Molecular markers to select apple cultivars with low ethylene production.

Resumo expandido.

English. Shelf life of a fruit is an important economic aspect even after a certain period of storage, which is influenced by the genetic constitution of the fruit. Good shelf life is associated with a slow break down of firmness of mature fruit at room temperatures (Costa et al., 2005). Excessive softening is considered undesirable in apple and can impair characteristics like firmness, juiciness, crispness of fruit, as well increase mealiness (Oraguzie et al., 2004). In climacteric fruits, like apple, fruit ripening is controlled by the internal ethylene concentration. Ethylene is a gaseous hormone in higher plants and controls the ripening of climacteric fruit by coordinating the timely activation of many genes that cause changes in color, texture, aroma and flavor (Oetiker and Yang, 1995). The hormone is synthesized from S-adenosyl-L-methionine (SAM) via a short pathway catalysed by two enzymes, both encoded by two large gene families: 1-aminocyclopropane-1-carboxylic acid (ACS) synthase and 1-aminocyclopropane-1-carboxylic acid oxidase (ACO). The conversion of SAM to ACC by ACC synthase is the first step in ethylene biosynthesis and is generally considered to be the rate-limiting step (revision in Oraguzie et al., 2004; Oraguzie et al., 2007). The difference in ethylene production rate observed among apple cultivars can be related to different allelic combinations for these genes (Zhu and Barritt, 2008). Use of marker-assisted selection in conventional apple breeding programs should significantly increase breeding efficiency since undesirable genotypes can be eliminated at the early seedling stage. Considering this scenario the aim of this study was perform a screening in apple cultivars and clones using three molecular markers to select genotypes related to low ethylene production: ACS1, ACS3a and ACO1. This screening can contribute with information for future apple breeding programs.