Create new candidate hybrids. Planning is in progress for new hybrids to be created during next quarter (Spring 2022), 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 prepared for field planting in Spring 2022.Propagate and plant new field trials. One new Stage 1 field trial with Valencia and one new Stage 2 field trial with Valencia were field planted this quarter. Trees for a Stage 2 Hamlin trial with selected released rootstocks and the best of the next generation hybrids are being grown in the greenhouse in preparation for field planting in Spring 2022. Nursery trees for one new Valencia Stage 1 trial with 60 new rootstocks are being prepared for field planting in 2022. Budwood increase trees were grown in preparation for budding trees for new rootstock trials. Trees with Valencia scion and HLB-tolerant interstocks were propagated as a preliminary analysis of interstock feasibility.Collect data from field trials. Measurements of fruit crop and fruit quality data were collected on 6 rootstock trials with Hamlin and other early season scions. The USDA researcher assisting with the analysis of fruit quality from USDA rootstock trials retired this quarter, 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. Studies continued to evaluate seed propagation for promising SuperSour hybrid rootstocks, using morphological and SSR analyses of seedling progeny for trueness-to-type. Additional effort was initiated on this subject as a graduate student project. As the best rootstocks are identified through field trials, seed sources are established. Cooperative work continues to compare field performance of rootstocks propagated by seed, cuttings, and tissue culture. Evidence indicates that performance of rootstocks is primarily determined by rootstock cultivar, with only small influences by propagation method.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 is in preparation that has a detailed comparison of field performance for Valencia on 50 SuperSour rootstocks and other commercial rootstocks, and selected excerpts from this were prepared for presentation at the 2022 Florida Citrus Show and the January 2022 meeting of the Florida Citrus Research Foundation. During this quarter, updated trial summaries 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. Assessments of trees in trials includes information on tree survival and health, canopy size, fruit yield and fruit quality, and observations on tolerance of disease and other biotic and abiotic threats. Several of the 350 advanced Supersour rootstock hybrids in field trials are exhibiting outstanding performance in comparison with commercial standard rootstocks. Performance data continues to be collected 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 SuperSour hybrids will be officially released in 2022-23.