Title: HLB resistance and tolerance in citrus scion development at the US Horticultural Research Laboratory Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 5, 2012
Publication Date: January 23, 2013
Citation: Stover, E.W., Mccollum, T.G. 2013. HLB resistance and tolerance in citrus scion development at the US Horticultural Research Laboratory [abstract]. Florida Citrus Show, January 23-24, 2013, Ft. Pierce, FL. Technical Abstract: Huanglongbing (HLB) is severely impacting Florida citrus and threatening industries in the rest of the US. Productivity declines in many HLB-affected trees. Fruit size and quality often diminish as the disease advances. The USDA citrus scion breeding program is charged with producing improved citrus varieties for the US and resisitance/tolerance to HLB is now a major focus. 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. Many other hybrids appear to have substantial tolerance or resistance to HLB and experiments are underway to assess these traits. Evidence mounts that useful resistance/tolerance to HLB is present in cultivated citrus and this is a focus of the USDA citrus breeding program.