PLANT SCIENCES

An Inside View of Infection

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Science  03 Aug 2012:
Vol. 337, Issue 6094, pp. 504
DOI: 10.1126/science.337.6094.504-a
CREDIT: NIGEL CATTLIN/ALAMY

Huanglongbing, or citrus greening, which is caused by bacteria transmitted by psyllid insects, has devastated citrus trees in Asia and Africa and is becoming a considerable threat in North America. Affected trees produce damaged fruit and typically will die within a few years. Several control measures have been brought into play but with little effect. Chiyaka et al. have now developed a mathematical model of citrus greening that may lead to more effective control strategies. Key to the model is considering the diseased entity to be not the whole tree, but rather the flush, a new growth of young leaves that the psyllid insects find particularly attractive. The model generated several outcomes that match observed disease characteristics: that rapid movement of the bacteria within the tree results in death in about 5 years, and that the numbers of psyllid insects decline after the infection is well established. Some indications from the model suggested that nutritional support to the tree can help the tree sustain some healthy flush. Other indications suggest that insecticidal spraying is most effective when applied frequently and early in an infection. By designating the flush as the diseased entity, the authors leave room to consider infection spread within a tree, which can occur without the psyllid vector.

Proc. Natl. Acad. Sci. U.S.A. 109, 12213 (2012).

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