Comparative studies on the antagonistic activity of Trichoderma harzianum strains against Sclerotinia sclerotiorum (Lib.) de Bary of Chickpea (Cicer arietinum L.).

Abstract

Chickpea is the second most important pulse crop cultivated across the globe particularly in Asian and African countries. In India it’s one of the highest produced pulse crops followed by pigeon pea. It is an important protein-rich crop with considerable diversity that is either consumed whole or in the form of flour. Sclerotinia sclerotiorum (Lib.) de Bary is a soil borne plant pathogen that has got a very wide host range and infects over 400 plant species at all stages of growth and development. In chickpea it leads to non-specific wilting in grown-up plants and seedling mortality. Trichoderma spp. act as an effective bio-control agent for the management of myriads of plant pathogens affecting various crops at different stages of growth. The present study was conducted to determine the difference in the antagonism of Trichoderma harzianum strains SV-1, SV-2, SV-3, SV-14, SV-18 and IRRI-1 maintained in the lab with that of inoculated and re-isolated from soil after regular intervals along-with studying the effect of Trichoderma on the growth attributes of chickpea and disease incidence under pot conditions. Since, we know that the pathogenic cultures if maintained for a long time under artificial conditions tend to lose their virulence or suffer from attenuation, similarly in case of lab-maintained Trichoderma strains, which have been subjected to artificial culturing for a long time now, we intended to determine whether some degree of loss in their antagonistic potential over the same strains inoculated and re-isolated from their natural ecological niche existed or so. For this, two set of strains were maintained, one under in vitro conditions in lab and other set re-isolated from soil after 30, 60 and 90 days of inoculation. For both set of strains a comparative dual culture confrontation assay was carried out to determine the difference in antagonism of two sets. Re-isolated strains SV-1, SV-2, SV-14 and IRRI-1 exhibited excellent results via increase in the level of inhibition of mycelial growth of pathogen than their original strains maintained in the lab which clearly inclined the loss in antagonistic potential of Trichoderma harzianum strains, subjected to continuous artificial culturing. Seed treatment and soil application of strains SV-1, SV-2 and SV-14 considerably reduced the incidence of stem rot of chickpea under pot conditions. Trichoderma harzianum strains SV-1, SV-2 and SV-14 also proved to be the promising strains in improving the growth attributes like yield, plant height and fresh weight of chickpea, when mass multiplied over wheat grain and inoculated under pot conditions. Strain SV-18 and SV-3 acted as a weak performers in improving the growth attributes as well as reducing the disease incidence under pot conditions .Overall it was seen that Trichoderma harzianum strains maintained under artificial conditions for a long period of time witness reduction in potential of antagonism over the same strains inoculated and re-isolated after regular intervals from pot conditions, and the re-isolated strains that out-performed in inhibition of mycelial growth of pathogen also behaved to significantly improve the biometric parameters of crop thus concluding the fact that bioagents or any living entity exhibits its maximum biotic potential wholly and solely under its natural ecological niche.