In-grove spatio-temporal spread of citrus huanglongbing and its psyllid vector in relation to rain

Authors: SHIMWELA, MPOKI - University Of Florida; HALBERT, SUSAN - Florida Department Of Agriculture; Keremane, Manjunath; MEARS, PAUL - Florida Department Of Agriculture; SINGER, BURTON - University Of Florida; LEE, WON - University Of Florida; JONES, JEFF - University Of Florida; PLOETZ, RANDY - University Of Florida; VAN BRUGGEN, ARIENA - University Of Florida

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2018
Publication Date: 12/7/2019
Citation: Shimwela, M.M., Halbert, S.E., Keremane, M.L., Mears, P., Singer, B.H., Lee, W.S., Jones, J.B., Ploetz, R.C., Van Bruggen, A.H. 2019. In-grove spatio-temporal spread of citrus huanglongbing and its psyllid vector in relation to rain. Journal of Phytopathology. 109(3):418-427. https://doi.org/10.1094/PHYTO-03-18-0089-R.
DOI: https://doi.org/10.1094/PHYTO-03-18-0089-R

Interpretive Summary: Citrus greening, huanglongbing (HLB) disease, is a significant threat to the U.S. citrus industry, and is caused by pathogenic bacteria carried by vectors, such as the Asian-Citrus-Psyllid (ACP). To understand the spread of the disease, more information is required correlating the spatial distribution of infected trees, with the presence of the causative bacteria, Candidatus Liberibacter asiaticus (Las), and the movement of psyllids. In this report, movement of Asian citrus psyllids with and without bacteria, and movement of citrus HLB were monitored in two neighboring commercial groves in Central Florida and a small third grove in Northern Florida. In addition to production of young flush by plants, various environmental factors like maximum and minimum temperature, rainfall and humidity were taken into consideration in building a model for understanding the disease spread and incubation period in the plant. The study showed that the epidemic front was linear and a gap of about six months existed between the first detection of Las in trees and appearance of disease symptoms. However, it was not possible to determine when the plants actually became infected in this field study. An important finding of the study was the positive relationship between Las-positive ACP and HLB and rainfall, as opposed to relative humidity or temperature. A positive correlation between flush abundance and Las-positive ACP was found in spring, fall and winter, but not in summer, probably because of inhibiting high temperatures.

Technical Abstract: Spatial distributions of citrus trees with huanglongbing (HLB), by Candidatus Liberibacter asiaticus (Las), and Asian-Citrus-Psyllid (ACP) have been described previously but reports on distributions of Las-infected (a)symptomatic trees and Las-positive ACP are rare, as are relationships between weather and ACP and HLB. Hypotheses: (i) incubation period can be estimated from spread of Las-positive asymptomatic and symptomatic trees, (ii) symptomatic tree distributions reflect those of Las-positive ACP, (iii) Las-positive ACP and citrus trees are related to rainfall. Surveys were done on Las-presence in (a)symptomatic trees in a small grove and on HLBincidence and (Las-positive) ACP in two commercial groves. Spread of symptomatic trees closely followed that of asymptomatic Laspositive trees with <6 months delay (incubation period). Las-positive (a)symptomatic fronts moved at 2.5-3.6 m month-1. No spatial relationship was detected between ACP and HLB. Rainfall correlated with HLB and Las-positive ACP.