3 septa, 52 isolates were abundantly sporulating whereas another 53 isolates were poor sporulators. Based on the reaction of these isolates on differential hosts, two races/pathogenic variants were identified. The highly virulent races were from Tamil Nadu, Maharashtra, Andhra Pradesh, Rajasthan and Gujrat whereas moderately virulent races were prevalent in Karnataka, Orissa and New Delhi. Of the 35 primers surveyed, 5 of them, namely OPA 2, 8, 12, 18 and OPC 11 showed distinct polymorphism. The RAPD-PCR analysis indicated two clusters, groups A and B. Group A consisted of only two isolates (F63 and F97 from Tamil Nadu and Gujarat respectively). Group (B) comprised of 43 isolates which were divided into 2 sub-groups comprising 2 isolates in one sub-group and 41 isolates in another sub-group sharing the same genetic similarity coefficient. Interestingly, the cluster A comprising F63 and F97 isolates which were in an entirely different molecular group, belonged to highly virulent variant, as determined in pathogenic variability. This highly virulent variant differed at the molecular level showing high divergence from the remaining isolates.