Create new candidate hybrids. During this quarter, hybrids from previous cycles were selected, and propagation planned for the next cycle of Stage 1 field trials. New seed source trees were propagated for advanced selections and planted in the field. Based on new information on performance of different parental combinations in rootstock field trials, additional crosses among the best parental material are planned for next spring, as resources are available. Propagate and plant new field trials. Budwood increase trees of selected scions were grown, in preparation for budding trees for new rootstock trials. Trees for Stage 2 rootstock trials with Valencia and Hamlin on selected released rootstocks and the best of the next generation hybrids are being grown in the greenhouse in preparation for field planting in 2021. One new Stage 2 trial with Valencia scion and one new Stage 2 trial with grapefruit scion were planted in the field. Nursery trees for two new Stage 1 trials with 60 new rootstocks and Valencia were propagated in the greenhouse in preparation for field planting in fall 2021. Some planned propagation for new trials was delayed because of USDA institutional Coronavirus shutdown. Collect data from field trials. Extensive information on tree performance is collected from established field trials, and includes measurement of tree size, fruit crop, fruit quality, and pathogen titer, HLB symptoms, and assessments of tree health. Cropping data is collected during the time of scion harvest, and during this quarter none of the active trials have scions for which crop would normally be harvested. Assessments of tree health were completed on 23 trials during this quarter. All the backlog of fruit quality analysis (caused by institutional Coronavirus restrictions) from frozen juice samples in the previous season was completed, with full data on brix, acid, and color from 15 replicated trials. Because the data collection load from field trials was lower this quarter, additional effort was put into tree maintenance, and updates to irrigation and drainage systems in selected trial blocks.Evaluate effectiveness for seed propagation of new rootstocks and develop seed sources. Some of the newest hybrid rootstocks can be uniformly propagated by seed, but others cannot. As the best rootstocks are identified through field trials, seed sources are established and used to determine trueness-to-type from seed. Studies were continued this quarter to evaluate seed propagation for 20 of the most promising SuperSour hybrid rootstocks. Progeny groups were scored, and tissue samples were prepared for SSR analysis of progeny to determine frequency of nucellar polyembryony and uniformity from seed. This work is progressing more slowly than planned because of institutional Coronavirus restrictions. 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, and not much influenced by propagation method.Posting field trial results for grower access. The USDA rootstock trials produce large amounts of information that is useful to identify the most promising of the new hybrids, as well as comparative information on the relative performance of many commercially available rootstocks. During this quarter, updated trial summaries were prepared for uploading to the website https://www.citrusrootstocks.org/, and a presentation on rootstock performance in field trials was given at the Florida Grower Citrus Show.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, including 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. Outstanding performance in industry plantings from some of the previously released USDA rootstocks, especially US-942 and US-812, indicate the process is effective. Several of the 350 advanced Supersour rootstock hybrids in field trials are exhibiting outstanding performance in comparison with the commercial standard rootstocks. Information on some of the most promising of the next-generation USDA hybrid rootstocks was presented at the Florida Grower Citrus Show. Performance data continues to be collected, and it is anticipated that 2-3 of the most outstanding of these will be officially released in 2022-23.