STUDIES ON CASTOR (Ricinus communis L.) WILT CAUSED BY Fusarium oxysporum f. sp. ricini Nanda and Prasad
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Date
2020-10-01
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University of Agricultural Sciences, Bangalore
Abstract
Castor wilt caused by Fusarium oxysporum f. sp. ricini is a potential threat for
commercial cultivation of crop. The fungus isolated from roots of wilted castor plants on
PDA produced fluffy mycelia with purple pigmentation. Pathogenicity was established by
proving Koch’s postulates. Based on pathogenicity and morphological characters the
pathogen was identified as F. oxysporum f. sp. ricini by comparing with the original
descriptions. Cultural studies revealed that highest growth on different media viz.,
Sabourauds dextrose agar, carrot agar and Richard’s synthetic agar. But profuse sporulation
was in rose Bengal agar, host leaf extract and PDA. The fungus grew well at temperature
of 25°C with highest dry mycelial weight of 373.3 mg with abundant sporulation at 25°C
and 30°C whereas slightly acidic pH (5-6) favoured good growth and sporulation. Among
the fungal bioagents Th14 strain of Trichoderma harzianum exhibited maximum inhibition
and Bacillus velezensis (P42) showed highest inhibition among the bacterial bioagents.
Among the fungicides tested in vitro, combi products viz., carbendazim + mancozeb,
tebuconazole + trifloxystrobin and azoxystrobin + difenoconazole showed complete
inhibition at 150, 250, 500 ppm; contact fungicide mancozeb at 1000 ppm; systemic
fungicide carbendazim at 150 ppm were found to be superior in inhibiting growth. Out of
39 entries screened under glasshouse condition, six genotypes viz., Konehalli, ICS-252,
BCH-43, BCH-89, BCH-95, 48-1 were found highly resistant.