STUDIES ON THE INTEGRATED MANAGEMENT OF WHITE ROOT ROT (Dematophora necatrix Hartig) IN APPLE
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Date
2018-10
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UHF, NAUNI
Abstract
ABSTRACT
White root rot of apple caused by Dematophora necatrix Hartig with its perfect stage as Rosellinia necatrix (Prill) is one of the
most prevelant and destructive disease in all the apple growing regions of Himachal Pradesh. It causes serious losses both in nursery as well
as in orchard conditions. Therefore, the present investigation was undertaken with the objectives to study pathogenicity of fungus, host
range, effective concentration that inhibits mycelial growth of the pathogen, compatibility of botanicals, biocontrol agents and fungicides
and their combinations to evolve the effective disease management strategy during the year 2016-2018. The most distinguishing
morphological feature of the pathogen is the presence of a characteristic pear shaped swelling in mycelium at the septa of fungal hypha and
pathogenicity test revealed that symptoms appeared after 13-15 days of pathogen inoculation. In host range studies, fifteen host seeds were
evaluated against D. necatrix both under in vitro and pot conditions. In vitro studies revealed that length of the epicotyl of different host
seeds tested against D. necatrix were less than that of its control. The per cent epicotyl inhibition was found minimum in maize (3.93%)
followed by cauliflower (5.19%) and cabbage (5.65%) seeds. In case of pot experiment, maximum mortality against the test pathogen was
noticed in garlic, fenugreek, soybean, French bean and tomato plants and these plants were killed in 30 days. Root weight of cauliflower,
cabbage and maize seedlings remained unaffected to the inoculation of test pathogen. Thus, the per cent root inhibition was found to be
negligible in cauliflower, cabbage and maize seedlings. Soil pH in different inoculations ranged between 6.1 to 6.9. The host plants cabbage,
maize and cauliflower showed minimum viz. 2.67×104, 2.67×104 and 3.00×104 CFU/g soil as compared to other hosts tested. Therefore
cabbage, maize and cauliflower can be used as an intercrop in apple orchards infested with D. necatrix. Under in vitro studies carbendazim,
(pyraclostrobin + metiram) and (flusilazole + carbendazim) at all the concentrations tested and botanical cabbage (10 %) completely
inhibited the growth of D. necatrix. In compatibility studies, T. viride and T. harzianum were highly compatible with carbendazim,
(pyraclostrobin + metiram), (flusilazole + carbendazim), cabbage + carbendazim, cabbage + (pyraclostrobin + metiram), cabbage +
(flusilazole + carbendazim). They showed negligible diametric growth of D. necatrix and 100 per cent mean mycelial growth inhibition,
while, they were least compatible with cabbage showing 7.48 mm and 7.89 diametric growth with 56.07 and 53.99 per cent mean mycelial
growth inhibition, respectively. Under pot culture conditions, the combinations viz. T. viride + carbendazim , T. viride + (pyraclostrobin +
metiram), T. viride + (flusilazole + carbendazim), cabbage + carbendazim , cabbage+ (pyraclostrobin + metiram), cabbage + (flusilazole +
carbendazim), T. viride + cabbage + carbendazim, T. viride + cabbage + (pyraclostrobin + metiram), T. viride + cabbage + (flusilazole +
carbendazim), T. harzianum + carbendazim , T. harzianum + (pyraclostrobin + metiram), T. harzianum + (flusilazole + carbendazim), T.
harzianum + cabbage + carbendazim, T. harzianum + cabbage + (pyraclostrobin + metiram), T. harzianum + cabbage + (flusilazole +
carbendazim), carbendazim , pyraclostrobin + metiram and flusilazole + carbendazim were highly effective and provided complete control
of the disease when applied twice at 7 days interval after soil inoculation with the test pathogen. The root weight of above treatments ranged
between 24.47g to 29.07g, which were found higher than that of control (18.83g). The pH of the soil of all treatments ranged between 7.0 to
7.5 while the total microbial count of treated plants lied between 10.67 to 14.33×104 CFU/ g soil which were more than that of control plant.
The combined application of biocontrol agents, botanical and fungicides control the disease more effectively as compared to their individual
treatment.
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