The so-called “leaf fleck” virus diseases of citrus

Authors: Krueger, Robert

Submitted to: Subtropics newsletter
Publication Type: Trade Journal
Publication Acceptance Date: 5/2/2019
Publication Date: 5/16/2019
Citation: Krueger, R. 2019. The so-called “leaf fleck” virus diseases of citrus. Subtropics newsletter. 19 Spring pages 5-11.

Interpretive Summary:

Technical Abstract: Although most current attention and research in citrus diseases is directed towards Huanglongbing, other citrus diseases are also relevant. One group of virus-associated diseases is the so-called “leaf fleck” diseases: concave gum (CG), cristacortis, and impietratura. This name is due to the symptoms produced in indicator plants. Although these symptoms are similar, the effect of these viruses on commercial or field-grown trees are quite different. Concave gum and cristacortis produce, pits of different morphology on the trunk and branches, whereas impietratura produces gumming in the fruit. All three can debilitate a tree and cause economic losses. Until recently, these diseases were assumed to be caused by viruses but the identity of these viruses had not been demonstrated. Recently, a new virus associated with concave gum was identified using next generation sequencing. This virus was appropriately named “Citrus concave gum associated virus” (CCGaV). Another closely related virus, “Citrus virus A” (CiVA) was identified by the same team and found to occur separately and in conjunction with CCGaV in trees with and without CG symptoms. Other groups identified a concave gum isolate from California and an impietratura isolate from Spain with CiVA, whereas a cristacortis isolate from Corsica appeared more closely related to CCGaV. Several other groups have recently reported other leaf flecking diseases associated with viruses closely related to CCGaV and CiVA. Now that actual viruses have been identified, a broader range of isolates needs to be evaluated to further clarify the relationships between viruses and symptoms expression.