2018 ASHS Annual Conference

Courtney Hollender, Chinnithambi Srinivasan, Ralph Scorza, and Chris Dardick

Tree fruit production has been increasingly moving towards high density orchards. This is change is being driven by a need to increase production with limited resources, including labor. Most fruit trees, however, aren’t naturally amenable to high density growth. The use of dwarfing rootstocks has been essential for the success of high density apple plantings. However, many fruit tree species lack size-controlling and dwarfing rootstock. In addition, time consuming branch training, scoring, and growth regulator applications are also needed for high density production. This amount of labor isn’t practical for some species. Fortunately, fruit tree germplasm collections contain trees with more amenable architectures, including smaller statures and growth habits with potentially beneficial shoot orientations. Technological advances, such as high throughput sequencing, have enabled the genetic causes for these traits to be identified. Coupling this ability with improvements in tree transformation and gene editing can enable generation of newer cultivars and cultural practices that could make high density orchards a reality for more fruit species. The recent identification of genes associated with non-standard peach architectures exemplify this advancement. Mutations in the TAC1 gene were found to be the cause pillar or columnar growth habits in peach. The repression of this gene in plum led to slender pillar plums, which can be planted closer together than standard plums. In addition, the overexpression of TAC1 also resulted in plums with wide branch angles. Wide angles can cause plagiotropic growth, which is desirable for trellis-based high density systems. The identification of TAC1 also led to the identification and manipulation of a related plum gene, LAZY1. Reduction in LAZY1 expression in plum resulted in trees also produced trees wider branch angles. Other examples of the utility of gene identification and manipulation include the modulation of GID1c expression. A mutation in GID1c is the cause of dwarf peach phenotype, and reducing the expression level of this gene in plum produced dwarf and semi dwarf trees. Taken together, these results illustrate the possibility for rapidly breeding trees specific for high density stand alone and trellis-based plantings, which are needed for the tree fruit production sustainability in the future.