|RAMADUGU, CHANDRIKA - University Of California Agriculture And Natural Resources (UCANR)|
|HALBERT, SUSAN - Florida Department Of Agriculture|
|ROOSE, MIKEAL - University Of California Agriculture And Natural Resources (UCANR)|
|LEE, RICHARD - Retired ARS Employee|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2016
Publication Date: 4/22/2016
Citation: Keremane, M.L., Ramadugu, C., Halbert, S., Duan, Y., Roose, M., Stover, E.W., Lee, R. 2016. Long term field evaluation reveals HLB resistance in Citrus relatives. Plant Disease. http://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-03-16-0271-RE.
Interpretive Summary: Citrus huanglongbing, also known as greening is a devastating disease of citrus which has destroyed more than 50% of the multibillion dollar citrus industry within ten years of introduction. Most citrus cultivars are highly susceptible to this disease. In order to find sources of resistance, we took germplasm resources available in Riverside, CA and planted over 800 plants belonging to 100 accessions including many citrus relatives and conducted extensive observations and analysis. Excellent sources of resistance was found in two citrus relatives, dessert lime and finger lime. Both belong to non-citrus genera, but are sexually compatible with citrus. Screening of some available natural hybrids showed that the resistance can be transferred to citrus by breeding
Technical Abstract: Citrus huanglongbing (HLB) is a destructive disease with no known cure. To identify sources of HLB resistance in the subfamily Aurantioideae to which citrus belongs, we conducted a six-year field trial under natural disease challenge conditions in an HLB endemic region. The study included 65 Citrus accessions and 33 accessions belonging to 20 other closely related genera. For each accession, eight seedling trees were evaluated. Based on qPCR analysis of the pathogen titers and disease symptoms, eight disease response categories were identified. We report two immune, six resistant and 14 tolerant accessions. Resistance/tolerance observed in different accessions may be attributed to a multitude of factors including psyllid colonization ability, absence of pathogen multiplication, transient replication of the bacterium, delayed infection, or lack of pathogen establishment in the plant. Of the 38 accessions that were highly susceptible but retained their leaves, 13 were citrons, lemons and limes. Resistance and high level of field tolerance were observed in many non-citrus genera. Disease resistance/tolerance was observed in Australian citrus relatives, Eremocitrus and Microcitrus, which are sexually compatible with citrus and may be useful in future breeding trials to impart HLB resistance to cultivated citrus.