Salt-tolerance in Brassica juncea L. I. In vitro selection, agronomic evaluation and genetic stability

Abstract

In vitro selection of salt tolerant plants of Brassica juncea L. (Indian mustard) cv . Prakash has been accomplished by screening highly morphogenic cotyledon explant cultures on high NaCl media . Out of a total of 2,620 cotyledons cultured on high salt medium, 3 survived, showed sustained growth and regenerated shoots . They were multiplied by axillary bud culture on NaCl free medium . The salt-selected shoots retained salt tolerance following 3 month of growth and multiplication on control medium . While two of these somaclones flowered and set seeds, third one grew slowly, had abnormal leaf morphology and was sterile .The seed of the two fertile plants were sown in the field to raise R, segregating generation . Data were recorded for field, other agronomic components and oil content . The somaclonal lines, both selected salt-tolerant and non-selected, showed tremendous amount of variation for all the characters studied . One of the two tolerant somaclones invariably showed reduced height, longer reproductive phase and higher 1000 seed weight . Based on the agronomic performance of R, plants of these somaclones, some plants were selected and their progeny were evaluated for agronomic performance under standard field conditions and salt-tolerance in the greenhouse using sand pot culture method . Most of the lines bred true for their specific characteristics . In the greenhouse, selected salt-tolerant somaclones (SR-2 and SR-3) performed better for plant growth, yield and other agronomic traits at higher salt treatments, indicating thereby that salt-tolerance trait selected in vitro was expressed in the whole plants and is genetically stable and transmitted onto the progeny . The two tolerant lines, however, differed in their salt-tolerance during vegetative and reproductive phases as indicated by their salt-tolerance and stress susceptibility indices . The mechanism of salt-tolerance is not clear and needs to be further investigated .

Tissue Culture in the Improvement of Salt Tolerance in Plants

“…Until now, efforts to exploit the potential of somaclonal variation to improve salt tolerance in plants have been restricted to cell selection approaches that are based primarily on empiricism (Nabors et al 1980;Bhaskaran et al 1986;Bressan et al 1987;McHughen 1987;Narayanan and Sree Rangasamy 1989;Vajrabhaya et al 1989;Freytag et al 1990;Jain et al 1990;Tal 1990;Waskom et al 1990). It is not possible to ascertain exactly what determinants of salt tolerance have been selected and what is the interrelationship, if it exists, between these determinants and reduced agricultural productivity.…”

“…Selection in vitro also results in the isolation of cells that express enhanced salt tolerance after the stress is eliminated and the phenotype is stable through regeneration (Mathur et al 1980;Nabors et al 1980Nabors et al , 1982Tyagi et al 1981;Yano et al 1982;Bressan et al 1985Bressan et al , 1987Nabors and Dykes 1985;Bhaskaran et al 1986;Pua and Thorpe 1986;McCoy 1987b;Bouharmont and Dekeyser 1989;Hanning and Nabors 1989;Narayanan and Sree Rangasamy 1989;Vajrabhaya et al 1989;Freytag et al 1990;Jain et al 1990Jain et al , 1991Waskom et al 1990;Watad et al 1991b). Difficulties in isolating cells that possess a genetic capacity to tolerate high salt concentrations from those that are exhibiting an inherent capacity for adjustment into saline environments have been circumvented either by isolating cell clones or through establishment of selection protocols capable of identifying cells with a genetically based predisposition for salt tolerance (Dix and Street 1975;Nabors 1983Nabors , 1990Bressan et al 1985;van Swaaji et al 1986;Ochatt and Power 1988;Tal 1990).…”

“…Regardless, it seems clear that plants can be regenerated from cultures growing in vitro that exhibit greater salt tolerance than the original genotypes. Somaclonal variation for salt tolerance has been determined to be inherited in the progeny of tobacco (Nabors et al 1980;Bressan et al 1987), sorghum (Bhaskaran et al 1986;Waskom et al 1990), flax (McHughen 1987), rice (Vajrabhaya et al 1989;Narayanan and Sree Rangasamy 1989), Brassica juncea (Jain et al 1990), alfalfa (Winicov 1991), and sugar beet (Freytag et al 1990) including selections that exhibit enhanced salt tolerance in the R 4 generation. These results seem to indicate that intrinsically cellular mechanisms that are selected for in vitro will confer an enhanced salt tolerance phenotype to regenerated plants.…”

Salt-tolerance in Brassica juncea L. II. Salt-stress induced changes in polypeptide pattern of in vitro selected NaCl-tolerant plants

“…Such resistant cell lines are potentially useful in the identification of salt tolerance related polypeptides. We have selected genetically stable salt-tolerant plants of Indian mustard (Brassica juncea L.), an important oil-seed crop, by screening in vitro the highly morphogenic cotyledon explant cultures on high NaC1 media (Jain et al, 1990;1991a). The selected plants had higher rates of osmoregulation (Jain et al, 1991b) and performed better for biomass, seed yield and oil content as compared to the parent and a non-selected line under salt-stress (Jain et al, 1990).…”

“…We have selected genetically stable salt-tolerant plants of Indian mustard (Brassica juncea L.), an important oil-seed crop, by screening in vitro the highly morphogenic cotyledon explant cultures on high NaC1 media (Jain et al, 1990;1991a). The selected plants had higher rates of osmoregulation (Jain et al, 1991b) and performed better for biomass, seed yield and oil content as compared to the parent and a non-selected line under salt-stress (Jain et al, 1990). In this communication, we report the saltstress effected changes in electrophoretic polypeptide pattern of seedlings, leaves and siliqua tissue of in vitro selected salt tolerant variants (SR-2 and SR-3), a non-selected somaclonal line (CP-5) and parent cv.…”