Create new candidate hybrids. Emphasis of hybridization in the USDA rootstock program is among parents with superior tolerance to HLB, CTV, and Phytophthora, and outstanding influence on fruit yield and quality. Some of the best performing of the newest hybrids in the Stage 1 field trials are hybrids of US-942 and US-802, so additional hybrids with this parentage are being selected for further testing. Seedlings from these crosses are being grown-out in the greenhouse in preparation for propagation, testing, and establishment of seed trees. Propagate and plant new field trials. Budwood increase trees of selected scions were grown, in preparation for budding trees for new rootstock trials. Nursery trees for Stage 1 with Valencia orange, and Stage 2 rootstock trials with Valencia, Hamlin, and Star Ruby grapefruit are being prepared in the greenhouse for field planting in 2021. Some planned propagation for new trials was delayed because of institutional Coronavirus shutdown. Collect data from field trials. 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 data on yield and fruit quality from six replicated trials with Hamlin scion. Early fruit drop data was also collected from Valencia scion trials. Assessments of tree health and measurements of tree size were completed on 10 trials during this quarter, which was reduced from the normal because of the institutional Coronavirus shutdown. Progress continued in working through the backlog of brix, acid, and color for the fruit quality analysis of last season fruit quality assessments caused by institutional Coronavirus restrictions.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 testing, seed sources are established and used to determine trueness-to-type from seed. Studies were continued this quarter to evaluate seed propagation for 25 of the most promising SuperSour hybrid rootstocks. SSR analysis of progeny is progressing more slowly than planned because of institutional Coronavirus shutdown and restrictions. Cooperative work continues to compare field performance of rootstocks propagated by seed, cuttings, and tissue culture.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/.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. Several of the 350 advanced Supersour rootstock hybrids in field trials are exhibiting outstanding performance in comparison with the commercial standard rootstocks. Performance data continues to be collected, but it is anticipated that 2-3 of the most outstanding of these will be officially released in 2021-22.