Detection of Greening in Sprouts from Citrus Tree Stumps

ADDITIONAL INDEX WORDS. Candidatus Liberibacter asiaticus, Florida citrus, greening eradication A study was initiated to determine if stump sprouts from citrus trees that were removed because of visual citrus greening (huanglongbing, HLB) symptoms tested positive for Candidatus Liberibacter asiaticus (Ca. Las). The study was conducted in a commercial grove in DeSoto County, FL. All trees selected for the trial were visually determined to have HLB prior to removal. The 15 trees selected were removed using a standard tree shear mounted to a front-end loader. Remaining stumps were monitored on 30-day intervals to detect sprout formation from the stump or exposed lateral roots. Once sprouts appeared, the entire stump and exposed lateral roots were enclosed within a screen enclosure to exclude psyllids from feeding on new vegetative growth. At 160 days after clipping, leaf and stem tissues from sprouts were tested for Ca. Las by the DNA-based quantitative PCR (qPCR) method. During the study, 12 of the stumps spr outed and produced 2 to 26 sprouts per stump. Two of 12 stumps that sprouted had insuffi cient vegetative plant material to test. Eight of the 10 stumps (80%) had one or more sprouts that were greening positive. The percentage of greening positive sprouts recovered from a positive stump ranged from 33% to 100%. The broad range in percent greening positive sprouts from an individual stump refl ects the uneven distribution of Ca. Las in the roots and trunk of infected trees. Controlling root and stump sprouts after removal of greening infected trees is essential in its control and spread. Citrus greening (huanglongbing, HLB) is a very serious disease resulting in tree decline and subsequent death. The disease causes phloem necrosis and is associated with the bacterium Candidatus Liberibacter asiaticus (Ca. Las). HLB affects all citrus cultivars. Early symptoms of decline include reduced fruit size, quality, yield, and eventually tree death after a number of years. The pathogen, Ca. Las, and its vector the Asian citrus psyllid (Diaphorina citri Kuwayama) are currently found throughout Florida (Gottwald et al., 2007). Symptoms in the plant include an asymmetrical chlorosis or blotchy pattern in the leaves, yellow veins and/or lopsided fruit along with other symptoms. As the disease progresses, yellow shoots and defoliated twig dieback occurs. Visual diagnosis of the greening is often confi rmed by quantitative PCR (qPCR) testing of symptomatic tissue in the laboratory (Southern Gardens Diagnostic Laboratory, Clewiston, FL; ). The bacterium can be distributed throughout the tree in the phloem including the roots (Tatineni et al., 2008). In studies by Lopes et al. (2007), pruning to remove symptomatic branches or the entire tree was ineffective for eliminating infected tissue and saving the affected tree. Currently, a common practice is to treat the cut surface of the cut stump with an herbicide material to prevent sprouting from the stump or roots. Materials labeled for these treatments include various glyphosate formulations (Futch and Singh, 2009) and triclopyr (Remedy® Ultra, Dow AgroScience). The study reported here was conducted to determine if sprouts that grow from stumps or exposed roots of citrus trees that were visually diagnosed with greening symptoms are later positive for HLB.

Topic: Phytoplasmas and Hemiptera pathogens
Subfield: Plant Science
Field: Agricultural and Biological Sciences
Domain: Life Sciences