Interrelationship between Meristematic Regions of Developing Inflorescences of Four Cereal Species

A cultivar from each of four cereal species (Avena sativa L., cv. Swan, Hordeum vulgare, L., cv. Clipper, Triticum aestivum L., cv. Gabo, and Secale cereale L., cv. South Australian Rye) was grown in controlled environment chambers in a 10-h photoperiod (short days) or 10-h photoperiod supplemented with a 6-h extension by incandescent light. The developmental morphology of the inflorescences was followed to ascertain whether there were any common developmental interrelationships between the species. Inflorescence internode elongation was initiated when the floret initial first appeared, irrespective of whether it occurred on the most advanced lateral spikelet or on the terminal spikelet of the rachis. The glumes (infertile bracts) of the terminal spikelet of the rachis were initiated when the first second-order inflorescence branch appeared, irrespective of whether the second-order inflorescence branch was a floret initial or a lateral spikelet, as in Triticum sp., or an inflorescence (panicle) branch, as in Avena sp. Cessation of the activity of the apical meristem, as measured by primordium formation, was not correlated with any particular stage of floral development but appeared to be due to a lack of nutrients caused by an increasing competitiveness for the available nutrients from the developing spikelets which are situated closer to the vascular system than the apical meristem.