ADAPTATION VERSUS PRE-EXISTING RESISTANCE: AN INTERGENOTYPE ANALYSIS OF THE RESPONSE OF SORGHUM BICOLOR TO SALINITY

Abstract

Developmental and physiological responses of 11 Sorghum bicolor (L.) Moench genotypes exposed for 3 weeks to a 150 mM NaCl-pretreatment were studied. Following the pretreatment, exposure to 300 mM NaCl resulted in a gradient of response between “adaptation to salinity” (increase in salinity tolerance) and “pre-existing resistance” (maintenance of original salinity tolerance). Level of adaptation of each genotype was quantified by determination of the mean relative growth rate of the shoot at 300 mM NaCl ( ). There was a positive correlation between and the following parameters during the process of adaptation: inhibition of growth, decrease of the shoot:root ratio, and shoot Na + uptake. There were more pronounced physiological perturbations during adaptation than during the pre-existing resistance response to salinity. During the first 25 days of exposure to NaCl, inhibition of growth and shoot Na + concentration were not correlated. The much lower value for the intergenotype coefficient of variation (ICV) for Na + + K + as compared to that for Na + or K + suggests that the sum of these ions is a parameter of physiological importance, and that these two ions were interdependent and partially interchangeable. It seems that Na + + K + + CI − were the main osmotica in the shoot of most genotypes. It is concluded that the nature of the response of the plant, rather than Na + toxicity, was responsible for the effects of salinity on growth.