title: A candidate gene based approach validates Md-PG1 as the main responsible for a QTL impacting fruit texture in apple (Malus x domestica Borkh).
abstract: BACKGROUND
  Apple is a widely cultivated fruit crop for its quality properties and extended storability. Among the several quality factors, texture is the most important and appreciated, and within the apple variety panorama the cortex texture shows a broad range of variability. Anatomically these variations depend on degradation events occurring in both fruit primary cell wall and middle lamella. This physiological process is regulated by an enzymatic network generally encoded by large gene families, among which polygalacturonase is devoted to the depolymerization of pectin. In apple, Md-PG1, a key gene belonging to the polygalacturonase gene family, was mapped on chromosome 10 and co-localized within the statistical interval of a major hot spot QTL associated to several fruit texture sub-phenotypes.
  
  
  RESULTS
  In this work, a QTL corresponding to the position of Md-PG1 was validated and new functional alleles associated to the fruit texture properties in 77 apple cultivars were discovered. 38 SNPs genotyped by gene full length resequencing and 2 SSR markers ad hoc targeted in the gene metacontig were employed. Out of this SNP set, eleven were used to define three significant haplotypes statistically associated to several texture components. The impact of Md-PG1 in the fruit cell wall disassembly was further confirmed by the cortex structure electron microscope scanning in two apple varieties characterized by opposite texture performance, such as 'Golden Delicious' and 'Granny Smith'.
  
  
  CONCLUSIONS
  The results here presented step forward into the genetic dissection of fruit texture in apple. This new set of haplotypes, and microsatellite alleles, can represent a valuable toolbox for a more efficient parental selection as well as the identification of new apple accessions distinguished by superior fruit quality features.
authors.affiliation: Research and Innovation Centre, Foundation Edmund Mach, Via Mach 1, 38010, San Michele all'Adige, TN, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Longhi
authors.forename: Martha T
authors.initials: MT
authors.lastname: Hamblin
authors.forename: Livio
authors.initials: L
authors.lastname: Trainotti
authors.forename: Cameron P
authors.initials: CP
authors.lastname: Peace
authors.forename: Riccardo
authors.initials: R
authors.lastname: Velasco
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Costa
mesh_terms: D005638:Fruit / Q000235:genetics*; D006239:Haplotypes / Q000235:genetics; D027845:Malus / Q000235:genetics*; D018895:Microsatellite Repeats / Q000235:genetics; D040641:Quantitative Trait Loci / Q000235:genetics*