Intra-population diversity between citrus viroid II variants described as agents of cachexia disease

The citrus viroid II (CVd‐II, Hop stunt viroid) variant, cachexia 909 (Ca‐909) has been designated as a “cachexia” disease isolate on the basis of inducing extremely mild symptoms on the cachexia indexing host Parson's Special mandarin (PSM). However, Ca‐909 lacks the six‐nucleotide cluster demonstrated to control the pathogenicity of cachexia inducing agents such as CVd‐IIc. Progeny populations of CVd‐IIc and Ca‐909 from the bioamplification host, Etrog citron, and the indexing host PSM were surveyed for clones with possible mutations in the locus of the “cachexia cluster”. The intra‐population diversity and the genealogical relationships among clones of CVd‐IIc and Ca‐909 populations were also analysed using principles of the coalescent theory. CVd‐IIc progeny was found not to mutate in the “cachexia cluster” and Ca‐909 did not acquire any mutations related to the nucleotide sites of the “cachexia cluster”. Specific mutations of the Ca‐909 progeny were found to be similar to the non‐cachexia variant, CVd‐IIa. Population profiles and genealogical patterns of CVd‐IIc and Ca‐909 in Etrog citron were not significantly different. However, although CVd‐IIc progeny were more conserved in PSM, Ca‐909 progeny displayed titre, population profiles, and genealogical patterns more uniform in selected tissues of Parson's Special mandarin than CVd‐IIc. These experimental approaches demonstrate the genetic stability of the cachexia‐agent CVd‐IIc and question the inclusion of Ca‐909 as a cachexia disease agent.