|Nguyen, M. C.|
|Le, Q. D.|
|Parker, P. E.|
Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 12/17/2008
Publication Date: 5/1/2010
Citation: Gottwald, T.R., Hall, D.G., Beattie, G., Bar-Joseph, M., Lapointe, S.L., Stover, E.W., Parker, P., Mccollum, T.G., Hilf, M.E. 2010. Investigations of the effect of guava as a possible tool in the control/management of Huanglongbing. International Organization of Citrus Virologists Proceedings. Interpretive Summary: Citrus huanglongbing (HLB) is a serious bacterial disease of citrus that first discovered in the Western Hemisphere in 2004. Since then it has been found in Florida, Brazil, throughout the Caribbean, and a few places in Central America including Mexico. In Florida as elsewhere in the world, this disease is not under adequate control. Therefore it is a great threat to the citrus industries of the United States. This article presents a very unique potential control methodology for HLB. The farmers of the Mekong Delta of Vietnam have discovered a unique interaction between citrus and guava, a tropical fruit tree, that extends the commercial life of citrus plantings plagued by HLB. Apparently the guava plants release volatile chemicals into the air that repel the insects that vector HLB. This is never been attempted in the Western Hemisphere. The article describes citrus and guava interplantings are established in the United States, specifically in Florida and Texas to test the protective effect of guava. The article also describes a series of experiments in the greenhouse in which citrus plants, with and without guava companion plants are exposed to insect vectors. In these experiments, the survival of the HLB vectors was much reduced when guava plants were present. The article also explains that there may be additional plants in the same plant family as guava, that might also be useful to repel harmful insects. If successful, the use of such interplantings could potentially be a valuable tool to help control HLB in the Western Hemisphere.
Technical Abstract: The farmers of the Mekong Delta of Vietnam have discovered a unique interaction between citrus and guava, Psidium guajava L., that extends the commercial life of citrus plantings plagued by huanglongbing (HLB). Due to HLB, the normal life of citrus plantings in the region is 2-4 years. However, when interplanted with white guava, plantings can survive for up to 15 yr. Vietnamese/Japanese/Australian collaborative research projects have demonstrated that psyllid vector populations are reduced to near non-detectable levels in interplantings compared to citrus monocultures. The Florida research project described here is an attempt to adapt and determine the feasibility of this discovery to Western citriculture conditions. White guava, determined to be genetically similar to that grown in Vietnam, and pink guava have since been tested in greenhouse studies in Florida. High adult mortality rates occurred when psyllids were confined to guava in no-choice situations, with 95% mortality occurring within 6-9 days. Mortality rates of adults confined to tomato or cotton were similar while near 100% survival was observed on citrus. Adults generally found citrus faster when citrus was caged alone than when it was caged with guava, and lower numbers of adults were consistently observed on citrus over time in cages with both citrus and guava. The effect may be due to volatile compounds produced by guava that are deleterious to psyllids. Mortality rates of adult psyllids in cages with citrus and guava were significantly greater than in cages with citrus alone in one experiment but not another. The results of the two experiments were similar with respect to mortality rates of adults in cages with just citrus. The effect of various volatile extracts on psyllid behavior and survival are under investigation. In addition, large-scale replicated field plots have been established in multiple locations in Florida to examine the dynamics of HLB epidemics in citrus/guava interplantings versus citrus monocultures. Mekong farmers often use spray oils (agricultural and horticultural mineral oils) in lieu of insecticides in addition to guava to inhibit psyllid populations. This same strategy is presently under investigation in Florida.