Multi-locus phylogeny and pathogenicity of Stemphylium species associated with legumes in Australia

Abstract

This study was initiated to elucidate the taxonomy and host range of Stemphylium species associated with leaf spot of faba bean in Australia. A three-locus phylogenetic analysis of 41 isolates collected from faba bean and other Fabaceae and Brassicaceae crops was constructed employing the internal transcribed spacers and the intervening 5.8S region of the nuclear ribosomal DNA, glyceraldehyde 3-phosphate dehydrogenase, and calmodulin sequences. The results indicated that more than one Stemphylium species occurs on faba bean (Vicia faba), chickpea (Cicer arientinum), lentil (Lens culinaris), and narrow-leafed lupin (Lupinus angustifolius) in Australia. Five Stemphylium species (S. astragali, S. beticola, S. eturmiunum, S. simmonsii, and S. vesicarium) were found associated with legume crops, of which S. astragali is a new report for Australia. Although isolates obtained from faba bean were retrieved within S. eturmiunum and S. vesicarium clades, those pathogenic to faba bean belonged to S. eturmiunum, a species not previously reported on faba bean. Interestingly, some S. eturmiunum isolates obtained from faba bean and other legumes were unable to infect faba bean, which indicated the potential presence of formae speciales within this species. The ability of S. eturmiunum isolates to cause plant death in susceptible faba bean varieties within only a few days emphasises the need for incorporation of Stemphylium blight resistance into faba bean breeding programs. Also, further research into the biology and epidemiology of the disease is warranted.