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

1980), the BBCH system (Lancashire et al., 1991), and Haun (1973). Zadoks et al. (1974) is an adaptation of The large area of rice (Oryza sativa L.) production worldwide is Feekes’ (1941) scale (with 23 subdivisions) but further critical to the well being of large numbers of the world’s people. Yet delineated. The IRRI (1980) scale is a 10-point system for rice, the most important single plant species for human nutrition, there is not a widely used growth staging system. Despite good points (0–9) with no subdivisions. The BBCH (Lancashire et of the published rice growth staging systems, none has been used al., 1991) system for rice is an adaptation of the Zadoks widely for describing rice growth and development. Consequently, et al. (1974) scale. Consequently, the BBCH and Zadoks an objective growth staging system with enumeration adapted to cuet al. scales are 99 and 110 point systems, respectively. mulative leaf number (CLN) would improve communication among Haun (1973) also described a wheat (Triticum aestivum scientists, farmers, and educators. We propose a rice developmental L.) developmental system that has been applied to rice. staging system divided into three main phases of development: seedHaun’s system is enumerated into CLN. All four sysling, vegetative, and reproductive. Seedling development consists of tems have strengths and all share problems related to four growth stages: unimbibed seed (S0), radicle and coleoptile emerenumeration of growth stages and criteria for the detergence from the seed (S1, S2), and prophyll emergence from the coleopmination of the growth stage. Despite good points of tile (S3). Vegetative development consists of stages V1, V2 . . . VN; N being equal to the final number of leaves with collars on the main the published rice growth staging systems, none has stem. Reproductive development consists of 10 growth stages based been used widely for describing rice growth and develon discrete morphological criteria: panicle initiation (R0), panicle opment. differentiation (R1), flag leaf collar formation (R2), panicle exertion Terms that have been used to describe plant develop(R3), anthesis (R4), grain length and width expansion (R5), grain mental time include plastochron and phyllochron. Plant depth expansion (R6), grain dry down (R7), single grain maturity age can be expressed in a biologically meaningful way by (R8), and complete panicle maturity (R9). Assigning rice growth the CLN produced on the main stem. The time interval stages based on discrete morphological criteria will result in unambigubetween successive leaf initiations is called a plastochron ous growth-stage determination. For example, using this system, two (Langer, 1972). The problem with determining the plaspeople staging the same plant will arrive at the same growth stage. tochron is that the initiated leaves are not visible without This is because the system exploits the presence or absence of distinct morphological criteria in a symbolic logic dichotomous framework microscopy. A phyllochron is the time interval between that only permits yes or no answers. the same leaf developmental events of successive leaves (Rickman and Klepper, 1995; Wilhelm and McMaster, 1995; Nemoto et al., 1995). The concept of plant age by CLN was implicitly recogR grain is a food staple for more people than foods obtained from any other single plant species. nized by Bonnet, Kepler, Leonardo da Vinci, and perhaps Aristotle (Jean, 1994). The incorporation of plant Major portions of the world obtain more than half of their daily dietary calories from rice. Consequently, rice age (as determined by CLN) into developmental systems has been progressive. Feekes (1941) essentially research and its application potentially affects the well being of a large part of the world’s human population. ignored the delineation of vegetative growth into phytomers in his system for wheat. Higgins et al. (1964) Biological understanding and practical value of crop growth staging systems have been progressive and cureported on CLN as a means of expressing plant age. Hanway (1963, 1966) recognized that corn (Zea mays mulative. Crop growth staging systems are meant to be an aid in information transfer for crop management. L.) develops by CLN but did not enumerate his stages by CLN. Rather, he stayed with the enumeration proThey can also aid scientists and others in observing, recording, and communicating critical crop growth data. posed by Feekes (1941). However, Hanway did recognize CLN to a degree in his corn system. Haun (1973) Yet for rice, the most important single plant species for human nutrition, there is not a widely used growth appears to have been the first to incorporate CLN into the enumeration of a crop growth staging system. Haun staging system. We found four published systems for describing rice development: Zadoks et al. (1974), IRRI recognized the modular nature of vegetative development for wheat and allowed his enumeration to be set by the plant, that is by the CLN (x in Haun’s system), Paul A. Counce, University of Arkansas, Rice Research and Extension rather than an arbitrary number (e.g., 10, 11, 99, or Center, P.O. Box 351, Stuttgart, AR 72160; Terry C. Keisling, Univer110). The discrete aspect of Haun’s wheat development sity of Arkansas, Northeast Research and Extension Center, P.O. Box system was combined with the continuous criteria of 48, Keiser, AR 72351 and Andrew J. Mitchell, Stuttgart National Aquaculture Research Center, P.O. Box 860, Stuttgart, AR 72160. the partial development of elongating leaves. Fehr and Paper no. 99001 published with the approval of the Director, AgriculCaviness explicitly recognized CLN and incorporated tural Experiment Station, University of Arkansas, Fayetteville, AR three important advances into their soybean [Glycine 72701. This research was supported by a grant from the Arkansas max (L.) Merr.] growth staging system: Rice Research and Promotion Board. Received 10 Feb. 1999. *Corresponding author ([email protected]). Abbreviations: CLN, cumulative leaf number; IE, internode elongation. Published in Crop Sci. 40:436–443 (2000).