Location: Fruit and Tree Nut Research
2019 Annual Report
Objectives
1. Develop new high-chill stone fruit cultivars for main season production areas with improved adaptability, cropping reliability, disease resistance, handling ability, and eating quality.
2. Develop new moderate-chill stone fruit cultivars for early season production areas in the lower coastal plain with improved adaptability, cropping reliability, tree architecture, disease resistance, handling ability, and eating quality.
3. Develop new stone fruit rootstocks with improved disease resistance and a range of vigor control to manage tree size.
Approach
Elite breeding lines and select varieties with appropriate traits will be hybridized and the best hybrid seedlings selected. These selections will be tested for multiple years in several locations to identify those truly superior to existing commercial varieties in terms of cropping reliability, productivity, fruit size, appearance, firmness and eating quality. These superior selections will then be named and released for use by the commercial peach industry.
Parental root-stock lines with superior resistance to peach-tree short life, Armillaria root rot and commercially important root-knot nematode species will be intercrossed to produce hybrid seedlings with the desired characteristics. Extensive field testing will be utilized to identify those hybrids which have the requisite combination of disease resistance and horticultural traits for successful commercial utilization the southeastern U.S. peach industry. Best selections will be released for commercial utilization.
Progress Report
Hybridizations were made for both peach variety development programs. Progress was made in the field with adapted varieties and breeding lines which managed to escape the late freeze. Fruit set was excellent for high-chill peach lines in the field and for the moderate-chill peach and rootstock lines in the plastic covered greenhouse. Peach seedlings generated in the 2018 pollination season were planted into the field for evaluation. Advanced variety selections nearing completion of evaluations were scaled up in anticipation of impending releases. Evaluations and selections were made in both programs.
New variety trials of recent releases from the high-chill and moderate-chill variety development program are continuing under Material Transfer/Plant Evaluation Agreements in Georgia, Alabama, and Florida to test the performance of these materials against standard commercial varieties under their climatic regime and management programs.
Hand pollinated crosses were made for the rootstock development program. New Peach Tree Short Life, Armillaria root rot, Root-knot nematode, Horticultural and Graft Compatibility trials were established at the Byron location. Previously established grower trials at other locations are continuing to be evaluated. New rootstock selections were made and propagated for further development. Advanced rootstocks selections nearing completion of evaluations were scaled up in anticipation of impending release(s).
Rootstock trials of MP-29 and advanced selections established under Material Transfer/Plant Evaluation Agreements in Georgia, Alabama, South Carolina and Texas with collaborators to test the response of these materials to local isolates of Armillaria tabescens are continuing. A trial established with a collaborator in Michigan to evaluate rootstock influence on cold hardiness of the scion variety is continuing; a new trial to assess the utility of MP-29 in high density plantings was established. Trial established in Georgia to evaluate novel management approaches to rootstock sucker suppression and response to differential fertilization and irrigation regimes are also continuing. A new trial was established with a collaborator in Texas to test the response of MP-29 and advanced selections to a local isolate of Phymatotrichum omnivorum was established and is continuing.
Accomplishments
1. Preparation and submission of patents for three new main-season peach cultivars. Peach industries in the southeastern states still need peach cultivars that have better adaptation, crop more reliably under suboptimal weather patterns, and/or fit some important harvest windows. Taken those into consideration, an ARS researcher in Byron, Georgia, approved three new peach cultivars for release and the applications for plant patents were submitted. Two of the cultivars provide improved cropping reliability and the third fills a critical gap in the harvest window.
2. Development of new primers of Xylella fastidiosa, the causal agent of phony peach disease, for improved reliability and sensitivity in both conventional and quantitative PCR detection of the pathogen. Phony peach disease is incurable, and management depends on early detection and removal of infected trees. An ARS researcher in Byron, Georgia, developed and assessed new primers of Xylella fastidiosa for both conventional and quantitative PCR detection of the pathogen with improved reliability and sensitivity. The improvement in detection and new knowledge of the titer differences among tissues from different seasons help manage the disease more efficiently.
3. A new nursery licensed to propagate MP-29 rootstock. Supported by the ARS Innovation Fund, based on a grower demo trial ARS researchers in Byron, Georgia, collaborated with an established nursery in the middle Georgia area to become licensed to propagate MP-29 rootstock. This is a significant step forward as this trial demonstrated that at this latitude marketable trees on MP-29 can be produced in a single season unlike the 2-season protocol currently being used by nurseries in Tennessee which are currently the primary suppliers of trees into the Southeastern peach industry.
4. Submission of invention disclosure for P-22 rootstock. An invention disclosure for P-22, a peach seedling rootstock, was submitted by ARS researchers in Byron, Georgia, and it was approved for patenting and release. P-22 offers significant improvements on Guardian rootstock. P-22 has red leaves which is an aid in the nursery. It is comparable to Guardian in productivity, fruit size, vigor and resistance to peach tree short life (PTSL) but improves on Guardian’s many attributes with broader and better root-knot nematode resistance while providing a useful level of resistance to Armillaria root rot (ARR), Guardian’s Achille’s heel. While not as resistant to ARR as MP-29, P-22, nevertheless, offers an advantage over MP-29 in that it fits into the typical one-year production cycle utilized by nurseries in Tennessee.
Review Publications
Chen, C., Bock, C.H., Brannen, P.M. 2019. Novel primers and sampling for PCR detection of Xylella fastidiosa in peach. Phytopathology. 109(2):307-317. https://doi.org/10.1094/PHYTO-11-18-0439-FI.
Chen, C., Bock, C.H., Brannen, P.M., Adaskaveg, J.E. 2018. Mining and characterization of microsatellites from a genome of Venturia carpophila. Mycological Progress. 17(8):885-895. https://doi.org/10.1007/s11557-018-1401-x.
Beckman, T.G., Rollins, A., Pitts, J., Chavez, D., Chaparro, J.X. 2019. Disease resistance of ‘MP-29’, a clonal interspecific hybrid rootstock for peach, in post-release trials. HortScience. 54(4):638-641. https://doi.org/10.21273/HORTSCI13592-18.
Calovic, M., Chen, C., Yu, O., Orbovic, V., Gmitter Jr, F.G., Grosser, J.W. 2019. New somatic hybrid mandarin tetraploids generated by optimized protoplast fusion and confirmed by molecular marker analysis and flow cytometry. Journal of the American Society for Horticultural Science. 144(3):151-163. https://doi.org/10.21273/JASHS04563-18.
