Within-bunch variability in banana fruit weight:: Importance of developmental lag between fruits

Within-bunch (inflorescence) variability in banana fruit weight is of great importance: distal fruits (at the bottom of the bunch) are 30 to 40 % smaller than basal fruits at the top. We hypothesize that this variability is related to a developmental lag between fruits. To validate this hypothesis, histological studies (evolution in number of cells along the fruit radius, starch granule number and size) associated with physiological measurements (pulp dry weight, dry matter and starch concentration) were carried out. Fruit development stages were dated in cumulative degree-days (dd) from flower emergence to 3 weeks after the harvest stage (1300 dd). For a fruit located at the top of the bunch, cell divisions ceased around 350 dd and cells began to fill with starch as soon as they appeared. A developmental lag between fruits at the top and bottom of the bunch was observed: cell divisions started and stopped approx. 70 dd later in bottom (distal) compared to top (basal) fruits. At the end of cell divisions, basal fruits had a higher number of cells along the fruit radius. This difference in cell number may be due to increased competition for assimilates between fruits when cell division occurs in distal fruits. Variability in cell number may be related to variability in pulp dry weight. We conclude that within-bunch variability in banana fruit weight is related to a difference in cell number and age. (C) 2001 Annals of Botany Company.