Genetics of tree architecture in peach (Prunus persica (L.) Batsch)

Little effort has been made to understand the genetic control of tree architecture in peach. In addition, the occurrence of blind nodes is a critical factor that affects peach tree architecture and productivity in subtropical climates. In this study, a branching index was developed to facilitate the assessment of branching intensity of the trees. Seven backcross families were developed using Flordaguard' peach x P. kansuensis or 'Tardy Nonpareil' almond F1s backcrossed to 'AP00-30wbs', 'UFSharp' or 'UF97-47' peach selections and evaluated for branching index and blind node frequency during the winters of 2010 and 2011. P. kansuensis backcrosses presented increased branching and lower blind node incidence whereas almond backcrosses presented less branching and higher blind node incidence, resembling the P. kansuensis and almond F1 parents. There was also broad variability for branching and blind nodes within the P. kansuensis and TNP almond backcross families influenced by the peach parents that were used to generate the backcross populations. The moderate heritability and year-to-year correlation for these traits indicate that they are affected by the environment, but selection for reduced branching and lower blind node incidence is feasible. SSRs and a set of 14 candidate genes related with branching and bud development in Arabidopsis were used to map QTLs associated with these two traits in the seven backcrosses. SNPs were found within the candidate gene sequences in the different Prunus parents. Genetic maps containing the selected SSRs and candidate genes were obtained for each backcross family and a combined map for all the P. kansuensis families and all the almond families. Branching and blind nodes QTL were detected in the individual backcross family analysis, and the combined P. kansuensis and 'Tardy Nonpareil' almond families analysis. The candidate genes tested did not map to the location of the major QTLs, PpCUC1 and PpBRC2 mapped to minor QTL for branching and blind nodes, respectively. The QTLs found in this study represent the first steps toward marker assisted selection for reduced branching and reduced incidence of blind nodes in commercial peach cultivars.