Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: Genetic Improvement of Citrus for Enhanced Resistance to Biotic and Abiotic Stresses

Location: Subtropical Insects and Horticulture Research

Title: Resistance and tolerance to huanglongbing in citrus

Authors
item Stover, Ed
item McCollum, Thomas
item Driggers, Randall
item Lee, Richard
item Shatters, Robert
item Duan, Ping
item Ritenour, Mark -
item Chaparro, Jose -
item Hall, David

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 2014
Publication Date: N/A

Interpretive Summary: Huanglongbing (HLB) is severely impacting Florida citrus. Productivity declines in many HLB-affected trees. Fruit size and quality often diminish as the disease advances. HLB was assessed in various citrus varieties in commercial groves with high HLB-incidence. ‘Temple’ had the lowest HLB symptoms and levels of the causal bacterium, while ‘Murcott’ and ‘Minneola’ had the highest. The USDA Ft. Pierce, FL farm is managed to allow us to see differences in variety responses to HLB. Some current citrus varieties and new hybrid seedlings demonstrate resistance/tolerance, at least to strain(s) of the HLB causing bacterium present on this site. The inedible trifoliate orange appears to be the citrus source with strongest resistance to HLB. Some citrus varieties and hybrids being evaluated by the breeding program have strong HLB leaf symptoms, but leaves are retained on the trees and fruit set and fruit size appear normal. In 3-years of data from a replicated trial of ‘Triumph’(T), ‘Jackson’(J), ‘Flame’(F), and ‘Marsh’(M), HLB symptoms were severe in all trees. However, the true grapefruit types F&M were almost completely defoliated in some years while grapefruit-like varieties T&J had full canopies. Cumulative fruit/tree was greater for T&J (255&220) than for F&M (29&66). T&J fruit met commercial standards and had normal size but F&M fruit were unacceptable with many small and misshapen. Evidence mounts that useful resistance/tolerance to HLB is present in cultivated citrus and this is a focus of the USDA citrus breeding program.

Technical Abstract: Huanglongbing (HLB) is severely impacting Florida citrus. Productivity declines in many HLB-affected genotypes, often with greatly thinned canopies. Fruit size and quality are often adversely affected as the disease advances. HLB was assessed in diverse cultivars in commercial groves with high HLB-incidence. ‘Temple’ had the lowest HLB symptoms and Liberibacter (Las) titer, while ‘Murcott’ and ‘Minneola’ had the highest. The USDA Ft. Pierce, FL farm is managed to reveal genotype responses to HLB. Some current cultivars and hybrid seedlings demonstrate resistance/tolerance, at least to strain(s) of Las present. C. trifoliata is the best documented citrus resistance source with Las titers suppressed even when C. trifoliata is grafted onto severely-infected rootstocks. Some cultivars and hybrids have abundant foliage symptoms, but full canopies and seemingly normal fruit set and size. In 3-years of data from a replicated trial of ‘Triumph’(T), ‘Jackson’(J), ‘Flame’(F), and ‘Marsh’(M), HLB symptoms were severe in all trees and Liberibacter titers were similar. However, F&M were almost completely defoliated in some years while T&J had full canopies. Cumulative fruit/tree was greater for T&J (255&220) than for F&M (29&66). T&J fruit met commercial standards and had normal size but F&M fruit were unacceptable with many small and misshapen. Evidence mounts that useful resistance/tolerance to HLB is present in cultivated citrus and this is a focus of the USDA citrus breeding program.

Last Modified: 12/18/2014
Footer Content Back to Top of Page