Incidence of RNA viruses infecting taro and tannia in East Africa and molecular characterisation of dasheen mosaic virus isolates

Abstract

Taro (Colocasia esculenta) and tannia (Xanthosoma sp.) plants growing in 25 districts across Ethiopia, Kenya, Tanzania and Uganda were surveyed for four RNA viruses.Leaf samples from 392 plants were tested for cucumber mosaic virus (CMV), dasheen mosaic virus (DsMV), taro vein chlorosis virus (TaVCV) and Colocasia bobone disease-associated virus (CBDaV) by RT-PCR. No samples tested positive for TaVCV or CBDaV, while CMV was only detected in three tannia samples with mosaic symptoms from Uganda. DsMV was detected in 40 samples, including 36 out of 171 from Ethiopia, one out of 94 from Uganda and three out of 41 from Tanzania, while none of the 86 samples from Kenya tested positive for any of the four viruses. The complete genomes of nine DsMV isolates from East Africa were cloned and sequenced.Phylogenetic analyses based on the amino acid sequence of the DsMV CP-coding region revealed two distinct clades. Isolates from Ethiopia were distributed in both clades, while samples from Uganda and Tanzania belong to different clades. Seven possible recombination events were identified from the analysis carried out on the available 15 full-length DsMV isolates. Nucleotide substitution ratio analysis revealed that all the DsMV genes are under strong negative selection pressure.

Journal of Plant Protection Research

“…Many codons in the CP sequence are under negative selection also those localized in the beginning of the N-domain containing DAG motif region, which is responsible for aphids transmission. These results are consistent with those obtained by Kidanemariam et al (2021). Strong purifying selection is often observed for functional proteins where the majority of amino acids are largely invariable due to strong structural and functional constraints.…”

“…Our results confirmed that DsMV population is being shaped by recombination (Wang et al 2017;Kidanemariam et al 2021). Recombination is an important evolutionary factor involved in plant virus populations genetic variation and evolution.…”

“…al. (2017) and Kidanemariam et al (2021) indicated that DsMV isolates grouped into two clades and groupings were not correlated with the geographical origin however, there was some correlation with the host. Further studies using larger data sets are required to analyze the host-associate traits.…”

Taro in West Africa: Status, Challenges, and Opportunities

“…For example, the co-infection of taro with taro bacilliform virus (TaBV) and Colocasia bobone disease virus (CBDV) is thought to be lethal to the crop. TaBV, along with taro bacilliform CH virus (TaBCHV) diseases [59] and dasheen mosaic virus disease [10], has been reported in Africa. Several other taro viruses have also been found in the Pacific, which currently restricts international movement of germplasm; thus, many countries do not have access to agronomically elite genotypes and selected traditional cultivars.…”

“…Taro is an important food crop for millions of people in many parts of Africa, where it is widely grown as a backyard crop and an intercrop [6][7][8][9][10]. It is also used as an ornamental plant [11].…”