Effect of abiotic stress on phosphate solubilization by biocontrol fungus Trichoderma sp.

This study was undertaken to explore the role of Trichoderma sp. in phosphate (P) solubilization and antagonism against fungal phytopathogens. All fungal isolates (SE(6), KT(6), KT(28), and BRT(11)) and a standard culture of T. harzianum (Th-std) were able to antagonize two fungal phytopathogens (Sclerotium rolfsii and Rhizoctonia solani) of chickpea (Cicer arietinum L.) wilt complex. Transmission electron microscopic studies (TEM) further confirmed ultra-cytological changes in the sclerotia of S. rolfsii parasitized by Trichoderma sp. All fungal cultures exhibited production of NH(3) and siderophore, but only BRT(11), SE(6), and Th-std could produce HCN. Among all the cultures tested, isolate KT(6) was found to be most effective for solubilization of ferric phosphate releasing 398.4 μg ml(-1) phosphate while isolates BRT(11) and SE(6) showed more potential for tricalcium phosphate (TCP) solubilization releasing 449.05 and 412.64 μg ml(-1) phosphate, respectively, in their culture filtrates. Part of this study focused on the influence of abiotic stress conditions such as pH, temperature, and heavy metal (cadmium) on phosphate (TCP) solubilizing efficiency. Two selected cultures KT(6) and T. harzianum retained their P solubilizing potential at varying concentrations of cadmium (0-1000 μg ml(-1)). Isolate KT(6) and standard culture of T. harzianum released 278.4 and 287.6 μg ml(-1) phosphate, respectively, at 1000 μg ml(-1)cadmium. Maximum solubilization of TCP was obtained at alkaline pH and at 28°C temperature. Isolate BRT(11) was found most alkalo-tolerant releasing 448.0 μg ml(-1) phosphate at pH 9.