Capacity for Proline Accumulation During Water Stress in Barley and Its Implications for Breeding for Drought Resistance1

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Abstract
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 (ψleaf); at the same ψleaf value, all three genotypes contained similar amounts of free proline.After non‐destructive screening of the F2 generation from a Proctor ✕ Excelsior cross for proline‐accumulating capacity under controlled water stress conditions, F3 seed from plants selected for high and low proline accumulation was obtained. When F3 plants were tested for proline accumulation during controlled stress, the selection for proline accumulation was found to have been effective. Reselection among F3 plants and subsequent testing of the F4 generation confirmed this result.Among individual plants of the F3 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.