this  article can helps you 

It helps with increased water uptake, water retaintion and also phosphate solubilisation

Drought is a major stress limiting the increase in the demand for food crops yet the world population is rapidly growing.Trichoderma spp. has been found to be associated with almost all natural ecosystems. They exist either in the rhizosphere or on plant

roots. They form a symbiotic relationship with the host plant. In the existence of the relationship, the proteome and transcriptome of plants change as a consequence of the interaction of Trichoderma metabolites or plant colonization. Alleviation of damage by reactive oxygen species (ROS), Water-use efficiency and Secretion of phytohormonal analogues are the three mechanisms employed by the fungi in enhancing plant growth under drought stress. Globally, studies clearly reveal that, the use of Trichoderma spp. under drought stress can effectively augment plant growth.

Trichoderma spp. form a symbiotic relationship with the host plant as early as the third phase of seed germination and this association lasts till the plant matures. Once the association has been established, systemic effects are induced in the host plant, so that while only roots are typically colonized, the effects also occur in leaves and in stems. The proteome and transcriptome of plants change as a consequence of the interaction of Trichoderma metabolites (Marra et al., 2006) or plant colonization (Bae et al., 2011). Thus, the fungi reprogramme plant gene expression, resulting in alteration of plant responses to their environment.

One of several reasons is that many Trichoderma isolates generate indole acetic acid, as mentioned above. This stimulates root production. For example, we have quantified a 40% increase in root mass of groundnuts, and a 50% increase in rice. In both cases, it enhanced drought tolerance because of the superior root system. Under ideal moisture conditions, this does not show up, but under stress it really does.

This effect is quite easy to measure: IAA in a petri dish cultures; and stimulation of root production in pots, or in the field. Sandy soils or media are easier to work with as clay is hard to wash off the roots.

Unfortunately, Ayanda, I could not evaluate Trichoderma mechanisms when I have inoculated it onto crops under drought stress, but all the agronomic/physiological variables measured clearly indicates that presence of this fungus in a combined inoculation is a key factor for plant growth improvement. Yet sometimes a simple fungal inoculation does not give suitable responses. Pls, take a look to the attached file. There are other related articles available in RG.