The beneficial effect of reduced elongation growth on submergence tolerance of rice

Adverse effects of elongation growth on tolerance to complete submergence for up to 14 d were evaluated in rice seedlings of cultivars which differed in submergence tolerance. There is a good negative correlation between per cent survival and elongation growth of genotypes during complete submergence (r = -0.81), When elongation growth underwater is minimized by application of a gibberellin biosynthesis inhibitor, per cent survival increases by as much as 50 times for one cultivar. These effects are likely related to elongation growth since (i) addition of gibberellin had the opposite effect by reducing survival, and (ii) when the elongation inhibitor and gibberellin were added together, there was no effect on elongation growth and the per cent survival did not change. A GA-deficient mutant of rice which had little elongation ability during submergence showed a high level of submergence tolerance when plants were submerged at equal initial dry weights and carbohydrate levels relative to a submergence-tolerant cultivar. These results are consistent with the hypothesis that elongation growth competes with maintenance processes for energy and hence reduces survival during submergence. The impact of these findings is that in environments where elongation ability is not required, there is a potential to increase submergence tolerance of agriculturally important cultivars by selecting for least elongation, at least during periods of complete submergence. Furthermore, this trade-off between stimulated elongation growth and submergence tolerance will have important ecological consequences for the distribution of plant species in different flood-prone environments.