| Abstract: | Reproductive development in cereals is not easy to investigatebecause their quantitative response to environmental factorsmakes it difficult to synchronize the plants. In this paper,one of our aims was to assess whether Lolium temulentum strainCeres, a qualitative long-day grass, could serve as a modelof reproductive development for cereals. The morphological patternsfrom floral transition to seed set were studied. A flowering scale was established to evaluate developmentalrate during spike morphogenesis. Apex growth was found to increaseaccording to biphasic kinetics; double ridge appearance markedthe beginning of an exponential phase. Developmental progression and apical growth rate were both increasedby giving repeated long days. In contrast, the final numberof lateral spikelets (20–25) could not be manipulatedafter the beginning of long-day treatment. When plants were kept in continuous light from the beginningof induction, double ridges appeared on the fifth 24 h cycle.Spikelet initiation began in the upper mid-part of the spike,and then extended acro- and basipetally. The phase of spikeletinitiation lasted 6 d, with l?5 to 1?9 spikelets being produceddaily. Within each spikelet, florets were initiated at an averagerate of l?3 primordia per day and developed acropetally. Thefirst signs of apical site degeneration were observed in themost developed upper spikelets just before heading. Ear emergenceoccurred between the 20th and 25th cycles of continuous light;anthesis was observed 6 or 7 d later. The proportion of floretssetting grain averaged about 40%. Grains were produced mainlyin the lower spikelets while the upper mid-part of the inflorescenceshowed a much lower fertility rate. Complex developmental gradients described in this paper suggestthat L. temulentum could serve as a model of reproductive developmentin cereals, with the added advantage of flowering in responseto a single long-day. Key words: Lolium temulentum L., spike morphogenesis, spikelet number, floret number, grain set |
