The effect of fruit load, defoliation and night temperature on the morphology of pepper flowers and on fruit shape

Abstract

The shape and regularity of bell pepper (Capsicum annuum L.) fruit are known to be determined at a very early stage of flower development. Small, flattened fruit which are commonly parthenocarpic develop under low-temperatures (below 16 °C) from flowers with enlarged ovaries. In such flowers self-pollination is not efficient because of the large distance between the stigma and stamens. Flower deformation of this kind is common during the winter season. In the present study it was found that deformations of flowers, similar to those found under low temperatures, were induced in 15 d by complete removal of fruit from plants growing under night-time temperatures of 18 °C. Only flowers which were at the pre-anthesis stage at the time of fruit removal were deformed by this treatment. Removal of leaves from the lower part of the plant (source leaves) partially reduced the effect of fruit removal on the shape of the flowers and on subsequent fruit morphology. Fruit removal induced significant increases in the concentrations of starch and reducing sugars, but not sucrose, in the flower buds. Likewise, flower buds of plants which grew under a night-time temperature of 12 °C contained more carbohydrate than those which grew at 18 °C. These results suggest that flower morphology in pepper is at least partly controlled by source-sink relationships. Assimilates which are normally transferred to developing fruit may be transported, upon fruit removal, to the flower buds which subsequently swell. A similar increase in assimilate translocation to flower buds may occur under low temperatures, subsequently causing deformation of fruit.