Drought Hardening in Plant Breeding
Improvement in the drought tolerance ability of a genotype through various treatments is referred to as drought hardening. Two types of treatment are in common use for drought hardening. These are pre-sowing treatment and post sowing treatment.
Pre-sowing Treatment:
Seeds are treated before sowing to induce drought hardiness. Seeds are soaked in water for 24 hours and then sundried. The treated seeds are sown in the field. Plants developed from such seeds exhibit improved drought resistance or tolerance. The hardened plants exhibit higher yield under drought, higher water contents, increased viscosity of protoplasm , more bound water, higher metabolic rate and stronger roots. The same seed treatment, in sunflower, resulted in more stable metabolism of nitrogen ad phosphorous besides higher yield under drought conditions than unrelated plants. In barley , seed treatment was effective in improving drought tolerance of some genotypes, while it was ineffective for others. This indicated genetic differences for drought hardening. Seed treatment also improved drought tolerance in some genotypes of wheat. Various modifications of seed treatment method have been suggested by various workers.
Post –sowing Treatment:
The post-sowing treatment is given to the young seedlings. Mild drought stress in early stages of growth increase resistance to water stress under subsequent and more severe drought. In wheat and oats, such treatment was effective in improving drought resistance. However, cultivars differed in the hardening capacity in these crops. Several cycles of stress helped in identification of the most drought resistant and the most susceptible genotypes by measuring their survival.