A new species of Bremia from the traditional crop Carthamus tinctorius from Iran

Bremia species cause downy mildew disease of Asteraceae, in particular in the subfamilies Cichorioideae and Carduoideae. The most notorious species is B. lactucae, which causes lettuce downy mildew. Previously, it was often assumed that this species causes disease on dozens of different host genera, but recent phylogenetic and morphological studies have shown that most species of Bremia are highly host specific and that B. lactucae might be mostly limited to Lactuca sativa and L. serriola. As a first step towards investigating the diversity of Bremia in Iran, ten fresh samples of downy mildew from Carthamus tinctorius and Sonchus asper were collected in 2017 to 2018 from various regions of Ahvaz in the southwest of Iran and subjected to morphological and molecular characterisation. Phylogenetic analyses based on cox2 sequences of mtDNA indicated that these samples represent two sister species of Bremia, B. milovtzovae sp. nov. and B. sonchi, causal agents of downy mildew on C. tinctorius and S. asper, respectively. Morphologically, B. milovtzovae sp. nov. can be readily distinguished from its sister species, B. sonchi, by more elongated conidia and shorter conidiophores.