Partitioning of dry matter during drought stress in rainfed lowland rice

Productivity of rice (Oryza sativa L.) in the rainfed lowlands depends not only on accumulation of dry matter, but also on its effective partitioning to grain. Partitioning of dry matter should be particularly important in such drought-prone environments, where dry matter production may be restricted. With late-season drought, an enhanced capacity to allocate dry matter to grain under water-deficit conditions should be advantageous. Field studies on dry matter partitioning under drought were conducted at eight locations in Chatfisgarh, India, between 1995 and 1998, using five diverse rice cultivars. Dry matter accumulation at flowering and maturity was significantly reduced in drought-affected sites. Variation was observed among cultivars in dry matter partitioning to grain under both favorable and water-stressed conditions. Drought stress at the reproductive stage significantly increased the dry matter partitioning from leaves and stems to grains in all cultivars. Under drought, dry matter partitioning into green leaves varied among cultivars, with NSG-19 partitioning the least dry matter to green leaves at maturity. Such a lower partitioning to green leaves at maturity during reproductive stage drought was associated with a higher remobilization of assimilates to fill the grains. Delay in flowering due to drought stress was negatively associated with grain yield and seemed to be governed by a lower plant water status. The contribution of dry matter partitioning from stems and leaves to grain filling increased with the severity of drought stress, particularly in cultivars with an enhanced capacity for leaf senescence during grain filling, which acted to stabilize their grain yields under drought