5.2.75
BIOLOGICAL CONTROL OF THE POST-HARVEST DISEASES OF COMMON VEGETABLES WITH A NATURAL ANTAGONIST

S PHILIP, RM ZACHRIAH and T RAJKUMAR

College of Agriculture, Kerala Agricultural University, Veilayani 695 522, Kerala, India

Background and objectives
Post-harvest spoilage of vegetables is a serious problem encountered by cultivators and consumers especially in tropical countries. The loss due to microbial spoilage for individual crops is not well documented. Methods aimed at minimising losses after harvest is definitely cheaper than an equivalent increase in vegetable production. The widely accepted practice for the control of post-harvest diseases is the application of fungicides. But this poses several problems. The hazardous impact of agrochemicals used as protective fungicides on vegetables is alarming. The oncogenic risk to consumers is also not fully understood. Hence as an eco-friendly and cost-effective technique, biological methods of plant disease control are gaining momentum. Among the several biocontrol agents available, mycoparasites have attained a significant position in combating post-harvest diseases [1].

Materials and methods
The common vegetables in use, such as tomato (Lycopersicon esculentum), brinjal (Solanum melongena), cucumber (Cucumis melo var. conomon) were selected for the study. Samples with moderate symptoms of rotting were collected from local markets. The pathogenic fungi associated with rotting were isolated and identified. Along with this the epiphytic mycoflora from the healthy samples of the above vegetables were also isolated and identified. This was continued at fortnightly intervals for a period of 3 months.

In vitro studies of the interactions of the epiphytic fungi to the pathogens were made using the dual culture technique [2] and the promising cultures were selected as antagonists. The selected antagonists were tested in vivo by blending and diluting with water at 2% concentration. The vegetables were dipped in this suspension and allowed to dry. After drying they were inoculated with their respective pathogens and stored under room temperature. The effect of the antagonist on the storage quality of vegetables in comparison to the control was studied.

Results and conclusions
Several fungi were found to be associated with the rotting of vegetables. In general the major fungi included Fusarium solani, Rhizoctonia solani, Mucor spp., Colletotrichum gloeosporioides, Alternaria solani, Phytophthora sp. and Pythium aphanidermatum. The damage produced varied from crop to crop and depended upon environmental conditions and the period of storage. The epiphytic flora included a multitude of fungi belonging to all classes.

in vitro studies on the type of interactions by the epiphytic fungi showed over growth, cessation of growth at the line of contact and inhibition. Fungi such as Botryodiplodia theobromae, Phoma sp., Pestalotia palmarum, Trichoderma viride, Aspergillus niger, A. flavus and A. terreus showed antagonisms to pathogens including F. soiani, R. solani and A. solani. T. viride alone was selected for further studies as it was an established antagonist. Inhibition of F. solani by T. viride was effected through coiling and penetration of hyphae, while with R. solani it was through coiling and disintegration of hyphae.

In vivo studies with all the vegetables also revealed the effect of T. viride as a biological antagonist. Vegetables treated with Trichoderma and inoculated with the respective pathogens registered a rotting of less than 50% on the 15th day of inoculation, while in control samples the rotting was 100%. Similarly Trichoderma-treated vegetables (without artificial inoculation by pathogens) retained their freshness and vigour upto 15 days after harvest at a room temperature of 28+2C in contrast to control samples which showed symptoms of rotting.

The study thus indicates the immense possibilities of using Trichoderma formulations as biological antagonists, which can be adapted as an easy and eco-friendly technique for minimising the post-harvest spoilage of vegetables.

References
1. Janisiewiez WJ, 1988. Phytopathology 78, 194-498.
2. Dennis C, Webster J, 1971. Transactions of the British Mycological Society 57, 41-48.