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

The shape and regularity of bell pepper (Capsicum annuum L.) fruit are know n to be determined at a very early stage of flower development. Small, flat tened fruit which are commonly parthenocarpic develop under low-temperature s (below 16 degrees 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 w inter season. In the present study it was found that deformations of flower s, similar to those found under low temperatures, were induced in 15 d by c omplete removal of fruit from plants growing under night-time temperatures of 18 degrees C. Only flowers which were at the pre-anthesis stage at the l ime of fruit removal were deformed by this treatment. Removal of leaves fro m 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 morpho logy. 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 degre es C contained more carbohydrate than those which grew at 18 degrees C. The se results suggest that flower morphology in pepper is at least partly cont rolled by source-sink relationships. Assimilates which are normally transfe rred to developing fruit may be transported, upon fruit removal, to the flo wer buds which subsequently swell. A similar increase in assimilate translo cation to flower buds may occur under low temperatures, subsequently causin g deformation of fruit. (C) 1999 Annals of Botany Company.