Articles
EFFECTS OF ALTERED SOURCE-SINK RELATIONSHIPS ON FRUIT DEVELOPMENT AND QUALITY IN ACTINIDIA DELICIOSA
Two weeks after full bloom, defoliation and pruning to give leaf-to-fruit ratios of 0.75/1, 2/1 and 4/1, girdling and CPPU (20 ppm) fruit treatment were performed on fruiting laterals fully exposed to the sun, carrying 3–4 fruits each.
Fruit growth and characteristics at harvest (flesh firmness and soluble solids, dry matter, glucose, fructose, sucrose and starch contents) were not affected by the different leaf-to-fruit ratios when the fruiting shoots were not girdled.
Treatment of fruits on ungirdled laterals with CPPU caused an increase in the fresh and dry fruit weights by about 65% and 50%, respectively, irrespective of the leaf-to-fruit ratio.
When laterals were girdled, the different leaf-to-fruit ratios strongly affected fruit characteristics at harvest.
Compared to fruit on ungirdled shoots, the 4/1 ratio increased fruit growth (about + 50%), both on a fresh and dry weight basis; the 2/1 ratio gave a similar fruit growth on a fresh weight basis, but caused a reduction in dry weight; the 0.75/1 ratio strongly reduced fruit growth, both on a fresh and dry weight basis.
In general, CPPU did not cause any increase in fruit growth on girdled laterals with 2/1 and 0.75/1 ratios, whereas CPPU markedly increased fruit growth on girdled laterals with a 4/1 ratio.
The results indicate that in Actinidia deliciosa is necessary to have between 2 and 4 leaves fully exposed to the sun per fruit to ensure normal fruit development and quality and that the assimilates can be easily translocated within the plant to support fruit growth on shoots with an inadequate leaf to fruit ratio.
In addition, there is a great potential for increasing fruit size, when there is high assimilate availability and/or after an increase in sink strength, indicating the possibility for improving the qualitative traits of the crop.
Finally, the results show that the increase in sink strength and/or assimilate availability influences fruit size more than the qualitative characteristics of the fruits (carbohydrate content, flesh firmness, etc.).