Partitioning of assimilates in fruiting tomato plants

Abstract

Tomato is a potentially high-yield crop with a harvest index of about 65%. During fruiting, fruit growth accounts for 80 to 90% of the plant fresh weight gain and fruits are therefore the strongest sinks for assimilate. At initiation, an inflorescence is a weak sink in comparison with apical shoots. When assimilate supply is inadequate, the inflorescence has a reduced level of endogenous cytokinin and the degree of abortion is inversely related to the activity of sucrose hydrolase. Application of cytokinin plus gibberellins to the inflorescence increases its capacity to attract assimilate at the expense of apical shoots. At fruit set, cell division is activated and the ovary starts to accumulate reducing sugars and starch. Both the final cell number and the potential cell size are determined in the first two weeks and may be related to the levels of cytokinin and auxin. At the early stage of rapid growth a fruit accumulates imported assimilates, mainly in the forms of hexoses and starch. The rate of starch accumulation increases with the absolute fruit growth rate and affects the final soluble solids content of a fruit. The change in the fruit growth rate during fruit development does not coincide with the changes in the endogenous hormone levels of the fruit. A fruit competes for assimilate with others mainly in the same truss.