EXPLOITATION OF PLANT GROWTH PROMOTING RHIZOBACTERIA FOR THE MANAGEMENT OF STEM AND POD ROT OF GROUNDNUT CAUSED BY Sclerotium rolfsii Sacc.
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Date
2018-07-30
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UNIVERSITY OF AGRICULTURAL SCIENCES, RAICHUR
Abstract
Sclerotium rolfsii causing stem and pod rot of groundnut is a potential threat to
groundnut production. During survey, mean stem and pod rot incidence was maximum in
Ballari district (31.5 % and 29.39 % respectively) and least incidence (12.78 % and 3.04
%) was in Bagalkot district. A total of nineteen isolates of each of the rhizobacteria were
screened against S. rolfsii in vitro. Maximum mycelial inhibition of S. rolfsii was
recorded by PF-2 (75.18 %), BS-3 (58.51 %) and S-2 (56.66 %) and least inhibition was
recorded in PF-13 (2.59 %), BS-14 (1.48 %) and S-17 (2.2 %) (Pseudomonas fluorescens,
Bacillus subtilis and Streptomyces spp. respectively). Five superior isolates of P.
fluorescens produced fluorescens under UV light, yellowish green pigmentation, rod
shaped cells. The B. subtilis isolates were rod shaped and colony was rough. The colony
colour was white in BS-6 and creamy in rest of the isolates. The S-3 isolate of
Streptomyces spp. was creamy, S-6 was light grey and rest three were white in color. All
the isolates produced rough colonies, showed yellow pigmentation when the plates held
in reverse condition and the S-3 produced brown colored pigmentation. All the isolates of
P. fluorescens showed gram negative reaction, positive for KOH test, catalase test, starch
hydrolysis, urease test, casein hydrolysis, gelatin liquefaction, indole and H2S test.
Whereas, B. subtilis and Streptomyces spp. isolates showed positive for all the tests
except for KOH and indole test. All the tested isolates of each of the rhizobacteria
produced HCN, siderophore, IAA and volatile compounds. The shelf life of PF-2, BS-2
and S-3 was maximum in talc (1.9, 1.8 and 1.4 x108 cfu/g respectively) and least was in
rice bran (1.2, 1.1 and 1.0 x108 cfu/g respectively) up to 150 days. In pot culture
management of stem and pod rot, chemical fungicide carbendazim 25 % + mancozeb 50
% showed very less incidence (20.00 % and 14.50 % respectively) and highest disease
was noticed in pathogen alone treated seedlings (80.00 % and 66.33 %).
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