DROUGHT AND SALT TOLERANCE ARE NOT NECESSARILY LINKED - A STUDY ON WHEAT-VARIETIES DIFFERING IN DROUGHT TOLERANCE UNDER CONSECUTIVE WATER AND SALINITY STRESSES

Hydroponically-grown seedlings of two bread-wheat (Triticum aestivum L.) varieties (Kobomugi: drought tolerant, Regina: drought and salt sensitive) were evaluated for drought (PEG 4000) and salt (NaCl) tolerance under controlled environmental conditions. Changes in net photosynthesis (A), stomatal conductance (g(s)), specific leaf area (SLA), abscisic acid content (ABA), and water content of shoots (W-s) and roots (W-r) were measured. Osmotic pressures of the culture solutions were 0.25 [11% PEG(1)] and 1.0 MPa [21% PEG(2)]. After the 7 days of exposure, control and PEG treated plants were transferred to equi-osmolal. [i.e. with PEG(1) and PEG(2)] NaCl culture solutions. Throughout the PEG induced drought stress, the leaves of Kobomugi exhibited lower stomatal conductance (g(s)) and higher leaf ABA content than those of Regina. However, net photosynthesis (A) was similar for both varieties. Thus, Kobomugi possessed a higher water use efficiency (WUE) than Regina. Following the transfer of the plants from control to saline culture solution g(s), A, WUE, SLA, W-s, and W-r in Kobomugi were not significantly different from those in Regina. Based on these results Kobomugi can be considered as susceptible as Regina for high salinity. Transfer from PEG(2) to equi-osmolal NaCl(2) nutrient solution resulted in a steady increase in both A and g(s) in Regina, though in Kobomugi both A and g(s) declined dramatically after an initial increase. So, as a consequence of the consecutive occurrence of water and salt stresses the drought tolerant Kobomugi was more retarded than the drought sensitive Regina. The possible disadvantage of a genotype only possessing the traits that enable it to be a <<water saver>> without any obvious ability to cope with the toxic effect of ions, when water limitation is followed with salinity imposed stresses, is discussed.