Although growth forms in peach such as dwarf, pillar, weeping, and compact have been studied (Scorza et al., 2006), little effort has been devoted to the study of tree architecture and branching. The standard peach tree has vigorous acropetal growth, moderately strong apical dominance, and 1-year-old fruiting shoots, requiring fair to intensive pruning (Marini and Corelli-Grappadelli, 2006). There is additional genetic diversity for tree structure in closely related Prunus species that could be used to modify the architecture of peach trees (Scorza and Okie, 1990). For instance, the root-knot nematode-resistant rootstock ‘Flordaguard’, which has remarkably long pendulous branches, is a sixth-generation descendant from a hybrid between peach and the related species P. davidiana C-26712 that was subsequently backcrossed to peach (Sherman et al., 1991).
P. kansuensis ‘A1’ trees grown in Byron, GA, are short-stature and highly branched trees. Peach × P. kansuensis hybrids are vigorous and intermediate in characteristics with a higher production of lateral branches than standard peach trees (Grassell, 1974).
Almond develops lateral branches similar to peach and perennial spurs (Gradziel, 2002), although a great diversity of tree architecture can be found in this species (Kester and Gradziel, 1990). Gradziel et al. (2002) developed a classification system for branch architecture in almond based on the suppression of lateral shoot development using data from both previous and current-year growth flushes. ‘Tardy Nonpareil’ almond was categorized as having limited branching in current and previous season growth, meaning that laterals developed only on the basal half to two-thirds of the shoot. In addition, most hybrids of this cultivar tended to express this growth habit, showing that it is heritable and has a propensity toward dominance of this trait. Analysis of peach × almond F1s backcrossed to almond indicated that tree size was larger than peach and the bearing habit was similar to peach but with some prevalence of fruiting spurs (Gradziel, 2002).
For apricot there is an influence from the genotype in sylleptic branching for three locations. This influence was greater when considering cumulative effects after 3 years of growth (Legave et al., 2006). In 1-year-old progeny, high broad sense heritability was found to be 0.54 for number of axillary shoots (Segura et al., 2006, 2007).
The occurrence of blind nodes is an additional factor affecting peach tree architecture and productivity. A blind node is defined as a node lacking axillary flower and/or vegetative buds (Boonprakob et al., 1996). Blind nodes can make the training of young trees difficult and decrease potential yields in areas prone to late frosts where the crop depends on higher flower bud density to escape from poor fruit set (Richards et al., 1994).
Differences in blind node frequency among cultivars and locations can have a large impact on the pruning and potential yield in peach (Wert et al., 2007). A wide range of blind node frequency (0% to 90%) has been reported for the University of Florida peach germplasm, demonstrating that there is genetic variability for blind node incidence, and breeding against this disorder should be feasible if its mode of inheritance can be determined (Richards et al., 1994).
Blind node incidence is associated with high temperatures during bud development in the midsummer (Boonprakob and Byrne, 2003; Richards et al., 1994). Fruit of low-chill peach typically ripen before summer and the subsequent vegetative growing conditions are conducive to rapid growth and high blind node frequency (Byrne et al., 2000).
Higher rates of blind nodes are observed in warmer sites like central and southwest Florida than in north–central Florida (Wert et al., 2007). Trees grown in the highlands of the subtropics or coastal climates that have cool summers do not show blind nodes but when taken to warm humid climates such as Florida often exhibit this disorder (Richards et al., 1994). Additionally, susceptible varieties do not present blind nodes in locations with hot dry summers like Sevilla, Spain, or Hermosillo, Mexico, where climatic conditions inhibit vegetative growth during the summer (Byrne et al., 2000).
Boonprakob et al. (1996) studied anatomical differences between normal and blind nodes in ‘Earligrande’ and ‘June Gold’ peach in the spring (March, April, and May) and summer (June, July, and August). Early-season shoots presented well-developed buds with the procambium connected to the stem and prophyll growth. Late-season shoots presented mostly blind nodes and anatomical observations showed that there were empty axils with partial development of stem procambium to the position of the aborted axillary buds. In some cases, an axillary meristem was observed but with very limited growth.
Little is known about the genetics and inheritance of this phenotype for peach, although previous research indicates that highly branched Prunus kansuensis and reduced branching ‘Tardy Nonpareil’ almond will transmit these features to their respective progenies (Carrillo-Mendoza et al., 2010). In this research we are testing that the phenotypic variation for branching and blind nodes is under genetic control.
The objective of this research was to evaluate the branching intensity and blind node incidence and determine their inheritance in interspecific Prunus backcross families.
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