Exploitation of genetic variation for improvement of salt tolerance in spring wheat

Abstract

Considerable efforts have been made during the past few years to overcome the problem of soil salinity through the development of salt-tolerant lines of some important crop species. There is now much evidence available that variation both among and within a number of crop species in response to soil salinity is present and in most of cases is under genetic control. From a number of studies by different researchers it is also evident that spring wheat possesses a great magnitude of intra-specific variation for salt tolerance. However, in the present manuscript it is reported how further improvement in salt tolerance of spring wheat has been made by exploiting existing genetic variation. For this long-term program, we chose two known salt-tolerant cultivars, LU26S from Pakistan and Kharchia from India as the parents for different crossing programs for improvement of salt tolerance in spring wheat. After crossing them reciprocally their F₃ variable seed material (5,000 genotypes) was screened at two salt (NaCl) levels, 24 or 36 dS. m⁻¹. After the application of rigorous selection pressure at different growth stages, it was possible to select only one genotype at each salt level. These two selected genotypes were designated as S24 and S36 with respect to the salt level in which they were selected. Extent of improvement of salt tolerance in the two genotypes was assessed under greenhouse and field conditions with reference to their parents, a salt-tolerant line SARC-1, a salt sensitive line. S24 excelled all the cultivars/lines tested in terms of seed yield and yield components, but S36 was not significantly different from its parents in these attributes. Mechanism of salt tolerance in these genotypes, with particular reference to ion accumulation in different plant parts, water relations and gas exchange characteristics was also determined. The high salt tolerance in S24 was associated with its low accumulation of Na⁺ in the leaves. But in contrast, no clear-cut relationship between salt tolerance and photosynthetic capacity or water relation parameters in these genotypes was found.