Abstract
A systematic search for viral infection was performed in the isolated Kerguelen Islands, using a range of polyvalent genus-specific PCR assays. Barley yellow dwarf virus (BYDV) was detected in both introduced and native grasses such as Poa cookii. The geographical distribution of BYDV and its prevalence in P. cookii were analyzed using samples collected from various sites of the archipelago. We estimate the average prevalence of BYDV to be 24.9% in P. cookii, with significant variability between sites. BYDV genetic diversity was assessed using sequence information from two genomic regions: the P3 open reading frame (ORF) (encoding the coat protein) and the hypervariable P6 ORF region. The phylogenetic analysis in the P3 region showed that BYDV sequences segregate into three major lineages, the most frequent of which (Ker-I cluster) showed close homology with BYDV-PAV-I isolates and had very low intra-lineage diversity (0.6%). A similarly low diversity was also recorded in the hypervariable P6 region, suggesting that Ker-I isolates derive from the recent introduction of BYDV-PAV-I. Divergence time estimation suggests that BYDV-PAV-I was likely introduced in the Kerguelen environment at the same time frame as its aphid vector, Rhopalosiphum padi, whose distribution shows good overlap with that of BYDV-Ker-I. The two other lineages show more than 22% amino acid divergence in the P3 region with other known species in the BYDV species complex, indicating that they represent distinct BYDV species. Using species-specific amplification primers, the distribution of these novel species was analyzed. The high prevalence of BYDV on native Poaceae and the presence of the vector R. padi, raises the question of its impact on the vulnerable plant communities of this remote ecosystem.
Highlights
Because of their isolation, restricted biota and harsh environments, Antarctic and sub-Antarctic terrestrial ecosystems are relatively simple, but highly vulnerable to biotic and abiotic perturbations
The results show that Barley yellow dwarf virus (BYDV)-PAV-I is the most prevalent species and that it is much more prevalent in the native P. cookii, it has been detected in a few other native and introduced grasses, but at a much lower rate
Since BYDV is known to be able to infect many members of the Poaceae family [16], the virus was sought in various other grass species, with a higher sampling intensity in successive years in sites where high BYDV prevalence had been observed in P. cookii
Summary
Because of their isolation, restricted biota and harsh environments, Antarctic and sub-Antarctic terrestrial ecosystems are relatively simple, but highly vulnerable to biotic and abiotic perturbations. The Kerguelen Islands (7215 km2), which comprise the second most isolated archipelago on earth, are located close to the Antarctic Polar Frontal Zone (APFZ), a major oceanic and climatic boundary They constitute an exceptional site as biological monitoring has been performed there for more than 35 years, providing an excellent knowledge of their paucispecific fauna and flora which are mostly distributed in a limited altitudinal range along the coasts [1]. These studies concerned the abundance, phenology, and distribution of native and introduced species [2] as well as community dynamics in a changing environment [3,4]. Relevant for plant viruses is the fact that only five aphid species are known to be present in the Kerguelen archipelago (only three species in the wild, outside of glasshouses) [6] and that all of them appear to be relatively recent introductions during the second half of the 20th century (Voisin, personal communication, and [7])
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