HEAT-UNIT-BASED DESCRIPTION OF THE REPRODUCTIVE DEVELOPMENT OF PEA

Yield of pea (Pisum sativum L.) is strongly dependent on two yield com ponents, seed number and individual seed mass, that depend on the sequ ential processes of reproductive development. In order to describe the reproductive development of pea, the progressions along the main stem of three stages of development-flowering, initiation of seed filling, and physiological maturity-were studied with three cultivars grown in different conditions. It was shown that the progressive development c an be described by linear functions based on cumulative degree days (C DD), using the average between daily minimum and maximum temperatures and a base temperature of 0-degrees-C. The rates of progression of flo wering (R(F)) did not vary significantly in the most favorable growth conditions for individual plants, i.e., at low plant density. The rate of progression of the initiation of seed filling (R(S)) was not signi ficantly different from that of R(F). The time interval between the in itiation of flowering and seed filling was also stable, for a given cu ltivar, but the time of physiological maturity varied widely and progr essed faster than the other stages along the stem. At high plant densi ties, when competition between plants increased, R(F) and R(S) decreas ed, but as at low plant densities, both values were not significantly different. The time interval between initiation of flowering and seed filling remained stable. In order to assess the influence of plant den sity on development, R(F) was related, the growth rate of the shoot du ring flowering (GR). The relationship showed that R(F) increased with GR until a threshold of GR. Above this threshold, which was similar fo r cultivars Solara and Frisson, R(F) remained constant. This asymptoti c value, R(F)max, differed between genotypes. If R(F)max is known, a s imple method is proposed to precisely estimate the periods of formatio n of yield components, seed number and individual seed mass, on a plan t or even a node basis. Only three simple measurements-the time of ini tiation of flowering, time to maturity, and number of highest fruiting node at harvest-are required for this calculation.