Cowpea mild mottle virus, a sometimes problem for French bean crops

Abstract

A carlavirus, closely related to cowpea mild mottle virus (CPMMV) and spread by silverleaf whitefly (SLW) was reported affecting fresh market beans in a major Australian growing district in 2016. Further investigations of this virus were completed through regular surveys of crops, weeds and SLW in this district from 2016–2019. Sequencing of the 3'end of the virus genome from a range of samples detected four variants, referred to as CPMMV:A:FB5288 and CPMMV:A:S1 to S3. The distribution of these four variants in survey samples showed the dominant variant in French bean crops as CPMMV:A:FB5288. The surveys also showed disease impacts were limited to autumn and varied over time. This variation is attributed to the influence of rainfall on adult insect vector levels. The experimental host range of CPMMV:A:FB5288 was shown to be limited to the Phaseoleae plant tribe and included the Australian native species, Glycine canescens. French bean varieties showed a range of susceptibilities to this dominant sequence variant from highly tolerant to very susceptible. The tolerant varieties provide the local industry with some options for disease management where previously there were none. Genetic diversity studies further highlight the need for taxonomic reform of the species referred to as CPMMV.