Author
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McCollum, Thomas |
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Submitted to: International Research Conference on Huanglongbing
Publication Type: Proceedings Publication Acceptance Date: 2/7/2019 Publication Date: N/A Citation: N/A Interpretive Summary: “Early detection” of candidatus liberibacter asiaticus (CLas) infections in citrus trees followed by removal of infected trees is one of the three tenets of Huanglongbing (HLB) management. Although early detection actually refers to detection prior to visible HLB symptoms, the window of time between infection and symptom expression is a rather nebulous concept. This research was conducted to determine the efficacy of PCR for pre-symptomatic detection of CLas infections and to quantify the time between infection and appearance of HLB symptoms. Technical Abstract: To be considered “early detection” Candidatus Liberibacter asiaticus (CLas) infections must be identified prior to the appearance of Huanglongbing (HLB) symptoms. HLB symptoms can be ambiguous, however, the greatest number of confirmed infections from field surveys are from symptomatic leaves. Experiments described herein were conducted to determine the effectiveness of qPCR to predict HLB development in eleven commercial citrus scion types. CLas inoculations were conducted by confining populations of experimental trees with CLas-infected asian citrus psyllid (ACP) (ca. 3 wk exposure). Following ACP exposure the trees were disinfested of ACP and then held free of ACP during subsequent HLB symptom evaluations. Petiole samples were collected from young leaves that had been fed on by the inoculative ACP, and assayed for CLas infection by quantitative polymerase chain reaction (qPCR), typically one month following ACP exposure, but in some experiments subsequent assays were conducted multiple times post exposure. In addition to testing for CLas, trees were evaluated for the development of HLB symptoms. Based on results of the first CLas assay conducted following ACP exposure, 79% of trees that tested CLas negative at the first time following ACP exposure were never rated HLB symptomatic, and 75% of the trees that tested CLas positive were subsequently rated HLB symptomatic. In trees that were rated HLB symptomatic, the time of symptom appearance was typically within four to six months following ACP exposure, at which time CLas titers were greater than 103 copies per mg fresh wt of petiole. These results demonstrate that PCR can predict the development of HLB with 79% accuracy at one month following exposure to CLas infected ACP and that HLB symptoms become apparent within six months following ACP exposure. Although these experiments were conducted with small trees in the greenhouse, it is not unlikely that the results will be consistent for citrus in the field. |
