Manipulação da relação fonte-dreno em Coffea arabica L. e seu efeito durante o desenvolvimento dos frutos

Abstract

Brazil is positioned as one of the largest coffee producers in the world, with 2.16 million hectares planted. Combining quality and production, it appears as the largest exporter of the grain. Biomass production is dependent on the assimilation and partition of carbon (C) in the plant. For the fruit to grow, C is required directly from the photosynthesis of the leaves, from the reserves of the branches and roots, and from assimilation by the fruit itself. The manipulation of source-sink relationships, through techniques such as girdling, defoliation and fruit removal, help to modify the carbohydrate flow, allowing to alter the carbon partition in the plant. The objective of this study was to determine the production capacity and carbohydrate storage in the branches and fruits of the coffee tree. Two experiments were conducted: In the first, the applicability of in situ estimation of the volume and area of coffee pods was evaluated with a mathematical method for an ellipsoid, creating an estimation method using a correction factor to estimate the volume and area of coffee rosettes, comparing to conventional methods. For this, 569 fruits of different development stages were evaluated and the following parameters were measured for each fruit: length (X axis), width (Z axis) and height (Y axis). The dimensions collected with a caliper were used in the equation to estimate volume and area. The morphometric dimensions of the fruits showed a high correlation with the dimensions used for an ellipsoid with three different axes, such as the coffee fruit. The efficiency of this model was evaluated by linear regression, showing in its ANOVA analysis (p<0.01) and a positive linear relationship between the two methods. The two models are said to be suitable for in situ estimation of the volume and area of fruits and coffee rosettes, without causing damage to the fruits and with an accurate and practical estimation in the field. The second experiment aimed to determine the contribution of different parts of the coffee tree as a source of carbohydrates for fruit growth and carbohydrate accumulation as a function of development stages. The variation factors were the techniques for manipulating source-sink relationships: (i) girdling of the plagiotropic branch and (ii) defoliation and their combinations. Six collections were carried out during the development of the coffee fruits to quantify the carbohydrates. There was a limitation and delay in the growth of fruits from the ringed and defoliated branches, reducing the accumulation of carbohydrates throughout development. Ringed branches and with leaf show greater activity in the metabolism and transport of carbohydrates, and this contribution minimized the impact on coffee pod growth. There is a balance in source-sink relationships where all parts of the coffee plant are connected, helping fruit growth, whose balance can be changed according to the increase in fruit demand.