ISOLATION AND CHARACTERIZATION OF ENTOMOPATHOGENIC ...

Out of nine insecticides, endosulfan, quinolphos, monocrotophos, chlorpyriphos, oxydimeton
methyl, dichlorvas, dicofol, malathion and dimethoate were included to know their effect on V. lecanii
in vitro. Irrespective of concentration, there was 37.31 to 69.18 per cent inhibition of conidial
germination (Table 21). Among them, malathion was significantly detrimental (69.18% inhibition) than
all other insecticides except quinolphos (66.76%). Conversely, endosulfon and chlorpyriphos were
signficinatly safer (37.31 to 44.37%), followed by oxydemeton methyl and dimethoate (45.33 to
48.27% inhibition).
4.6.3 Weedicides
All the weedicides evaluated for their interaction with M. anisopliae in general, inhibited the
germination of the fungal conidia to the extent of 9.01, 16.09, 26.61 and 41.95 per cent at low,
medium recommended and high dosages, respectively (Table 22). However, the effect of all the
weedicides on conidial germination of the mycopathogen was equal irrespective of the concentration
tested. The inhibition ranged from 2.01 to 15.16, 9.80 to 22.41, 15.60 to 34.43 and 29.10 to 59.46 per
cent at low, medium, recommended and higher concentration, respectively.
Weedicides, in general, inhibited the germination of the fungus V. lecanii to the extent of 8.65,
17.46, 25.85 and 36.12 per cent of low (one fourth and half the recommended), recommended and
high (double the recommended) dosage respectively. Variation between the concentration was
evident (Table 23). However, the effect of all the weedicides on conidial germination of the
mycopathogen was equal irrespective of the concentration tested which ranged from 0.73 to 13.07,
7.53 to 22.28, 15.51 to 34.42 and 24.30 to 48.06 per cent at low, recommended and high
concentration, respectively.
4.7 PERSISTENCE OF M. anisopliae (Ma2) AND V. lecanii (Vl1) ON
PHYLLOPLANE AND SOIL
The persistence of M. anisopliae Ma2 and V. lecanii Vl1 were evaluated on the phylloplane
and soil of cotton under in vitro condition. The results are presented in Table 24 and 25.
4.7.1 In soil and phylloplane
Persistence studies of M. anisopliae and V. lecanii on soil and phylloplane were carried out in
field and simulated field conditions over a period of 16 months. Immediately, after inoculation of M.
anisopliae into soil, colony forming units (cfu) ranged from 25.6 x 10 9 to 35.2 x 10 5 per g of soil in field
and simulated field conditions respectively. In the subsequent observations made at monthly interval,
colony counts dropped gradually as the time lag increased (Table 24). The persistence of conidia was
more under simulated field conditions i.e. upto 16 months with 2 x 10 4 cfu per g of soil whereas under
field conditions it persisted only till 5 months. In simulated field condition, slight increase in cfu was
encountered and continued upto declining phase.
Phylloplane treated with aqueous suspension @ 4 x 10 6 conidia indicated that persistence in
field condition and simulated field condition decreased from 1.31 x 10 2 and 1.04 x 10 2 cfu on the initial
day of spray to 0.05 x 10 2 and 0.19 x 10 2 after two months.
Initially under simulated field condition, the colony forming units (cfu) of V. lecanii accounted
for 32.3 x 10 5 in soil and 1.47 x 10 2 on phylloplane. In the subsequent observations after every month,
the colony counts dropped gradually to 2 x 10 4 after 360 days of inoculation in soil, whereas on
phylloplane the mycopathogen, persisted upto 120 day of exposure with 0.02 x 10 2 cfu.
Persistence studies of V. lecanii under field conditions revealed that the mycopathogen
persisted, only for a period of three and two months in soil and phylloplane respectively (Table 25).
The colony counts dropped from 20.3 x 10 9 and 1.29 x 10 2 to 0.2 x 10 2 and 0.14 x 10 2 in soil and
phylloplane respectively.