Perofascia is not monotypic: the description of the second taxon affecting the South American crop maca (Lepidium meyenii)

Maca (Lepidium meyenii) is an Andean crop of narrow distribution, but because of the nutritional and health value, its cultivation area is rapidly expanding. By a broad-spectrum resistance mechanism against various pathogens, just a few diseases have been reported on maca, among which downy mildew is a potential threat to its cultivation. The occurrence of this disease was, so far, restricted to the native area of maca. However, here we report that it was recently introduced into South Korea. As the causal pathogen has initially been attributed to Hyaloperonospora parasitica (syn. Peronospora parasitica), which was thought to affect various Brassicaceae, but is, in fact, restricted to Capsella bursa-pastoris, the identity of this pathogen remains uncertain. In this study, morphological and phylogenetic data revealed that maca downy mildew is unrelated to any species of Hyaloperonospora and instead belongs to the previously monotypic genus Perofascia. It differs markedly from the type species, Perofascia lepidii, and consequently Perofascia macaicola sp. nov. is described and illustrated here. Considering the quick expansion of cultivated land with maca, quarantine measures for this pathogen might be appropriate for hindering the spread of the disease through the international trade of maca.