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Title: Evaluation of Liberibacter titer in field-infected trifoliate cultivars: Preliminary evidence for HLB (huanglongbing) resistance

Author
item Stover, Eddie
item Shatters, Robert - Bob
item McCollum, Thomas
item Hall, David
item Duan, Ping

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings
Publication Acceptance Date: 1/7/2011
Publication Date: 1/7/2011
Citation: Stover, E., Shatters, R., McCollum, G., Hall, D., and Duan, Y-P. 2011. Evaluation of Liberibacter titer in field-infected trifoliate cultivars: Preliminary evidence for HLB (hunglongbing)resistance. Proceedings of Florida State Horticultural Society. 123:115-117.

Interpretive Summary: Huanglongbing (HLB) and Asian citrus psyllid (ACP) are widespread at the Ft. Pierce USDA citrus grove, which is managed primarily as a site for research on HLB control and resistance. The variety collection at this grove includes rootstock cultivars on a mandarin rootstock and it has become apparent that many trifoliate hybrids show weaker symptoms of HLB than the rootstock shoots growing from the trees' bases. Therefore tests were run to compare levels of the HLB bacterium in trifoliate types and their rootstocks. In November 2009 random quadrant leaf-samples and a diagnostic “most symptomatic leaf” sample were collected from the test tree canopies, along with a random sample and diagnostic sample from the rootstocks. The two pure Poncirus trifoliata (trifoliate orange) had no or low-abundance of the HLB bacterium, as did two citranges (sweet orange x P. trifoliata hybrids), except that diagnostic samples and rootstock samples from the same citranges had a very high CLas titer. Variability was observed in rHLB bacterium among the ten citranges tested and all showed high bacterium levels in rootstock suckers. The data suggest that Poncirus and some Poncirus hybrids tolerate and/or suppress ther HLB bacterium even when grafted onto a high-titer source, and encourage further work on identifying and characterizing HLB resistance in Poncirus and its hybrids.

Technical Abstract: Huanglongbing (HLB) and Asian citrus psyllid (ACP) are widespread at the Ft. Pierce USDA citrus grove, which is managed primarily as a site for research on HLB control and resistance. The variety collection at this grove includes rootstock cultivars on a mandarin rootstock and it has become apparent that many trifoliate hybrids show weaker symptoms of HLB than the rootstock shoots growing from the trees' bases. Therefore tests were run to compare levels of the HLB bacterium in trifoliate types and their rootstocks. In November 2009 random quadrant leaf-samples and a diagnostic “most symptomatic leaf” sample were collected from the test tree canopies, along with a random sample and diagnostic sample from the rootstocks. The two pure Poncirus trifoliata (trifoliate orange) had no or low-abundance of the HLB bacterium, as did two citranges (sweet orange x P. trifoliata hybrids), except that diagnostic samples and rootstock samples from the same citranges had a very high CLas titer. Variability was observed in rHLB bacterium among the ten citranges tested and all showed high bacterium levels in rootstock suckers. The data suggest that Poncirus and some Poncirus hybrids tolerate and/or suppress ther HLB bacterium even when grafted onto a high-titer source, and encourage further work on identifying and characterizing HLB resistance in Poncirus and its hybrids.