A Uniform, Objective, and Adaptive System for Expressing Rice Development

The large area of rice ( Oryza sativa L.) production worldwide is critical to the well being of large numbers of the world's people. Yet for rice, the most important single plant species for human nutrition, there is not a widely used growth staging system. Despite good points of the published rice growth staging systems, none has been used widely for describing rice growth and development. Consequently, an objective growth staging system with enumeration adapted to cumulative leaf number (CLN) would improve communication among scientists, farmers, and educators. We propose a rice developmental staging system divided into three main phases of development: seedling, vegetative, and reproductive. Seedling development consists of four growth stages: unimbibed seed (S0), radicle and coleoptile emergence from the seed (S1, S2), and prophyll emergence from the coleoptile (S3). Vegetative development consists of stages V1, V2 … V N ; N being equal to the final number of leaves with collars on the main stem. Reproductive development consists of 10 growth stages based on discrete morphological criteria: panicle initiation (R0), panicle differentiation (R1), flag leaf collar formation (R2), panicle exertion (R3), anthesis (R4), grain length and width expansion (R5), grain depth expansion (R6), grain dry down (R7), single grain maturity (R8), and complete panicle maturity (R9). Assigning rice growth stages based on discrete morphological criteria will result in unambiguous growth‐stage determination. For example, using this system, two people staging the same plant will arrive at the same growth stage. This is because the system exploits the presence or absence of distinct morphological criteria in a symbolic logic dichotomous framework that only permits yes or no answers.