Developing resistance to citrus huanglongbing.
C. RAMADUGU (1), M. Keremane (2), T. McCollum (3), D. Hall (3), M. Roose (1) (1) University of California Riverside, U.S.A.; (2) USDA ARS National Clonal Germplasm Repository for Citrus and Dates, U.S.A.; (3) US Horticultural Research Laboratory, U.S.A.
Citrus huanglongbing (HLB) has caused significant damage to citrus industries in Florida and Brazil. The disease is associated with a fastidious bacterium, Candidatus Liberibacter asiaticus (Las) and transmitted by psyllids. Development of HLB resistant rootstock and scion cultivars will be beneficial to the industry. Sources of HLB resistance are not known in the genus Citrus. We have demonstrated HLB resistance in Eremocitrus and Microcitrus which are closely related genera sexually compatible with Citrus. Naturally occurring hybrids of Citrus with Eremocitrus and Microcitrus parentage were exposed to the HLB pathogen under greenhouse conditions and determined to be HLB resistant in controlled experiments. Since the resistance from these non-Citrus genera appears to be heritable, we have generated about 800 mandarin and trifoliate hybrids using Eremocitrus and Microcitrus as pollen parents. The hybrid seeds were raised in greenhouses in Florida and challenged by feeding with LAS-positive psyllids for four weeks. Preliminary results indicate the absence of Las in many hybrids. We are monitoring the putative resistant hybrid plants continuously by assaying for the presence of Las by qPCR and digital PCR, and also by observing the hybrids for expression of disease symptoms. We will confirm resistance after conducting no-choice psyllid feeding experiments.