Create new candidate hybrids. Crosses were made this spring flowering season, based on parental combinations yielding the best progeny in previous trials. Hybrids from previous crosses were selected and propagated this quarter. New seed source trees for advanced selections were field planting in Spring 2022.Propagate and plant new field trials. One new Stage 2 field trial with Hamlin with selected released rootstocks and the best of the next generation hybrids was field planted this quarter. Nursery trees for one new Valencia Stage 1 trial with 60 new rootstocks that is planned for field planting in 2022 with a cooperator was delayed to finish the required MTA, and will be planted next quarter. Budwood increase trees were grown in preparation for budding trees for new rootstock trials. Trees with Valencia scion and HLB-tolerant microcitrus interstocks were planted into a field trial as a preliminary analysis of interstock feasibility.Collect data from field trials. Measurements of fruit crop and fruit quality data were collected from 9 rootstock trials with Valencia scions. The USDA researcher assisting with the analysis of fruit quality from USDA rootstock trials retired in December, so responsibility for this aspect of the work shifted entirely onto the Bowman program. Because of the Bowman program emphasis on rootstock trials, it is anticipated that this change will allow for an increase in the pace of fruit quality analysis associated with the rootstock trials. Evaluate effectiveness for seed propagation of new rootstocks and develop seed sources. As the best rootstocks are identified through field trials, seed sources are established. Studies continued to evaluate seed propagation for the most promising SuperSour hybrid rootstocks, using morphological and SSR analyses of seedling progeny for trueness-to-type. Additional effort was initiated on evaluation of seed propagation for the SuperSour rootstocks as a UF graduate student project. Field trial results for grower access. The USDA rootstock trials produce large amounts of information that is useful to help growers make informed decisions about rootstock choice for new plantings. A manuscript has been prepared that has a detailed comparison of field performance for Valencia on 50 SuperSour rootstocks and other commercial rootstocks, and this has been provided for review to selected citrus growers. It is expected that this manuscript will be submitted for publication in the coming quarter, and key findings distributed broadly to citrus growers. During this quarter, updated trial summaries from the 2021-2 season were prepared for uploading to the USDA citrus rootstock program website https://www.citrusrootstocks.org/, and information was provided to individual growers and groups, as requested.Release of superior new rootstocks for commercial use. Release of new USDA rootstocks is based on robust data from multiple trees in replicated field trials over multiple years. Several of the SuperSour rootstock hybrids in the Valencia field trial being prepared for publication have exhibited superior performance in comparison with commercial standard rootstocks and have supporting superior performance from one or more other trials. Performance data continues to be evaluated, and is being used to critically compare the new hybrids with each other and existing rootstocks. It is anticipated that 2-3 of the most outstanding of the new rootstocks from this set of SuperSour hybrids will be proposed for release in late 2022.