Objective 1. Create hybrid rootstocks which combine germplasm from parental material with good rootstock traits and HLB tolerance, propagate the most promising of these hybrids, and establish replicated field trials with commercial scions. During this time period, hybrid seed from 2018 rootstock crosses were planted, including SuperSour type parentage of unique HLB tolerant types. One new rootstock trial with Star Ruby grapefruit was field planted in the East coast region in April, using a replicated randomized experimental design, and included several advanced hybrid rootstocks that have demonstrated outstanding field performance in other trials, along with several commercial standard rootstocks for comparison.Multiple trees of about 150 selected new rootstock hybrids were budded and grown in the nursery, in preparation for field planting other new rootstock field trials later in 2019. These nursery trees included many of the most promising SuperSour hybrids identified in ongoing trials established in previous years, as well as several commercial standard rootstocks. These nursery trees also include other new and different hybrids chosen because of newly available information about parentage and characteristics best associated with outstanding traits. Three new field trials with sweet orange scion will be planted from these trees in 2019, including one trial in the East coast region, one in the Central ridge region, and one in the Southwest region.Objective 2. Collect field performance data from early-stage replicated rootstock field trials and release new rootstock cultivars as justified by superior performance in multiyear field trials. Seventeen rootstock trials planted prior to summer 2018 (as described in the Proposal Appendix ii) were monitored and used for data collection on field performance, as appropriate during this quarter for the scion involved. Yield and fruit quality data were collected from multiple Valencia rootstock trials, including cooperative trials with Larry Black in Polk County and Duda in Hendry County. Fruit yield, fruit quality, tree size, and other metrics from the USDA cooperative Valencia trial in Polk County were summarized in a four page handout that was distributed at the CRDF Rootstock Field Day on April 25, 2019. Three SuperSour rootstocks identified in the trials as particularly outstanding in potential yield per acre and yield efficiency are US-2122, US-2101, and US-2134, and these rootstocks will be established in additional trials and examined more carefully for potential upcoming commercial release. Seed trees of all the most promising new SuperSour hybrid rootstocks have been planted at the USDA research farm in Ft. Pierce and the Whitmore Farm to facilitate availability of seed for new rootstocks at the time of release.The three new USDA rootstocks released in November 2018, identified as US SuperSour 1 (SS1), US SuperSour 2 (SS2), and US SuperSour 3 (SS3), are being propagated in nurseries for numerous planned commercial plantings. An informational sheet with performance data on the three rootstocks was prepared and distributed widely to industry.