Department of Botany, University of Rajasthan, Jaipur, India

Background and objectives
Heterodera cajani is a serious nematode pest of Vigna unguiculata. The fungus Verticillium chlamydosporium has attained a considerable reputation as a potent biological agent for the control of cyst nematode [1].The present study was therefore conducted so as to find out the efficacy of V. chlamydosporiumagainst H. cajani, to screen the suitable substrate for its mass culture and to determine the optimum dose of the fungus-infested substrate so as to manage the nematode in a more economical way.

Materials and methods
Overall, three experiments were conducted. In the first experiment the efficiency of V. chlamydosporium was tested in vitro. The fungus was cultured on liquid potato dextrose medium and fungal filterate was obtained by removing the 15-day-old mycelial mat and filtering the media through Whatman paper no. 1. Different dilutions were then prepared adding required amount of sterilized water. Five freshly collected equal sized cysts with egg masses were transfered to each petri plate containing 5 ml of different dilutions of the culture filterate. The number of hatched juveniles were counted after 48 and 72 h. Seventeen substrates were screened for the growth of V. chlamydosporium under aseptic conditions. Twelve days after, the flasks were taken out the spore load per gram of substrate was calculated. In another experiment, fungal treatment was given to the soil at three different dosages, 4, 8 and 12 g. Nematization was done a week after fungus inoculation by 1000 larvae/kg soil. Observations were taken 90 days after treatment.

Results and conclusions
Observation taken indicated that the culture filterate of V. chlamydosporium is effective in inhibiting the larval hatch of Heterodera cajani. It was noted that the larval emergence was inversely proportional to the filtrate concentration and duration of exposure. Total inhibition of larval hatch was observed at 5 ml concentration where no hatching was observed upto 48 h. Gradual increase in egg hatching was then recorded with decrease in the concentration of the culture filtrate and increase in the time of exposure. Thus it could be inferred from the present investigation that fungus taken in the trial is capable of producing certain toxic substances that inhibits the larval emergence of the H. cajani eggs, and the presence of such fungi in the rhizosphere could be of great help in dealing with the deleterious nematodes and suppressing their rising population.

Seventeen substrates including grains, straws, dungs wheat bran and added to mass culture the experimental fungus revealed that best results were evident on rice followed by wheat and wheat bran. As grains are not economically feasible the cheaper substrate wheat bran was used for the mass multiplication of the fungus. Application of decomposable organic matter to the soil so as to inhibit the plant parasitic nematodes is a well known practice. Thus in addition to the deleterious effect of wheat bran on nematodes it also supplied food to the nematophagous fungus growing in vicinity of the roots. Enhancement in the plant growth characters were found with application of fungus to the soil. The dose of 4 g/kg soil of the nematophagous fungus comprised wheat bran though helped in overcoming the ill-effect of the nematode by slightly aggravating the plant growth, better results were obtained by increasing the fungal dose to 8 and 12 g/kg soil. Reduction in cyst number and cyst content was also directly proportional to the concentration of the nematophagous fungus used. Comparable results obtained at the dose of 8 and 12 g led to the conclusion that 8 g/kg soil of fungus infested wheat bran may be considered as an optimum dose to check H. cajani populations.

1. Kerry BR, 1981. Biological control in crop production. Symposium Allanheld, Osmurn, Totawa, pp. 79-90.