The 2011 ASHS Annual Conference

As labor and pruning costs of fruit trees have increased, the importance of size control and tree architecture has gained importance. Tree architecture will continue to increase in importance as a major trait for tree fruit breeders. Numerous growth forms have been described in peach including, dwarf, compact, weeping, and pillar, however, little effort has been made to understand the genetic control of tree architecture in peach. Traits that determine the complexity of peach tree structure in subtropical climates include the frequency of nodes without floral and vegetative buds (blind nodes) and the propensity of vegetative nodes to grow and elongate.   Seven backcross families were generated to study the inheritance of these traits in peach.  The species Prunus kansuensis Rehder (Kansu peach), P. dulcis (Mill.) D.A. Webb (almond) and P. persica (L.) Batsch (peach).  were used to generate the study populations.  The three species differ in their growth habits and blind node incidence.  Kansu peach, a wild peach relative, has a dense canopy with profuse branching. In contrast, almond expresses a reduced branching phenotype with an open tree canopy and can produce short branches resembling spurs. Commercial peach germplasm typically has a branching architecture that is intermediate to the two described above, but exhibits both twiggy and non-twiggy phenotypes. Backcross progeny were evaluated for blind node frequency and branching propensity.  A branching index was developed to facilitate the assessment of branching intensity of the trees in the study.  Microsatellite markers from the reference linkage map of peach were used to map QTL’s associated with tree architecture and blind node incidence across the genome of the different BC families. Candidate genes affecting axillary meristem development are under study to develop markers for branching intensity and blind node incidence which will be mapped on the backcross progeny.