Adaptability, stability and leaf anatomy analysis for apple tree selection in subtropical regions

Abstract

The apple tree (Malus domestica Borkh.) belonging to the Rosaceae family. It is a fructiferous from temperate climate with exigency of cold hours varying from 100 to 2000 hours. When introduced in other climatic regions different from its origin, modifies its behavior in overcoming endo-numbness, phenology, vegetative structures and production. Apple trees breeding programs in Brazil have developed some cultivars with low demand in cold hours which has allowed the cultivation expansion of this crop to subtropical regions. In addition, environmental stresses, such as water, can be an obstacle to the correct crop exploitation in these new regions. In this context, the objective in this study was to evaluate the adaptability and stability of apple cultivars with low cold needs in a subtropical climate, as well as to perform anatomical studies of apple cultivars leaves submitted to water stress and also to shading. There were realized 3 experiments: in the first experiment, the objective was to evaluate the adaptability and stability of apple cultivars production introduced in a subtropical climate region in Brazil, adopting an univariate approach and a selection index. The adoption of a selection index provided greater confidence for the selection of apple cultivars for subtropical regions. The cultivars ‘Eva’ and ‘Julieta’ were the ones that presented greater adaptability and stability of production for subtropical regions. The second experiment consisted in comparing the leaf anatomical characteristics of apple trees in two distinct environments (drough and rainy) under tropical conditions by means of qualitative and quantitative studies of these anatomical characteristics. Apple trees leaves have anatomical characteristics that can propitiate the fruit tree productions, in places with water deficit, in subtropical regions. Although there is genetic divergence between the apple tree cultivars studied, regarding to anatomical characteristics, the cultivars ‘Gala Real’ ‘Eva’ and ‘Baronesa’ present anatomical morphological characteristics with potential of adaptation in places with water deficit. And the third experiment had as an objective to evaluate the shading effect, using photoconverting mesh of different colors, on the leaf anatomy characteristics in apple tree plants from the 'Honeycrisp' cultivar, and for this, were collected from leaves of this cultivar, which were developed under three colorations of screens (Blue, Red and White (pearl), in addition to the leaves that developed in the open sky. The different photoconverting mesh colors modify some characteristics of apple tree leaf anatomy from the ‘Honeycrisp’ cultivar. The blue color mesh provides a larger area of xylem, larger diameter of xylem vessels and greater stomatal density. The red color photoconverting mesh provides a greater number of xylem vessels. The white (pearl) color mesh provides better stomatal functionality and greater phloem thickness.