Project Number: 2036-21000-010-13-R
Project Type: Reimbursable
Start Date: Oct 1, 2013
End Date: Apr 30, 2015
We have conducted a 4-year field trial in Picos farm, USDA Fort Pierce (with a very high level of disease pressure) with about 850 trees representing over 100 accessions to study HLB resistance in citrus. Varying degrees of resistance/tolerance was observed in some accessions, which warrants further study. Six trees of C. latipes remained symptomless without detectable LAS while two others became severely symptomatic. Similar phenomenon was observed in citranges. SCFS citron was highly susceptible, but was able to grow well and retain dense foliage. Resistance to HLB in citrus is extremely valuable. We propose to investigate, if partial resistance found in some citrus and citrus hybrids is due to host genetic variability (due to open pollination), escape from psyllid infestation and, if the resistance occurs only at the insect transmission level or also at the pathogen level (graft transmission). We also propose to analyze LAS populations in various resistance/tolerance situations.
Mikeal Roose and Chandrika Ramadugu (UCR) have expertise in conducting genetic analysis of individual clones by various methods including SSR analysis and sequencing of selected nuclear genes to determine if the individual trees are nucellar trees or hybrids. Genetic analysis of LAS populations will be conducted at USDA ARS Riverside in cooperation with Yongping Duan. Lee's lab (USDA ARS, Ft. Pierce) has been conducting HLB research for several years. Clonal propagations of selected trees will be maintained in Ed Stover's greenhouse (USDA ARS, Ft. Pierce). Insect transmissions will be conducted in cooperation with David Hall (USDA ARS, Ft. Pierce). Year 1: Collection of samples from individual trees and tissues for genetic analysis; establishment of promising clonal populations in greenhouse; propagation of trees for insect and graft transmission; start genetic analysis of host and pathogen Year 2: Establish insect and graft transmission studies and analyze plants over a period of two years at 3-month intervals; complete genetic analysis of host and pathogen from various tissues; analyze results and publish.