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BIOLOGICAL CONTROL OF ROOT ROT OF CLUSTER BEAN (Cyamopsis tetragonoloba L. Taub.).

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Title BIOLOGICAL CONTROL OF ROOT ROT OF CLUSTER BEAN (Cyamopsis tetragonoloba L. Taub.).
 
Creator MUSAED NAJI EISSA NASSER
 
Contributor PRAMOD CHANDRA KUMAR, C
 
Subject BIOLOGICAL, CONTROL, ROOT, ROT, CLUSTER, BEAN
 
Description Cluster bean or guar (Cyamopsis tetragonoloba L. Taub.) is an economically
important vegetable crop. It is consumed as vegetable in India. Gum extracted from
seeds has a varied range of industrial applications. Cluster bean cultivation is gaining
importance in and around Hyderabad and Andhra Pradesh in view of its commercial
value. In recent years the crop yield are declining due to biotic and abiotic stresses. Of
the biotic stresses, the diseases caused by fungi, bacteria and viruses are of economic
importance. Among the fungal diseases, root rot disease caused by Sclerotium rolfsii
Sacc. has become the constraint resulting in yield losses year after year . A detailed
study was carried out on the biological control of this disease by analysing
quantitative and qualitative rhizosphere microflora, in vitro screening of native
rhizosphere microflora, exotic and commercial formulations of fungal and bacterial
biocontrol agents, compatibility of potential antagonists with commonly used
fungicides. The studies also included testing of the potential antagonists and
compatible fungicides either applied alone or in combination against test pathogen
under glasshouse conditions.
The disease symptoms were initially characterized at seedling stage. Thirty
days old plants showed root rot symptoms in warm conditions. The wilted plants
showed gradually or sometimes sudden yellowing, withering and drying of leaves
followed by drying of entire plant. The wilted plants showed light brown
discolouration on the plant tip and whitish mycelial growth on the collar region and
root due to the blocking of xylem and phloem. Wilting of the plant with dropping of
the leaves occured when 30-32◦ C temperature prevailed during daytime. The infected
plants usually wilted within 3 to 5 days, after the appearance the first root rot
symptoms. The fungus associated with the disease was isolated and identified as
Sclerotium rolfsii Sacc. and its pathogenicity was proved under glasshouse
conditions.
Nine fungi were isolated consistently from the rhizosphere of cluster bean
(cv. Pusa Navbahar) plants at 15 DAP, 30DAP and 45 DAP stages by serial dilution
method. Of these, Penicillium citrinum was found to be the predominant in the
rhizosphere of cluster bean (cv. Pusa Navbahar) compared to Emericella sp with least
per cent occurrence. Quantitative analysis of rhizosphere microflora of cluster bean
revealed that the population of fungi and bacteria gradually increased from 15 DAP
(seedling) to 30 DAP (vegetative) to 45 DAP (flowering) stages.
In vitro screening of cluster bean rhizosphere microflora against S. rolfsii
resu1ted in identifying potential native antagonists like Trichoderma viride (Native 1
Tv) followed by Trichoderma viride (Native 2 Tv). Among the native, exotic and
commercial biocontrol agents, T. viride (Native 1 Tv), T. harzianum (DOR Th) and
B. subtilis (DOR Bs) were found to be the best among all the isolates tested in
inhibiting the growth of test pathogen. The non Trichoderma groups of fungi were
less effective in inhibiting the pathogen growth.
In compatibility studies, T. viride (Native 1 Tv), T. harzianum (DOR Th)
and B. subtilis (DOR Bs) were found to be compatible with azoxystrobin at its
recommended and half recommended dosages.
The efficacy of potential antagonists and compatible fungicide either alone
or combination as a seed or soil application were tested in pot culture against the test
pathogen wherein the treatment T14 involving combined seed treatment/soil
application of B. subtilis (DOR Bs) and azoxystrobin (0.1%) was found to be superior
by recording significantly in highest per cent germination of cluster bean (cv. Pusa
Navbahar) seedlings and least per cent disease incidence (15.08) compared to other
treatments.
 
Date 2016-08-08T14:17:46Z
2016-08-08T14:17:46Z
2008
 
Type Thesis
 
Identifier http://krishikosh.egranth.ac.in/handle/1/71541
 
Language en
 
Relation D8173;
 
Format application/pdf
 
Publisher ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD