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Title: Apparent tolerance to huanglongbing in citrus and citrus-related germplasm

Author
item Miles, Godfrey
item Stover, Eddie
item Keremane, Manjunath
item RAMADUGU, CHANDRIKA - University Of California
item Lee, Richard

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2016
Publication Date: 2/3/2017
Citation: Miles, G., Stover, E., Keremane, M., Ramadugu, C., Lee, R.F. 2017. Apparent tolerance to huanglongbing in citrus and citrus-related germplasm. HortScience. 52:31-39.

Interpretive Summary: The disease huanglongbing (HLB) is devastating Florida citrus. In a Florida field planting, growth and huanglongbing (HLB) severity were assessed as indicators of HLB-tolerance on trees grown from seed of 83 diverse seed-source trees of citrus and citrus-relatives from the Riverside, California genebank. The HLB-pathogen and vector were abundant and trees were challenged for six years before data were collected in October and November of 2015. The healthiest trees with low or absent huanglongbing(HLB) symptoms were distant citrus-relatives. Within citrus most of the healthiest trees with densest canopies, little leaf loss, and greater growth, were those with pedigrees that included citron, the fruit used for the brightly colored bits in fruit cake. Percentage of citron in the pedigree significantly correlated with measures of tolerance. Although no commercial citrus genotypes yielded progenies with strong HLB resistance, in this field experiment several progenies maintained dense canopies and good growth, and may be useful in breeding HLB tolerant cultivars.

Technical Abstract: In a Ft. Pierce, Florida field planting, growth and huanglongbing (HLB) severity were assessed as indicators of HLB-tolerance on progenies of 83 seed-source accessions of citrus and citrus-relatives from the Riverside, California genebank. The HLB-pathogen (Candidatus Liberibacter asiaticus) and vector (Asian citrus psyllid, Diaphorina citri) were abundant and trees were challenged for six years before metrics (leaf mottle, percent canopy mottle, overall health, canopy density, canopy width, canopy height, and trunk diameter) were collected in October and November of 2015. The healthiest trees with low or absent HLB symptoms were distant citrus-relatives: Balsamocitrus daweii, Bergera koenigii, Casimiroa edulis, Clausena excavata, Murraya paniculata and one accession of Severinia buxifolia. Within citrus most of the healthiest trees with densest canopies, little leaf loss, and greater growth, were those with pedigrees that included C. medica. These included progenies of C. hybrid (‘Limon Real’), C. limetta, C. limettioides, C. limonia, C. medica, C. volkameriana, and some C. limon accessions. Trees in this category exhibited distinct mottle characteristic of HLB but maintained dense canopies and exhibited good growth. Trees from seed-source accessions without citron in their background were generally the least healthy overall with less dense canopies. The exception were progenies of two citrus aurantium accession which were markedly healthier than progenies of other non-citron-derived citrus seed-source accessions. Linear regression analysis, between metrics collected and pedigree of seed parent, indicates that percentage of citron in the pedigree significantly correlated with measures of tolerance. Although no commercial citrus genotypes yielded progenies with strong HLB resistance, in this field experiment several progenies maintained dense canopies and good growth, and may be useful in breeding HLB tolerant cultivars.