|GUPTA, GOUTAM - New Mexico Consortium|
|Baldwin, Elizabeth - Liz|
Submitted to: International Research Conference on Huanglongbing
Publication Type: Abstract Only
Publication Acceptance Date: 2/7/2019
Publication Date: 3/1/2019
Citation: Stover, E.W., Driggers, R.E., Krystel, J.A., Hao, G., Hall, D.G., Gupta, G., Hartung, J.S., Baldwin, E.A., Bai, J., Plotto, A., Manthey, J.A. 2019. USDA efforts to develop resistance and tolerance to huanglongbing in citrus scions[abstract]. International Research Conference on Huanglongbing, March 12-15, 2019, Riverside, California.
Interpretive Summary: Tolerance to huanglongbing (HLB) is present in some cultivated citrus and greater resistance may be drawn from more distant members of the gene pool. Strong resistance and even immunity should be possible using genetic engineering. Efforts are underway to produce HLB-resistant or tolerant scions in the United States Department of Agriculture (USDA) citrus breeding program.
Technical Abstract: HLB (huanglongbing)-resistant or -tolerant cultivars will be essential to sustain the Florida citrus industry, with solutions needed in the short and long term. Potentially useful tolerance to HLB is present in cultivated citrus and greater resistance is apparent in more distant members of the gene pool. Several mandarin hybrids, including some released cultivars, display sustained growth and canopy health despite prolonged HLB infection. In a replicated trial of 50 selections and cultivars, decline in canopy growth appears to be a marked indicator of HLB-susceptibility even while trees are superficially healthy. This was not evident until after four years of field growth, even though trees were infected pre-planting. Several genotypes with Poncirus in the pedigree continue to show strong HLB-tolerance but not resistance. A Poncirus-derived scion cultivar, US SunDragon was released with this attribute, is being used in breeding, and some progeny are now fruiting. Hybridization is ongoing to combine HLB-tolerance from Poncirus and mandarin sources. Juice quality assessments are underway to explore juice blends from HLB-tolerant material. Several transgenics are showing reductions of Candidatus Liberibacter asiaticus (CLas) titer by 100-800 X and are now in field trials with the promise of greater HLB control than is seen in conventional material. The most successful transgenics to date are expressers of: a modified plant thionin; chimeras derived from the citrus proteome with membrane binding and lytic peptides connected by a linker; and ScFv directed at a CLas membrane protein or a protein secreted by CLas. It must be noted that pre-HLB Florida citrus plantings typically did not provide a return on investment until 7-8 years after planting. Validation of economic tolerance to HLB will likely require ten or more years of replicated field trials in multiple locations. Our best conventional and transgenic material has or is undergoing cleanup at FDACS DPI to facilitate such trials.