Pathogenicity of a Natural Recombinant Associated with Ageratum Yellow Vein Disease: Implications for Geminivirus Evolution and Disease Aetiology

Abstract

Yellow vein disease of Ageratum conyzoides is caused by a viral DNA complex consisting of the genomic component (DNA A) of the monopartite begomovirus Ageratum yellow vein virus (AYVV, family: Geminiviridae) and a small satellite-like DNA β component. AYVV DNA A is unable to induce symptoms in this host alone but can systemically infect A. conyzoides in which it accumulates to low levels. Here, we demonstrate that the yellow vein phenotype can also be produced by co-inoculating A. conyzoides with AYVV DNA A and recDNA-Aβ17, a naturally occurring recombinant of approximately the same size as DNA β that contains sequences from both DNA A and DNA β. Symptoms induced by DNA A and recDNA-Aβ17 in A. conyzoides and Nicotiana glutinosa are qualitatively similar to those associated with DNA A and DNA β although milder. Recombination between DNA A and DNA β to produce a chimera resembling recDNA-Aβ17 was observed after whitefly transmission of the disease in A. conyzoides. Hence, such recombination events are likely to occur frequently, implying that recombinants will normally be associated with this type of disease complex in the field. Possible implications of these findings for the evolution of begomoviruses and the aetiology of their diseases are discussed.