Gradient in vitro Testing of Tomato (Solanum lycoersicon) Genotypes by Inducing Water Deficit: A New Approach to Screen Germplasm for Drought Tolerance

A new concept was tested for screening germplasm under in vitro condition using Polyethylene Glycol (PEG-6000) under 2 induced stress conditions by developing gradient with two replications in factorial CRD in MS medium. Important seedling growth parameters were recorded. Drought resistant mutant derivatives performed significantly superior for root characters over cultivated genotypes. Decrease in seedling growth was worth notice with increasing concentration of PEG indicating precise nature of in vitro screening. Under normal environment also, mutant exhibited better seedling growth than cultivated genotypes in respect to root traits with higher magnitude of initial stress root growth was severely retarded. Initially mild and later on increasing stress exhibited more root growth and reduced vegetative growth indicating assimilate translocation more towards root growth than shoot growth. In general mutant derivatives performed better than cultivated genotypes under all levels of water stress. This new screening method validated mutants to be drought tolerant at all levels of water stress. These in vitro studies were complemented by screening all genotypes under field condition and similar performance was observed for drought tolerance. This new Gradient in vitro (GIV) screening method may prove to be potential to study response of genotypes under stress.