VEGETATIVE AND REPRODUCTIVE DEVELOPMENT OF STRAWBERRY GUAVA IN RELATION TO CARBOHYDRATE STATUS OF THE TREE

Abstract

Nitrogen triggers production cycle in strawberry guava (Psidium cattleianum), and numbers of shoots and flowers produced seem to depend on carbohydrate availability at the time of nitrogen application. To investigate this relationship, studies were made on the effect of two factors on the vegetative and reproductive characteristics of a triggered production cycle: the leaf-to-fruit ratio at the tree level and the fruit load at the shoot level during the previous production cycle. Leaf-to-fruit ratio was adjusted at 0.8, 2.6 and 13.2 on three trees per treatment. Three modalities of fruit load at the shoot level were considered: no fruit, 1-3 fruit(s) and >3 fruits. Nitrogen was applied about one month after full bloom of the previous cycle. At that time, starch content was determined in the leaves and wood of terminal shoots. After fruit set of the triggered cycle, leaf-to-fruit ratio of each tree was adjusted at 6.0. Numbers of shoots and flowers, and fruit set rate were recorded on the triggered cycle. Harvest data were recorded during both production cycles. Numbers of shoots and flower buds of the triggered cycle were positively correlated with starch content in leaves. However, each factor had a specific effect on vegetative and reproductive development. The number of shoots produced was negatively related to fruit load at the shoot level during the previous cycle. The number of flowers per new shoot was related to the leaf-to-fruit ratio at the tree level during the previous cycle. Any of both factors affected fruit set rate. Carbohydrate availability at the time of nitrogen application had therefore a positive effect on flower induction, and growing fruits seemed to prevent vegetative development. Fruit growth was sensitive to carbohydrate supply. (Resume d'auteur)