Nematode as a pest of cotton in India
Root Knot nematode, Meloidogyne incognita and Reniform nematode, Rotylenchulus reniformis were identified as important nematode pests of cotton in India. Reniform nematode is distributed in all cotton growing areas and distribution of Root Knot nematode is restricted. Nematode distribution is more in irrigated condition. Apart from causing disease on their own, they do interact with fungi/bacteria to increase the severity of the disease caused by them which in turn resulted in several fold increase in yield loss..Cotton grown under drip has been reported to harbour higher nematode population. In cotton under drip for more than 3 years population of R.reniformis as high as 870 preadults per 250 cc soil recorded (3.48 pre adult/g soil). Fields with high nematode infestation recorded stunting of crop.
Nematode management with fungus
Skimmed milk powder and yeast extract at 1% were found to be the best UV protectant for Lecanicillium lecani which were used in the liquid formulation of L.lecanii. Pseudomonas flourescens isolates, Pf-3,4,6,7 and 8 and Pochonia chlamydosporia were compatible and Pf-4 recorded maximum compatibility of 83.74 per cent. When twenty Pseudomonas flourescens isolates were screened against reniform nematode under in vitro condition 45-100 and 55-100 per cent reduction in hatching and survival was recorded.
Biocontrol consortia with Pseudomonas flourescens and Pochonia chlamydosporia could inhibit the root penetration and number of females/ root , number of egg mass and number of eggs per eggmass of reniform nematode in cotton. The shelf life of this formulation is upto 12 months and no reduction in nematicidal activity was recorded.
Potential fungal endophytes for the management of nematodes in Cotton
A total of 644 entophytic fungal strains were recovered from 2170 tissue segments collected from 434 cotton roots. Of those, 62 per cent of the samples were positive for endophytic fungal colonisation. Root samples were collected from cotton hybrids and varieties, Bt and Non-Bt cotton, G. hirsutum and G. barbadanse. In G. hirsutum, G. barbadanse, Bt, Non-Bt, Variety, and hybrids, the percent endophytic colonisation was 57.89, 67.76, 67.51, 75.68, 72.97, and 75.0, respectively. A total of 71 and 228 endophytic fungal strains were isolated from G. hirsutum and G. barbadanse, respectively, whereas 67 and 577 strains were isolated from Bt and non-Bt cotton. Nineteen fungi were identified as an endophyte in cotton roots. Colonisation frequency of 30.46 per cent was observed for endophytic fungal strains.