Respostas bioquímico-fisiológicas, transcricionais e mapeamento de QTLs de frutos na pós-colheita.

Abstract

During fruit ripening, besides the changes in color, there are changes that contribute to improving the flavor, texture and nutritional and functional quality attributes. In climacteric fruits, such as tomatoes and apples, the evolution of quality attributes is influenced by the plant hormone ethylene, which is drastically increased during maturation. In order to reduce losses in fruit quality attributes, new technological strategies have been developed. Treatment with UV-C radiation, in addition to its known germicidal effect, is one of these strategies than can slow down the ripening process. In addition, UV-C acts as a stressor agent, capable of inducing defense mechanisms, that it is qualified by specialized metabolism. Thus, in the first study of this thesis (article I), we evaluated the molecular and metabolic changes resulting from the action of UV-C in stored tomatoes cv. Flavortop, and its relationship with events influenced by ethylene. For such, the following treatments were performed: UV-C 3.7 KJ/m2, 1-MCP (1-methylcyclopropene) at 2μL/L, and 1-MCP+UV-C. From these treatments it was observed that although the UV-C radiation stimulated ethylene production but delayed red color development of fruits. There was reduction of firmness independently of the treatments, but at lower intensity in fruit treated with 1-MCP. In general, there was an increase in the transcript accumulation of all studied genes one day after UV-C treatment, while 1-MCP treatment limited this accumulation. Polyamine content in fruit treated with UV-C was higher when compared to the other treatments, suggesting a possible relationship between these molecules and ripening delay. In the second study (article II) quantitative trait loci (QTLs) were identified for the main parameters of apple texture, which is a major component of consumer preference for apple quality. For this study, fruits were harvested in 2007 and 2011 at two stages of maturity, early and optimum, and evaluated at harvest and after two months of storage at 1.5 °C ± 80% relative humidity. The study samples were derived from a cross between X3259 and X3263 genotypes. The phenotyping was performed for sensory and instrumental measurements (penetrometer and compression) and histological analysis. A genetic map with 17 linkage groups was already available for this cross. A total of 19 QTLs were identified in six linkage groups (LG01, LG02, LG07, LG10, LG11 and LG16) of integrated genetic map. The percentage of phenotypic variation (R2) ranged between 8.7% and 67.6%. Some of the regions where QTLs were found are co-located with candidate genes already mapped and available in the literature. From the results obtained in both studies, it was found that: 1) the UV-C radiation acts on a molecular level, triggering different biochemical and physiological responses in fruits, especially in the production of ethylene, the retardation of color development and biosynthesis polyamines; 2) QTL mapping provides bases for finding candidate genes that control the structural determinants of texture of apple and open new perspectives for breeding programs.