Variability in isolates of Fusarium. oxysporumf. sp. ricini, castor wilt pathogen.

Abstract

Castor is an industrially important non-edible oilseed crop grown in arid and semi arid regions and India is the world’s largest producer of castor seed. Wilt (Fusarium oxysporum f. sp. ricini, Nanda and Prasad) is the most important soil and seed borne disease of castor. Monocropping followed due to its high economic return resulted in the endemic development of wilt which became the limiting factor in castor cultivation in India. Pathogenic variability and aggressiveness in the pathogen is the main cause of breakdown of resistance in host cultivars. The differential reaction of varieties and breeding lines over the years and across the locations indicated prevalence of variants in the pathogen. Pathogenic variability of 75 F. oxysporum f. sp. ricini (For) isolates was tested on castor cultivars viz., Kranthi, JI 35, Haritha, VP-1, 48-1, JI 258 and DCS 9 under pot culture conditions by sick soil method and wilt incidence was recorded at intervals. Many isolates showed 100% wilting with JI-35 while low wilt was recorded with 48-1, JI-258. In Kranthi and VP-1 wilt incidence was more with most of the isolates. 13 Fusarium isolates viz., no.53 (Narkhoda), 59 (Nandimalla gadda) , For- 12-1, 2, 3 (Palem), 10 (Yethapur), 13- 19, 20 (Anand) ,For- 12-16 (Hiriyur, KA), For- 13-33 (Junagadh, GJ), For-180 (Palem), For-113 (Narkhoda),For-112 (Narkhoda) were highly virulent (> 75% wilt incidence ) in tested cultivars. The isolates For-12-13, For-12-11, For- 13-38, For- 13-39 were less virulent and showed low wilt incidence. Apart from castor cultivars, Tapoica and Jatropa which are closely related to castor also were artificially inoculated with wilt pathogen for developing differential lines and were found to be non hosts for F. oxysporum f.sp. ricini.