Effects of fruit load on flower bud initiation and development in peach

Summary

This study aims to quantify the effects of fruit crop-load on flowering and to determine the relationships between flowering and phloem sap carbohydrate and nitrogen content fractions from budding to dormancy in ‘Zincal 5’ nectarine. Fruit load significantly reduced the number of flowers per tree both indirectly, by reducing the number of shoots per tree and the number of nodes per shoot, and directly, by reducing the number of floral buds per node. The intensity of the response depended on the number of fruits developed per tree. Trees that kept all fruits up to senescence flowered 35% less than trees thinned by hand to 40% of fruits at pit hardening, and 55% less than trees completely thinned in bloom by hand. Trees that kept all fruits had significantly lower glucose and sorbitol contents in the phloem sap of mixed branches up to harvest date and full vegetative growth, respectively, but no significant relationships were found between the concentrations of these carbohydrates and flowering intensity in the following Spring. Sucrose and fructose did not show any significant difference in regard to crop-load. In fibrous roots, starch content was not related to fruit load up to dormancy, indicating that starch content is not associated with flower bud induction and differentiation. The nitrate-nitrogen fraction was significantly higher, and the ammonium-nitrogen fraction was significantly lower, in trees that tended to flower less, suggesting some disturbance in nitrate reduction in these trees.