Abstract
Eight different wheat cuItivars were exposed to soil moisture stress at preheading stage in a net-house with glass top. On the basis of absolute grain yield, the cultivar LYP-73 was the most tolerant, while R-S was the most sensitive to drought at preheading stage. The genotype R-S suffered about 28% loss in grain yield mainly attributable to 'decreased grain weight. Polyethylene iycol (PEG) induced water stress (-i3 bar) caused more decrease of fresh weight in LU-.26S than Pak-81, The role of osmoregulaion in drought tolerance is discussed.
INTRODUCTION
Plants growing in water limited environments adapt and/or acclimatize in a variety of ways via mechanis.ms that originate at the subcellular level (Jordan, 1983). Osmotic adjustment (large change i n 00 solute content) occurs in response to soil moisture availability and permits plants to maintain growth on 'limited sail water when growth otherwiie would not occur (Boyer, 1983). Growth is enhan-ced in plant ,genotypes having superior osmotic adjustment as soils become dry. About one-third of the total area under wheat in Pakistan falls in the rainfed regions where rainfall, particularly at the prtheading stage, is often very low `and wheat crop faces water deficit at this critical stage of grain development. The purpos
