Our presentations at the Second International Research Conference on HLB in Orlando documented recent progress in characterizing HLB resistance/tolerance as found in Poncirus trifoliata and hybrids of that species with citrus. Some trifoliate hybrid citrus rootstocks, including US-802 and US-897, were demonstrated to become infected by HLB more slowly, to develop smaller amounts of bacterial even after infection, and to exhibit dramatically less symptoms in response to HLB infection than other citrus cultivars. A greenhouse experiment was initiated to compare the utility of the trifoliata-type resistance in the rootstock and scion position in grafted trees. Evidence was presented that documents significantly higher levels of some antimicrobial metabolites in the HLB-resistant trifoliate hybrid germplasm. Gene expression and metabolomic studies are underway to further characterize the genes and metabolites responsible for the resistance that can be used in creation and selection of conventional and transgenic varieties with improved tolerance or resistance to HLB. In this quarter, fruit quality, yield, and/or tree size data were collected from fourteen rootstock and scion field trials. Data was collected from one large cooperative rootstock trial with Ray Ruby grapefruit scion to evaluate rootstock effect on grapefruit quality and sheepnosing. Scion growth was measured on a greenhouse experiment to develop a more rapid way to evaluate CTV resistance and to evaluate supersour rootstocks for tolerance to four different decline strains of CTV. Rooted cuttings of supersour rootstock hybrids were budded with scions to propagate trees for field trials. One hundred supersour-type hybrids were selected from among new progeny for propagation and additional testing. A field trial was planted to compare HLB reaction of standard rootstock varieties to that of new transgenic rootstocks. Budded greenhouse trees for field trials were grown to planting size. Experiments continued to assess the utility of different methods for testing germplasm for resistance or tolerance to Asian Citrus Psyllid (ACP) and HLB disease. Data continued to be collected from four field experiments to assess the HLB tolerance of sweet orange trees on 15 different rootstocks. A field experiment continued to identify rootstocks with resistance to the Phytophthora-Diaprepes Complex. In coordinated research between this grant and the FCATP transgenic citrus grant to USDA, selected anti-microbial genes were inserted into outstanding rootstock and scion cultivars to develop new cultivars with resistance to HLB and Citrus Bacterial Canker (CBC). Rootstocks were transformed with an early flowering gene to produce selections that will allow more rapid advancement through generations and thus, more rapid genetic improvement. Selected transgenic rootstocks were challenged with HLB to assess potential resistance, including constructs with two new bacterial resistance genes. Research is continuing to use HLB responsive genes and promoters identified in a previously published gene expression study for engineering resistance in citrus. A microarray analysis was 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. This data is being analyzed now for publication and to guide future breeding and transformation research. The new hybrid rootstock US-942 was officially released for commercial use, based on outstanding performance in several different field trials. Seed of US-942 was provided for distribution to Florida citrus nurseries.