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INTEGRATED MANAGEMENT OF MACROPHOMINA PHASEOLINA BY NATURAL RESOURCES OF HOT ARID REGION
INTEGRATED MANAGEMENT OF MACROPHOMINA PHASEOLINA BY NATURAL RESOURCES OF HOT ARID REGION S LODHA, RK AGGARWAL and SK SHARMA Central Arid Zone Research Institute, Jodhpur 342 003, India Background and objectives Macrophomina phaseolina (Tassi) Goid. is known to produce charcoal rot, root, stem and pod rot on more than 500 host plants in different parts of the world. Concurrent heat and water stress conditions during growing season favour occurrence of this pathogen in severe form on the crops grown under stressful conditions in hot arid regions of India. Since disease intensity in the field is outcome of inoculum density in the soil, major efforts were necessitated to bring down propagule density below the economic threshold levels. Concerned with the conservation of fast deteriorating environment, efforts in the past two decades were made to evolve eco-friendly management strategies to avoid dependence on expensive and hazardous chemical means of control. Materials and methods In the laboratory, large number of crop residues and oil-cakes were evaluated against the soil population density of M. phaseolina. In field experiments, efficacy of cruciferous residues combined with summer irrigation and/or soiarization was evaluated at 0-30 cm depth against M. phaseolina. In another field experiments, efficacy of composts and different moisture conservation practices was studied on dry root rot incidence, M. phaseolina and seed yield of ciusterbean. The population of M. phaseolina was determined by sprinkling 50 mg of soil on Chloroneb-Mercury-Rose bengal-Agar medium. Results and conclusions Utilizing natural resources of hot and region, two technological capsules were developed for the management of dry root rot. In resource affluent (water) farming system of arid region, amending cruciferous residues with summer irrigation/soil solarization significantly reduced the population of M. phaseolina at 0-30 cm soil depth. Intense solar irradiation and high ambient temperatures (42-47 oC) are characteristic features of hot arid region. The sharp decline in the viability of pathogenic propaguies could be attributed primarily to high soil temperatures. Further, incorporation of cruciferous residues in moist soil at high temperature facilitated greater release and action of sulphur-containing toxic volatiles like mercaptan, dimethyl sulphide and isothiocyanates, and microbial antagonism [1]. Once these volatiles, particularly isothiocyanates are released under prevailing high soil temperatures (46-53 oC), decomposed material also served as an amendment to enrich nutrient deficient sandy soils besides increasing moisture retention. Another beneficial consequence was rapid multiplication and activity of Bacillus firmus which induced suppressiveness in the soil. Cruciferous residues are amply available in the region due to large scale cultivation of Indian Mustard. This cost effective, environmentally sound and efficient method of control of M. phaseolina through natural resources is a novel approach of this kind in hot and regions. In a resource deficient (rainfed) farming, adoption of field resistant genotype, maintenance of low plant population and application of Farmyard manure only over seed furrows [2] and use of organic on-farm wastes as compost improved soil moisture conditions and fertility thereby encouraged microbial antagonism against M. phaseolina. Amendment of compost increased population of antagonist actinomycetes, lytic bacteria and nitrosomonas and decreased the population of M. phaseolina in soil. Enhancement in the population of antagonistic actinomycetes was of long term benefit because they are effective even under dry soils. Our efforts to inactivate pathogenic propaguies of Macrophomina during and after composting by bringing down C:N ratio of decomposing crop residues and than exposing freshly retrieved compost to prevalent summer heat reduced the chances of spreading this pathogen in the soil. Significant findings, their merits and practical implications are discussed in this paper. References 1. Gamliel A, Stapieton JJ, 1993. Phytopathology 83, 889-905. 2. Lodha S, 1996. Indian Phytopathology 49, 342-349.