M.Sc. (Agri.) dissertation
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Date
2005
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Publisher
AAU, Anand
Abstract
Investigations on various media for establishing their suitability for
favourable growth and efficacy of agrochemicals and bio-pesticides including
phytoextracts for their inhibitory action against Cercospora nicotianae, the cause of frogeye
spot disease of bidi tobacco under in vitro conditions were carried out at Bidi
Tobacco Research Station, Anand Agricultural University, Anand during 2003-04. In
subsequent study, effective fungicides, insecticides, readymade bio-pesticides and
acqueous leaf extracts of plant species were tested against the disease under nursery
conditions. Reaction of bidi tobacco varieties/genotypes against the disease under nursery
conditions was also studied
Out of 7 media evaluated, carrot leaf decoction agar, fennel leaf decoction
agar, coriander leaf decoction agar and sava leaf decoction agar were found to be highly
favourable for good growth of C. nicotianae (52.40 to 60.80 mm colony diameter).
Among these, fennel leaf decoction agar, coriander leaf decoction agar and sava leaf
decoction agar were established for the first time as suitable media for the growth of the
fungus (52.40 to 54.80 mm colony diameter) under laboratory condition.
Carbendazim, thiophanate methyl, benomyl, mancozeb and Cosco
(Carboxin 37.5 % + Thirum 37.5 %) 75 WP were most effective and completely
suppressed the growth of the fungus on carrot leaf decoction agar under in vitro
condition. Out of 16 insecticides, carbaryl and dichlorovos were effective and inhibitated
the growth to the extent of 85.9 and 82.6 %, respectively.
Among 29 plant species evaluated, acqueous leaf extract of Tecoma stans
@ 25 % was most effective (76.0 % inhibition); this was followed by E. citriodora
(49.0 % inhibition). Six readymade bio-pesticides viz., Econeem, Biosoft, Halt,
Vanguard, Monitor-WP and Biolep were found highly effective in inhibiting the growth
of C. nicotianae in vitro; the per cent inhibition ranged between 75.3 and 92.4.
Results of evaluation of effective fungicides, viz., carbendazim @ 0.025 %,
thiophanate methyl @ 0.07 %, mancozeb @ 0.2 %, Cosco @ 0.3 % and benomyl @
0.025 %, leaf extracts of plant species viz., Tecoma stans and Eucalyptus citriodora, both
at 25 %, insecticides carbaryl @ 0.2 % and dichlorovos @ 0.05 % and readymade biopesticides
viz., Econeem @ 0.075 % and Biosoft @ 0.4 % under nursery conditions
revealed that among fungicides, carbendazim and thiophanate methyl were most effective
in the management of the disease giving better yield of transplants; these fungicides gave
100 and 96.6 % control, respectively. Between two plant species, acqueous leaf extract of
T. stans gave 85.0 % control of the disease and significantly more number of transplants
than control. Taking into account two most important attributes in the nursery viz., per
cent disease intensity and transplants, two insecticides and two readymade bio-pesticides
tested were not considered as effective against the disease.
Among 10 different varieties/genotypes screened none was found free from
the disease under nursery conditions. The variety GTH1, however, had minimum per cent
disease intensity (45.60) and the variety Anand 119 had maximum per cent disease
intensity (73.67).
The results of the present investigations, thus, indicated that in addition to
carrot leaf decoction agar, three more media viz., fennel leaf decoction agar, coriander
leaf decoction agar and sava leaf decoction agar were established as favourable for the
growth of C. nicotianae under laboratory condition. Two fungicides, carbendazim and
thiophanate methyl, were most effective in the management of the disease in nursery.
Efficacy of acqueous leaf extract of T. stans against frog-eye spot disease in nursery was
established for the first time; it was found to yield significantly more number of
transplants when compared with control. Leaf extract of T. stans could be used
individually as botanical pesticide in minimizing losses due to the disease in question or
it could be integrated with chemical fungicide/s. If integrated, it could help in minimizing
frequency of applications of chemical fungicide/s, thus reducing the cost of seedlings
production. Under these circumstances, it would also minimize the danger of resistance
development in C. nicotianae under nursery conditions. However, detailed integrated
schedule would need to be worked out before it can be advocated to the growers.
Since none of the ten varieties/genotypes of bidi tobacco was resistant, it
ultimately suggested that more extensive work involving very large number of genotypes
is needed in order to locate resistance or tolerance to frog-eye spot disease.
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Keywords
agriculture, plant pathology, study