The Race to Flourish: Evaluating Natural Variation of Early Growth Rates in Rice

Abstract

Direct-seeded rice is a promising practice for sustainable rice productivity due to its ability to enhance ecosystem services. The use of rice varieties with shorter growth periods has become crucial for effective crop rotation. However, shorter growth periods often result in lower grain yields. Enhancing early growth in these short-duration rice varieties could help offset yield losses, but the genetic potential for early growth remains largely untapped. In this study, we investigated early growth in 90 rice genotypes under field conditions. Significant variation in plant growth was observed at 15, 25, and 35 days after sowing (DAS), with differences becoming more pronounced over time. Seed size had no significant effect on variation in growth rate. Hierarchical clustering analysis grouped the genotypes into five distinct growth patterns: Consistently Slow, Early Surge, Steady Moderate, Delayed Vigor, and Consistently Rapid. These patterns exhibited distinct trends in absolute growth rate (AGR) and relative growth rate (RGR). The Consistently Rapid and Early Surge groups showed higher early growth, whereas Delayed Vigor displayed accelerated growth at later stages. Contrary to traditional assumptions, the RGR during the early growth stage was not constant but varied significantly over time. RGR was primarily correlated with net assimilation rate (NAR) rather than leaf mass ratio (LMR) or specific leaf area (SLA). Size-standardized RGR and its components followed similar trends, indicating consistent growth dynamics across genotypes. These findings highlight distinct early growth patterns among rice genotypes, providing valuable insights for breeding programs aimed at improving early vigor and optimizing yield in short-duration rice varieties.