Phytoplasma recovery phenotype-a case study for aster yellows in South Africa

Aster yellows phytoplasma (AY) is associated with grapevine yellows disease in South Africa that has been observed in local vineyards since 2006. The disease rapidly spread through its natural insect vector and is responsible for significant yield losses in affected production areas. The lack of effective control measures prompted producers to adopt alternative measures, such as inducing the so-called recovery phenotype in infected grapevines. In South African vineyards, this is done by coppicing, i.e. cutting symptomatic plants just above the graft union, and allowing regrowth of a single shoot. These shoots typically display the recovery phenotype-a complete remission in symptom expression, as well as testing negative in nested-PCR assays. In this study, the recovery phenotype was monitored in a production vineyard over three growing seasons, by PCR-screening of individual infected and uninfected, coppiced and non-coppiced plants for the presence of AY. A severe drought that occurred during the latter part of 2016 until 2018 influenced the results dramatically.