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.
Boonprakob, U., Byrne, D.H. & Mueller, D.M.J. 1996 Anatomical differences of axillary bud development in blind nodes and normal nodes in peach HortScience 31 798 801
Byrne, D.H., Sherman, W.B. & Bacon, T.A. 2000 Stone fruit breeding genetic pool and its exploitation for growing under warm winter conditions, p. 157–230. In: Erez, A. (ed.). Temperate fruit crops in warm climates. Kluwer Academic Publishers, Dordrecht, The Netherlands
Carrillo-Mendoza, O., Sherman, W.B. & Chaparro, J.X. 2010 Development of a branching index for evaluation of peach seedlings using interspecific hybrids HortScience 45 852 856
Doyle, J.J. 1991 DNA protocols for plants. CABI, New York, NY
Gradziel, T.M. 2002 Almond species as sources of new genes for peach improvement. Proc. of the 5th International Peach Symposium. 1:81-88
Gradziel, T.M., Kester, D.E. & Martinez-Gomez, P. 2002 A development based classification for branch architecture in almond Journal American Pomological Society 56 106 112
Grassell, C. 1974 Study of possibilities of producing intraoperative and interspecific F1-hybrids in sub-genus amygdalus Annales de Amelioration des Plantes 24 307 315
Legave, J.M., Segura, V., Fournier, D. & Costes, E. 2006 The effect of genotype, location and their interaction on early growth and branching in apricot trees J. Hort. Sci. Biotechnol. 81 189 198
Liebhard, R., Kellerhals, M., Pfammatter, W., Jertmini, M. & Gessler, C. 2003 Mapping quantitative physiological traits in apple (Malus domestica Borkh.) Plant Mol. Biol. 52 511 526
Richards, G.D., Porter, G.W., Rodriguez, J. & Sherman, W.B. 1994 Incidence of blind nodes in low-chill peach and nectarine germplasm Fruit Varieties Journal 48 199 202
Scorza, R., Miller, S., Glenn, D.M., Okie, W.R. & Tworkoski, T. 2006 Developing peach cultivars with novel tree growth habits. Proc. of the VIth International Peach Symposium. p. 61–64
Segura, V., Cilas, C., Laurens, F. & Costes, E. 2006 Phenotyping progenies for complex architectural traits: A strategy for 1-year-old apple trees (Malus × domestica Borkh.) Tree Genet. Genomes 2 140 151
Segura, V., Denance, C., Durel, C.E. & Costes, E. 2007 Wide range QTL analysis for complex architectural traits in a 1-year-old apple progeny Genome 50 159 171
Wert, T.W., Williamson, J.G., Chaparro, J.X. & Miller, E.P. 2007 Node type development of four low-chill peach cultivars at three locations in Florida HortScience 42 1592 1595