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During controlled water stress applied at the threeleaf stage, the barley ( Hordeum vulgare L.) cultivars ‘Proctor’ and ‘Excelsior’ showed different rates of free proline accumulation and leaf‐firing. Both processes were faster in Proctor (a drought‐susceptible cultivar) than in Excelsior (a drought‐resistant cultivar). The different rates of proline accumulation during stress in Proctor, in Excelsior, and in a wild barley ( H. spontaneum C. Koch) could be attributed to differences in the rate of decline of leaf water potential (ψ leaf ); at the same ψ leaf value, all three genotypes contained similar amounts of free proline. After non‐destructive screening of the F 2 generation from a Proctor ✕ Excelsior cross for proline‐accumulating capacity under controlled water stress conditions, F 3 seed from plants selected for high and low proline accumulation was obtained. When F 3 plants were tested for proline accumulation during controlled stress, the selection for proline accumulation was found to have been effective. Reselection among F 3 plants and subsequent testing of the F 4 generation confirmed this result. Among individual plants of the F 3 generation (which was segregating for the prollne accumulation trait) there was a positive association between the amount of free proline accumulated during stress and the severity of leaf‐firing. Massive proline accumulation is a symptom of severe internal water stress in barley and apparently has no survival value during drought. Although there is heritable variation in the amount of proline accumulated during stress, it is not of practical value in breeding for drought resistance.
Hanson et al. (Sun,) studied this question.