Export yield of kiwifruit is mainly determined by fruit appearance, numbers and size, which are controlled by a number of factors.These include nutrition, pollination, water supply, and crop load, as well as such physiological factors as seed weight, flower quality and carbohydrate supply.The interaction of these factors has been studied in order to allow better control of fruit growth, and to maximise fruit size at heavy crop loads.
Individual vines of the same cultivar vary in their fruiting performance.Within a commercial orchard vines have been identified that consistently produced larger fruit than adjacent vines with a similar fruit load.Such superior vines also had good cane replacement, and heavy flowering the following year.These results may indicate an effect of rootstock selection on vine cropping.
The seed content of kiwifruit is important for fruit shape and growth, but the relationship between seed number and fruit size is complex, and varies between vines.Seed dry weight correlated better with fruit weight, than did seed number.Seed size varied for example with seed number, shading and flowering date, and such effects may account for the differences in the form of the relationship.In some vines, fruits that were small for their seed complement, had a lower mean seed weight, and mean seed weight was high in those fruits that were especially large for their seed number.Shaded fruits are smaller and contain smaller seeds, which may make them a poorer source of growth regulators and a weaker sink.Expansion of kiwifruit has been stimulated by growth regulators, and growth of fruit callus has been stimulated by growth regulators only in the presence of seeds.This may suggest a requirement for an unknown seed-factor for fruit growth, and some seeds may be more effective sources of such stimulatory substances.
Flower quality varies, and those that open earlier have a larger ovary and set larger seeds leading to larger fruits.This may be as a consequence of either their innate superiority, or their better position on the vine.Studies with 14CO2 demonstrated the influence of fruit location and seed content on assimilate distribution.The type of shoot, the age of the vine, and orthostichy also affected assimilate movement in a shoot, which has implications for control of fruit growth.In some situations high leaf numbers were found to actually reduce fruit growth independently of a direct competition effect.
