ETIOLOGY, EPIDEMIOLOGY AND MANAGEMENT OF WILT OF POMEGRANATE CAUSED BY Ceratocystis fimbriata Ellis and Halst.
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Date
2017-09
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UNIVERSITY OF HORTICULTURAL SCIENCES, BAGALKOT
Abstract
A survey was carried out in major pomegranate growing districts of
Karnataka to know the incidence of wilt during 2015-16, which revealed that the
highest incidence of disease in Bagalkot district (15.27 %) and least in Chirtradurga
district (3.75 %). Four years and above old orchards under black soil showed a higher
incidence of wilt, shot hole borer and root knot nematode infection. Among the soil
parameters electric conductivity of soil showed the significant positive correlation
with per cent disease incidence. Among the ten media tested, all the five isolates
showed the maximum growth and sporulation on oat meal agar, potato dextrose agar,
malt extract agar. The temperature of 25°C, pH 5.0 and light alternates with 12 hr. of
darkness were found best for the growth and sporulation of C. fimbriata. Starch and
potassium nitrate were found to be the best carbon and nitrogen sources for the
growth of the fungus, respectively. The soil inoculum level of 12 per cent
concentration of C. fimbriata found to cause 98.33 per cent disease incidence.
Survivability studies revealed that C. fimbriata can survive up to 34 weeks under
refrigerated condition while it was 22 weeks in laboratory and 28 weeks in field
condition. Soil temperature of 250C showed the maximum per cent colonization of the
fungus on carrot baits. The cent per cent disease incidence was recorded at moisture
level of 50, 60 and 70 per cent. The AUDPC and apparent rate of infection ‘r’ value
was 142.50 and 0.13 at the end of September month respectively. Multiple regression
analysis revealed that weather parameters influence to the extent of 44.00 per cent on
per cent disease incidence. Step wise multiple regression analysis showed that among
the weather parameters maximum variation was explained by rainfall (30.66 %).
Twenty isolates of C. fimbriata were amplified at 500 bp length and isolates were
sequenced and deposited in the GenBank under the accession numbers from
KY987496 to KY987515. All isolates from different districts of Karnataka showed
specific pattern of similarity according to geographical region. Among non-systemic
fungicides cymoxanil + mancozeb, mancozeb and captan completely inhibited the
mycelia growth of the fungus at all the concentrations tested. All the systemic
fungicides tested showed 100 per cent inhibition except azoxystrobin. Among the
bioagents Trichoderma harzianum-55 showed strong antagonistic activity against
C. fimbriata. In the field experiment propiconazole (0.2%), propiconazole +
difenoconazole (0.2%), tricyclazole (0.2%) and tebuconazole (0.2%), drenching four
times at 15 days interval showed the maximum disease control with higher fruit yield
and net returns.
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