Characterization of Somaclones of Medicago sativa L. for Drought Tolerance

Water stress is a serious environmental problem throughout the world. It is a conse-quence of both drought and salinity which may be relieved by breeding cultivars that can tolerate low soil water potentials. Alfalfa (Medicago sativa L.) is normally grown in arid and semi-arid zones. One approach to improving the ability of the crop tolerate drought is to make use of the variation provided by tissue culture derived from somaclonal varia-tion. Seedlings of a moderately salt tolerant line CUF ۱۰۱-۱S derived from the commercial variety CUF ۱۰۱ were used as a source of explants to initiate and regenerate tissue cul-tures. Regenerant plantlets were allowed to grow to maturity, selfed, and set seed. These seeds (R۱) were germinated and grown in a nutrient medium containing ۰, ۲۰۰ and ۲۵۰ g l-۱ polyethylene glycol (PEG) ۶۰۰۰ and additional calcium as CaCl۲ (۴.۰ mol m-۳) for ۱۴ days to assess their ability to withstand stress in the progeny generation. Tolerance to PEG was assessed using measurements of root and shoot lengths. Proline levels and activ-ity of the antioxidant enzymes, catalase (EC ۱.۱۱.۱.۶) and glutathione reductase (GR) (EC ۱.۶.۴.۲) were also determined. Selected somaclones were more tolerant than the parent. A large increase in the level of proline was observed in the somaclones compared with the parent variety in response to PEG stress. The activity of catalase and glutathione reduc-tase increased in the tolerant genotypes but remained unchanged in the parent when they were subjected to PEG stress.

Keywords:

Tissue culture , Proline , drought , Antioxidant , Medicago sativa