Physiological traits of hybrid rice for high grain yield in the wet season: analysis of characters related to lodging

Lodging is a chronic constraint limiting rice yield in high-yielding environments. Cultivar selection is one way of preventing lodging. Lodging behavior and yield potential of 16 rice genotypes, including 12 hybrids, 3 inbreds, and 1 new plant type (NPT), were studied at the International Rice Research Institute [Los Banos, Laguna, Philippines] farm under optimum crop management to achieve maximum attainable yields during the wet season of 2004. Yield and yield components were determined at maturity. Growth analyses were conducted at key growth stages to determine crop growth rate (CGR), leaf area index (LAI) and specific leaf weight. Culm characters related to lodging were determined at 30 days after flowering and degree of lodging was determined at maturity. IR76712 H produced the highest yield (7.6 t/ha), followed by IR75217 H and Magat, which produced 7.5 t/ha. The hybrids exhibited greater CGR than the other cultivars. The hybrids showed higher LAI, which might be attributed to greater CGR. Distinct genotypic differences in characters related to lodging were observed. The lodging index (bending moment/breaking resistance x 100, a distance between fulcra of 5 cm) of the highest-yielding genotypes (IR76712H, IR75217H, and Magat) at the 4th internode from the top (N4) at maturity was more than 200. High yield of these genotypes was obtained under quite dangerous conditions of lodging. The reason for increased lodging index at N4 of these genotypes was low breaking resistance. The degree of lodging was also high for these genotypes at maturity. This could be caused by a high rate of translocation of dry matter from culm and leaf to panicle and a decrease in N4 culm dry weight at maturity. The hybrids SL-10H, SL11H, and NPT showed higher breaking resistance and subsequently lower lodging index, but also had lower grain yield. To obtain high yield in high yielding environments, it is necessary to develop cultivation techniques to balance the translocation of dry matter from the culm and leaf sheath to the panicle.