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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Insects and Horticulture Research » Research » Publications at this Location » Publication #386804
Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Huanglongbing Disease and Other Stresses

Location: Subtropical Insects and Horticulture Research

Title: SuperSour: A new strategy for breeding superior citrus rootstocks

Author
item Bowman, Kim
item McCollum, Thomas
item ALBRECHT, UTE - University Of Florida

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2021
Publication Date: 11/4/2021
Citation: Bowman, K.D., Mccollum, T.G., Albrecht, U. 2021. SuperSour: A new strategy for breeding superior citrus rootstocks. Frontiers in Plant Science. 12, 741009. https://doi.org/10.3389/fpls.2021.741009.
DOI: https://doi.org/10.3389/fpls.2021.741009

Interpretive Summary: Citrus crops are primarily grown as grafted trees on rootstock varieties. The choice of rootstock has a large effect on tree survival and size, as well as fruit production and fruit quality. Diseases such as huanglongbing severely damage the production of citrus, and can be ameliorated by using tolerant rootstocks. Although some existing rootstocks are much better than others, all current rootstock have flaws or limitations,and improved new rootstocks are urgently needed to support continued profitability of production and continued availability of citrus fruit and products in the market. Traditional methods of citrus rootstock breeding take at least 2-3 decades to develop and test new hybrid rootstocks. We describe a new citrus rootstock breeding strategy implemented by the USDA, that dramatically shortens the time to develop a new citrus rootstock,and increases the potential for significantly better rootstocks. The new SuperSour strategy has several key features, including the use of different methods for propagation, numerous coordinated and replicated field trials, and a broader germplasm base. Multi-year yield, tree health, and fruit quality information is presented from two of the SuperSour trials to illustrate the strategy and potential for significant improvements in rootstock performance.

Technical Abstract: Citrus crops have a long history of cultivation as grafted trees on selected rootstock cultivars, but all current rootstocks have significant limitations and traditional methods of rootstock breeding take at least 2-3 decades to develop and field test new rootstocks. Citrus production in the US, and other parts of the world, is impaired by a wide range of biotic and abiotic problems, with especially severe damage caused by the disease huanglongbing (HLB) associated with Candidatus Liberibacter asiaticus. All major commercial citrus scion cultivars are damaged by HLB, but tree tolerance is significantly improved by some rootstocks. To overcome these challenges, the USDA citrus breeding program has implemented a multi-pronged strategy for rootstock breeding that expands the diversity of germplasm utilized in rootstock breeding, significantly increases the number of new hybrids evaluated concurrently, and greatly reduces the time from cross to potential cultivar release. We describe the key components and methodologies of this new strategy, termed “SuperSour”, along with reference to the historical favorite rootstock sour orange (C. aurantium), and previous methods employed in citrus rootstock breeding. Rootstock propagation by cuttings and tissue culture is one key to the new strategy, and by avoiding the need for nucellar seeds, eliminates the 6-15-year delay in testing while waiting for new hybrids to fruit. In addition, avoiding selection of parents and progeny based on nucellar polyembryony vastly expands the potential genepool for use in rootstock improvement. Fifteen new field trials with more than 350 new hybrid rootstocks have been established under the SuperSour strategy in the last eight years. Detailed multi-year performance data from the trials will be used to identify superior rootstocks for commercial release, and to map important traits and develop molecular markers for the next generation of rootstock development. Results from two of these multiyear replicated field trials with sweet orange scion are presented to illustrate performance of 97 new hybrid rootstocks relative to four commercial rootstocks. Through the first 7 years in the field with endemic HLB, many of the new SuperSour hybrid rootstocks exhibit greatly superior fruit yield, yield efficiency, canopy health, and fruit quality, as compared with the standard rootstocks included in the trials.