Salt tolerance of rapid‐cycling brassica species in relation to potassium/sodium ratio and selectivity at the whole plant and callus levels

Abstract

The potassium/sodium (K/Na) ratio in the shoots of six rapid‐cycling Brassica species was greatly reduced by seawater salinity. It proportionally decreased with increasing salinity from 4 dS/m to 12 dS/m. This decrease was correlated with salt‐induced growth reduction (expressed as the percentage of control) within a species. The change in K/Na ratio with increasing salinity, however, was not correlated with K‐Na selectivity. The change in K/Na ratio at the callus level corresponded to that at the whole plant level. Both K/Na ratio and K‐Na selectivity were not found to be correlated with the relative salt tolerance of these Brassica species, indicating that the maintenance of a high K/Na ratio as a mechanism for salt tolerance in these Brassica species was not operative. These results also suggest that a high shoot K/Na ratio or K‐Na selectivity may not be reliable selection criteria for salinity resistance in some species.