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Abstract

Salt tolerance of three amphidiploid species, Brassica napus, B.carinata and B juncea with respect to their diploid parents, B.oleracea, B.nigra and B.campestris was investigated. Twenty three-day old plants of these six species were subjected for 28 days to salinized sand culture containing 0, 100 or 200 mol NaCl m™ in Hoagland's nutrient solution. All three amphidiploids produced significantly greater shoot fresh and dry matters, and sced yield than their respective diploid parents under saline conditions. B.napus being the highest followed by B.carinata and Bjuncea of all the species. Of the diploid parents B.nigra was the lowest followed by B.oleracea in terms of relative shoot biomass since the plants of the former species subjected to the highest salt concentration did not survive till maturity. A close association was found between growth and CO, assimilation rate (A) for all species differing in degree of salt tolerance. Stomatal conductance (g) was reduced due to salt stress in all the species but this variable had no significant correlation with assimilation rate. However, the amphidiploid species had significantly greater photosynthetic rate, water use efficiency (A/E), intrinsic water use efficiency (A/g) than those of their diploid parents. Parallels were drawn between data for ion accumulation in different plant parts and salt tolerance of the Brassica species. All three diploid parents had significantly higher Na' but lower K* in the shoots at all external salt regimes as compared with that of amphidiploid species. The same pattern was observed for root K°. The shoot Cal" decreased considerably in B.nigra and B.oleracea and increased in B.napus at the highest salt regime, whereas in the other species no effect of salt was observed on shoot Ca"concentration. Shoot CI was the lowest in the salt tolerant B.napus of all the species, whereas the difference among the other species for this ion was not consistent. All three amphidiploids maintained significantly higher K/Na and Ca/Na ratios in the shoots compared with the diploid species, in conclusion, high salt tolerance of the amphidiploids war associated with & high assimilation rate, water use efficiency, intrinsic water use efficiency and shook-/Na and Ca/Na ratios and partial exclusion of Na" from the shoots. In contrast, there was linle association of the tolerance of these species with stomatal conductance, leaf water potential or transpiration rate (E). The salt tolerance trait in amphidiploid species seemed to have been inherited from the diploid species B.campestris and B.oleracea with genomes A and C, respectively.

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