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In a Fort Pierce, FL, field planting, plant growth, and Huanglongbing (HLB) severity were assessed as indicators of HLB tolerance on progenies of 83 seed-source accessions of Citrus and Citrus relatives mainly from the Riverside, CA, genebank. The HLB-associated pathogen [Candidatus Liberibacter asiaticus (CLas)] and vector [asian citrus psyllid (ACP), Diaphorina citri] were abundant, and trees were naturally challenged for 6 years before metrics (leaf mottle, percent canopy mottle, overall health, canopy density, canopy width, canopy height, and trunk diameter) were collected in Oct. and Nov. 2015. The healthiest trees with low or no HLB symptoms were distant citrus relatives: Balsamocitrus dawei, 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 Citrus medica (citron). These included progenies of Citrus hybrid ('Limon Real'), Citrus limetta, Citrus limettioides, Citrus limonia, C. medica, Citrus volkameriana, and some Citrus limon accessions. Trees in this category exhibited distinct leaf-mottle characteristic of HLB and substantial pathogen titers, but maintained dense canopies and exhibited good growth. Trees from seed-source accessions in the genus Citrus without citron in their background were generally among the least healthy overall with less dense canopies. The exceptions were progenies of two Citrus aurantium accessions, which were markedly healthier than progenies of other Citrus seed-source accessions not derived from citron. Linear regression analysis, between metrics collected and pedigree of seed parent, indicated 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 for breeding HLB tolerant cultivars. [ABSTRACT FROM AUTHOR]

The Asian citrus psyllid (Hemiptera: Liviidae) transmits a bacterium responsible for huanglongbing, a serious citrus disease. Insecticidal control of the psyllid is a key tactic used to manage the disease, but host plant resistance may hold some promise and clues in the search for alternative tactics. Results of a field survey revealed that relatively large infestation densities of the psyllid developed on conventional Citrus (Rutaceae) and citrange (Rutaceae) cultivars but not on any of 6 Poncirus trifoliata (L.) Raf. (Rutaceae) cultivars. Poncirus trifoliata is a species closely related to Citrus, and citranges are hybrids of sweet orange and P. trifoliata. Reduced colonization by the psyllid on P. trifoliata was largely a result of reduced rates of oviposition. Poncirus trifoliata resistance to oviposition was not observed in 4 citrange cultivars. [ABSTRACT FROM AUTHOR]

Genetic traits in Poncirus trifoliata (Rutaceae) are known to confer resistance to colonization by the Asian citrus psyllid, but field surveys indicated these traits were not expressed in any of 24 simple hybrids between P. trifoliata and sweet orange. No resistance to colonization by the psyllid was observed in 14 other types of P. trifoliata hybrids. Three citrumelo hybrids appeared to be resistant in 1 survey, but in another survey, none of 6 citrumelos exhibited resistance. Interestingly, colonization was somewhat reduced on a hybrid with P. trifoliata in the pedigree of both parents, suggesting the possibility that traits suppressing oviposition may be recovered through similar crosses. [ABSTRACT FROM AUTHOR]