Apart from the direct inhibition of plant pathogens, Trichoderma spp. are reported to improve crop health by promotion of plant growth (both root an shoot). It is reported to enhance growth in a number of plant species like rice, wheat, sorghum, tomato, brinjal, soybean, chickpea, pea, rajma, chilli, capsicum, apple etc. However, this growth promotary effect was not only dependent on isolate of Trichoderma but also on plant species cultivar involved.
Plant growth promotion is one of the indirect mechanisms employed by Trichoderma spp. which plays a role in the biocontrol of various plant pathogens and in improvement of plant health. Treatment with Trichoderma generally increases root and shoot growth, reduces the activity of deleterious microorganisms in the rhizosphere of plants and improves the nutrient status of the plant. Growth enhancement by Trichoderma spp. has been observed even in the absence of any detectable disease and in sterile soil and is not considered to be a side effect of suppression of disease or minor plant pathogens. Secretion of hormone-like metabolites and release of nutrients from soil or organic matter, have been proposed as the mechanisms involved in plant growth promotion. Trichoderma harzianum is good solubilizer of phosphorus but different strains show wide variation in their ability to solubilize phosphorus. T. harzianum was also reported to solubilize MnO2, metallic zinc, and rock phosphate (mostly calcium phosphate) in a liquid sucrose-yeast extract medium. Trichoderma produced chelating metabolites and used redox activity for solubilizing the minerals. Both of these mechanisms also play a role in biocontrol of plant pathogens, and they may be part of a multiple-component action exerted by Trichoderma to achieve effective biocontrol under a variety of environmental conditions. It has observed that seed treatment of corn with T. harzianum, planted in low nitrogen soil resulted in plants that were greener and larger in the early part of the growing season. An increase in the microelement content (viz. Cu, P, Fe, Zn, Mn and Na) of plants was also observed.
Symbiotic colonization of roots by Trichoderma enhanced root growth, which may be responsible for increased tolerance of plans to biotic and abiotic stresses. Wheat plants raised from Trichoderma treated seeds tolerate drought (water stress) better under field condition.
In coming posts I shall be discussing on Apple production with respect to future perspective in Himachal Pradesh and High Density Plantation.