Inducing drought tolerance in rice by salinity osmohardening

Drought-tolerant rice is a rare commodity and may not be available in the near future. Inducing rice to be drought-tolerant can be an alternative. Hardening rice seedlings before transplanting will make it vigorous and able to withstand most stresses in the field. Salinity can harden off rice seedlings and may induce drought tolerance. This hardening of rice seedlings using salt solution is referred to as 'osmohardening'. This study aims to determine the effect of initial salinity stress on rice seedlings in response to drought stress at the vegetative growth. Specifically, the objective is to determine if salinity stress can act on osmohardening rice seedlings in preparation for drought stress at a later stage. IR29, IR64, and IR66946-3r-178-1-1 (f1 478), salinity-sensitive, moderately tolerant and tolerant accessions, respectively, were used. After exposing the plants to a mild saline condition (ec=6 and 8 ds/m) for 2 wk, moderate drought stress was imposed until panicle initiation, these were then irrigated until harvest. Results showed that IR64 was the tallest and has the most number of tillers, but it flowered last. F1 478 had the highest grain yield. Plants affected by drought were stunted, had fewer tillers, rolled leaves, delayed flowering, and less grain yield. The osmohardening seedlings subjected to drought performed better then did the unsalinized seedlings, indicating that any adaptive mechanism triggered by salinity stress is carried over by the plants all the way to the drought stress condition. These reports are supported by reports that these two stresses affect plants in overlapping but not identical ways, and that there is an overlap of about half the genes induced or inhibited by high-salinity stress and drought in rice (Bartels and Sunkar 2005). The present study provides preliminary evidence that drought tolerance in rice can be induced by salinity osmohardening. Further test shall be conducted to determine the applicability of this result in the field.