Next generation sequencing reveals past and current widespread occurrence of maize yellow mosaic virus in South Africa

Abstract

Maize yellow mosaic virus (MaYMV) is a single-stranded RNA polerovirus first identified in China. MaYMV was recently reported from West and East Africa, however it had not yet been reported from southern Africa. RNA-seq data from South African field-grown fungal-infected maize was mined for viral sequences by de novo assembly of reads that did not map to the maize or fungal genomes. Predicted proteins from the de novo-assembled unmapped reads matched MaYMV proteins with regions of 96–100% identity. MaYMV was detected in maize RNAseq data from 2009, 2012 and 2013. Complete South African MaYMV genome sequences (5642 nt) were determined by RT-PCR and Sanger sequencing of samples from two different maize genotypes, years, and sites. Phylogenetic analysis confirmed the species identity as MaYMV, and showed separate clustering of isolates between Africa, Asia and South America. Some MaYMV positive samples had reads matching Potyviridae (Johnson grass mosaic virus and Sugarcane mosaic virus), and mycoviruses (Setosphaeria turcica hypovirus 1, Bipolaris maydis partitivirus 1, and Pleospora typhicola fusarivirus 1). A 2016/2017 RT-PCR survey of maize plants exhibiting virus-like symptoms, such as yellowing and streaking patterns, revealed MaYMV in 39 samples from six provinces in South Africa. This report documents the earliest known MaYMV infection world-wide, and indicates that the virus is widespread throughout Africa.