Spikelet and Floret Naming Scheme for Grasses with a Spike Inflorescence

Effective schemes to name uniquely and d e h e parts of grass plants allow researchers to communicate results of their experiments accurately and precisely. Naming schemes for vegetative parts of grass plants have been developed; however, no system exists to name uniquely parts of the inflorescence. In this report, we present a method to extend existing systems to name parts of grass spikes. Spikelet positions are denoted by the letter S and numbered acropetally along the rachis. For example, the third spikelet position from the base of the rachis is named S3. Likewise, floret positions along the rachilla are named F (or C after fertilization) and numbered acropetally from the base to tip. The second caryopsis (floret) in the spikelet at the third spikelet position on a spike would be named S3C2. This simple scheme, when combined with the system for naming tiller, leaves, and roots, will allow all plant parts to he named uniquely. If the caryopsis in the previous example was produced on the tiller formed in the axil of the first leaf on the main stem, the complete description of the caryopsis is TlS3C2. Using this system, researchers and practitioners can communicate precisely findings on development, growth, and functional characteristics of plants and plant parts. S IMILAR SYSTEMS for naming uniquely vegetative parts of small grains and forage grasses have been devised by Jewiss (1972) and Klepper et al. (1982) for leaves and by Jewiss (1972) for tillers. The combination of these systems, along with modification or extension by others (Fraser et al., 1982; Kirby et al., 1985; Klepper et al., 1983a; Masle, 1985 ; Masle-Meynard and Sebillotte, 1981; Thomson and Stokes, 1987) has produced the standard system for naming and identifying vegetative parts of small grains and forage grasses. The system is based on the concept of naming structures on a culm with a letter to designate the structure type and numbering them in the order of their appearance. That is, the first leaf on a culm is designated L1, L for leaf and 1 for the first position. The second leaf is designated L2. The W.W. Wilhelm, USDA-ARS, 117 Keim Hall, Univ. of Nebraska, Lincoln, NE 68583-0934; Gregory S. McMaster, USDA-ARS, Great Plains Systems Res. Unit, PO Box E, Fort Collins, Colorado 80522. This paper is a joint contribution of the USDA-ARS and the Agric. Res. Division of the Univ. of Nebraska. Published as J. Series Number 11 191. Received 11 July 1995. *Corresponding author ([email protected]). Published in Crop Sci. 36: 1071-1073 (1996). system extends up the culm so all leaves can be named specifically. Culms, or tillers, are denoted with a T and defined by the number of the leaf axil in which they form, with the exception of MS, which is the first culm to appear from the seed. Primary, or first-order tillers, are formed in the axils of MS leaves and designated by one-digit numbers (e. g . , T 1). Second-order tillers are born in the axils of leaves on first-order tillers and are named with a T and two-digit numbers (e.g., T21). The system is infinitely expandable. The system of naming leaves acropetally along the culm can easily be extended to other vegetative organs. If the unique identity of nodes, internodes, or leaf sheaths and blades is needed, they can be named in the same manner. This system was developed to identify the major above ground vegetative structures of small grains and forage grasses. Klepper et aI. (1984) expanded the scheme to include roots. The system, as presented by Klepper et al. (1983a), has been used widely by scientists to communicate the precise vegetative organ under discussion or study (Baker et al., 1986; Krenzer et al., 1991). The naming scheme is also used in models (SHOOTGRO, MODWHT) to accurately report the existence and size of organs on the simulated plants (McMaster et al., 1991; Rickrnan et al., 1996; Wilhelm et al., 1993). Allred (1982) and Allred and Columbus (1988) present concepts for delineation of grass inflorescence types and a means of applying the floral formula to grass. Klepper et al. (1983b) and Sweet et al. (1991) present numerical schemes for measuring the progression of inflorescence development. Numerous systems have been designed to assign numerical values to phenological age of culms or plants (Haun, 1973; Large, 1954; Robertson, 1968; Waldren and Flowerday, 1979; Zadoks et al., 1974). However, we know of no scheme giving unique names to reproductive structures in small grains or forage grasses. To this end, we suggest the following extension of the system described above to name uniquely reproductive structures in wheat (Triticum aestivum L .) and other grasses with spike inflorescences. The first spikelet position at the base of the rachis, whether a spikelet is developed or not, is named S1 (S for spikelet, 1 for the basal position), the second is named S2, and so on up the spike (Fig. 1). Florets (F) are designated acropetally from the base of the rachilla. The first floret is F1, the second is F2, and so forth. Abbreviations: F, floret; C, caryopsis; MS, main stem; S, spikelet; T,