The influence of plant density on flower, fruit, and leaf demography in bush bean, Phaseolus vulgaris
The influence of plant population density on bush beans is analyzed in terms of its effect on flower, fruit, and leaf demography, biomass, and yield. Plants grown at the lowest density (solitary plants) did best in terms of leaf production, total leaf days, flowers, and production of marketable pods (i.e., having at least one seed). These plants also accumulated more biomass and had greater numbers of all components of yield. In addition, they showed greater proportionate allocation to reproduction. In all density treatments the second flower cohort (produced 33–35 days after seeds were sown) made the greatest contribution to yield (43–78%). When flower production began, the rate of leaf initiation declined; leaf mortality seemed coupled to the onset of fruit production and was most severe in plants that had many pods to mature. The probability that flowers produced under any density regime would become pods and that these pods in turn would become marketable pods was assessed. Pod production was broken down into two stages: the transition from flower to fruit and from fruit to marketable pod. The results suggest that the transition from flower to fruit is not resource-limited, but the transition from fruit to marketable pod is dependent on current resource supply. When the data are examined on a per pot basis, plants at the highest density were most productive in terms of nonproductive tissues. However, an intermediate density (equivalent to 200 plants/m2) produced the greatest total reproductive biomass and the greatest number of marketable pods per unit area. The value of leaf and flower demography as measures of uniformity of maturation, optimal planting density, and cultivar performance is discussed. Key words: density, flower demography, fruit demography, leaf demography, Phaseolus vulgaris, yield.