Genetic variation in tolerance to the osmotic stress componentof salinity stress in durum wheat

Salinity affects plant growth by the osmotic stress of the salt around the roots as well as by toxicity caused by excessive accumulation of salt in leaves. The aim of this study was to determine whether there is significant genetic variation in tolerance to osmotic stress that can be useful in improving the salinity tolerance of crop plants. Durum wheat is a salt-sensitive crop whose yield is reduced by moderately saline soils. Genetic variation in tolerance to osmotic stress in durum wheat was examined in 50 international durum varieties and landraces by measuring the response of stomatal conductance to salt stress before salts built up in the leaf. Stomatal conductance is a sensitive indicator of the osmotic stress because it is reduced immediately with the onset of salinity, and is the initial and most profound cause of a decline in CO₂ assimilation rate. Genetic differences of 2-3-fold were found in the magnitude of the response of stomatal conductance to salt-induced osmotic stress. Higher stomatal conductance in salt related to higher CO₂ assimilation rate. There was a positive relationship between stomatal conductance and relative growth rate in salt. This study shows the potential for new genetic gains in salt tolerance in durum wheat.