About 500 supersour-type (SS) rootstock hybrids have been selected for propagation and further testing. Selected SS rootstocks are being evaluated for tolerance to CTV quick decline and propagated for placement into field trials. Commercial cooperators are being identified who will host early stage trials of some SS rootstocks. Rootstock liners were budded with scions to prepare trees for trials. Budded greenhouse trees for field trials were grown to planting size. A new field trial was planted to assess the interaction of rootstocks and scion cultivars on tree performance under an open hydroponic management system. Data on tree size and HLB titer were collected from several rootstocks trials to assess rootstock effect on tree growth under HLB disease pressure. Data were collected from a trial planted on trellis to examine the effect of tree manipulations on the length of time for transition from juvenility to maturity. This information will be valuable to accelerate the pace of development for new rootstocks and scions. Studies continue to assess citrus germplasm tolerance to Huanglongbing (HLB) and Phytophthora/Diaprepes in the greenhouse and under field conditions. In a new greenhouse study, Poncirus trifoliata, Cleopatra mandarin, and several hybrid selections were inoculated with HLB to further evaluate the apparent HLB tolerance in some trifoliata-type selections revealed in a previously completed greenhouse study. Greenhouse trees inoculated with Citrus tristeza virus (CTV) were tested for virus titer in preparation for CTV-induced decline evaluation of supersour rootstocks. More than fifty citrus genotypes and citrus relatives, as well as thousands of progeny from crosses, have been challenged by natural inoculation with Liberibacter in the field, and data are being collected on HLB symptoms and Liberibacter titer by PCR. Detailed information is being collected on HLB tolerance and tree performance in four rootstock field trials. All citrus germplasm and cultivars become infected with Liberibacter when inoculated, but different germplasm responds to HLB infection at different rates and with different symptom severity. Greenhouse and field studies are continuing to determine the most efficient methods to evaluate new citrus germplasm from crosses and transformation for resistance or tolerance to HLB. Preliminary evaluations were completed on gene expression in HLB-susceptible and HLB-tolerant selections to identify differences that can help guide selection from conventional breeding and transgenic efforts. In coordinated research between this grant and the FCATP transgenic citrus grant to USDA, selected anti-microbial, insect resistance, and other genes were inserted into outstanding rootstock and scion cultivars to develop new cultivars with resistance to HLB and Citrus Bacterial Canker. Efforts continue to transform trees with seven different promoters and three new anti-bacterial genes targeted at producing HLB-resistant cultivars. Testing of transgenic plants for HLB resistance continues under the resources provided by this grant. Genetic transformation was used to introduce the citrus FT gene for induction of early flowering into citrus scion and rootstock germplasm. Commercial field plantings of the new seedless mandarin cultivar ‘Early Pride’ were planned with cooperators. The final revision of the release notice for US-942 rootstock was prepared and submitted for official approval.