Variation in Salt Tolerance and Ion Accumulation among Subterranean Clover Cultivars

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Abstract
Increased productivity of forage crops under saline conditions is a desired characteristic in irrigated areas in both the USA and Australia. Clover (Trifolium) species are often used in single or mixed stands. Studies were conducted to determine physiological mechanisms and the extent of variability for salt tolerance among cultivars of subterranean clover. Six cultivars of subterranean clover (T. subterraneum L.) belonging to three different subspecies, brachycalycinum (cv. Clare and Wenijup), subterraneum (cv. Bacchus Marsh and Tallarook), and yanninicum (cv. Meteora and Trikkala), were tested for salt tolerance during germination and emergence and at the vegetative stage of growth in sand cultures salinized with 20 to 80 mM NaCl. Cultivars differed in final emergence, growth rates, salt tolerance, and ion accumulation. When salinity was applied at the time of seeding, the cultivars Clare and Tallarook were the most tolerant. When plants were salinized after the three‐ to four‐trifoliate leaf stage, Clare had the highest relative salt tolerance as defined by shoot dry weight yield reduction as a percent of the unsalinized controls. Relative salt tolerance followed the order Clare > Bacchus Marsh = Trikkala = Tallarook > Meteora = Wenijup. Meteora had the highest productivity as defined by total dry weight production under high NaCl treatment. Productivity of clover under saline conditions requires high growth potential and low reduction in yield with increasing salinity. High productivity under salinity stress was positively correlated with restricted Na+ uptake in the shoot and the maintenance of high K+/Na+ ratios.
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