Annals of Applied Biology ISSN 0003-4746 RESEARCH ARTICLE Seed biopriming with drought tolerant isolates of Trichoderma harzianum promote growth and drought tolerance in Triticum aestivum N. Shukla, R.P. Awasthi, L. Rawat & J. Kumar Department of Plant Pathology, College of Agriculture, G.B. Pant University of Agriculture & Technology, Pantnagar, India Keywords Drought; free proline; osmotic potential; phenolics; photosynthesis; Trichoderma harzianum; wheat. Correspondence J. Kumar, Department of Plant Pathology, College of Agriculture, G.B. Pant University of Agriculture & Technology, Pantnagar 263 145, Uttarakhand, India. Email: jkumar@gmail.com Received: 21 June 2013; revised version accepted: 10 July 2014. doi:10.1111/aab.12160 Abstract Green house study was aimed to investigate the effect of seed biopriming with drought tolerant isolates of Trichoderma harzianum, viz. Th 56, 69, 75, 82 and 89 on growth of wheat under drought stress and to explore the mechanism under- lying plant water stress resilience in response to Trichoderma inoculation. Mea- surements of relative water content, osmotic potential, osmotic adjustment, leaf gas exchange, chlorophyll fluorescence and membrane stability index were per- formed. In addition, analysis of the phenolics, proline, lipid peroxidation and measurements of phenylalanine ammonia-lyase activity were carried out. Seed biopriming enhanced drought tolerance of wheat as drought induced changes like stomatal conductance, net photosynthesis and chlorophyll fluorescence were delayed. Drought stress from 4 to 13 days of withholding water induced an increase in the concentration of stress induced metabolites in leaves, while Trichoderma colonisation caused decrease in proline, malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ), and an increase in total phenolics. A common factor that negatively affects plants under drought stress conditions is accumu- lation of toxic reactive oxygen species (ROS), and we tested the hypothesis that seed biopriming reduced damages resulting from accumulation of ROS in stressed plants. The enhanced redox state of colonised plants could be explained by higher L-phenylalanine ammonia-lyase (PAL) activity in leaves after 13 days of drought stress in Trichoderma treated plants. Similar activity was induced in untreated plants in response to drought stress but to a lower extent in com- parison to treated plants. Our results support the hypothesis that seed bioprim- ing in wheat with drought tolerant T. harzianum strains increased root vigour besides performing the process of osmoregulation. It ameliorates drought stress by inducing physiological protection in plants against oxidative damage, due to enhanced capacity to scavenge ROS and increased level of PAL, a mechanism that is expected to augment tolerance to abiotic stresses. Introduction Plants during their lives are exposed to numerous stress factors, which significantly affect their growth. Of these, drought stress constitutes the highest percentage (26%) when the usable areas on the earth are classified for stress factors. It is followed by mineral stress (20%), cold and freezing stress (15%) and all the other stresses (29%) while only 10% area is not exposed to any stress factor (Blum, 1986). Plant experiences drought stresses either when the water supply to roots becomes difficult or when transpiration rate becomes very high. Lately, avail- able water resources for successful crop production are reportedly decreasing (Farooq et al., 2009). Furthermore, in view of various climatic change models suggested by scientists in many regions of world, crop losses due to increasing water shortage will further aggravate its impacts (Passioura, 2007). Ann Appl Biol (2014) 1 © 2014 Association of Applied Biologists