A re-examination of the phylogenetic relationship between the causal agents of carrot black rot, Alternaria radicina and A-carotiincultae

The phylogenetic relationship between Alternaria radicina and A. carotiincultae vas re-examined based on morphology, sequence analysis of rDNA (ITS and mitochondrial small subunit [mtSSU]), protein coding genes (actin [ACT], beta-tubulin chitin synthase [CHS], translation elongation Factor [EF-1a], Alternaria, allergen al [Alt al], and glyceraldehyde-3-phosphate dehydrogenase [gpd]), and RAPD and ISSR analysis of total genomic DNA Although some morphological characters overlapped to a degree, with A. radicina isolates expressing moderate variation and A. carotiincultae isolates being highly uniform, A. carotiincultae Could be differentiated from A. radicina based on significantly greater growth rate on potato dextrose agar (PDA) or acidified PDA (APDA) and average number of transverse septa per conidium. Sequence of rDNA and MO protein coding genes, ACT and CHS, were invariant between species. However polymorphism with the EF-1a, beta-tubulin, and Alt a1 gene strictly separated the population of A. radicina and A. carotiincultae as distinct lineages, as did RAPD and ISSR analysis. The polymorphic gpd gene did not. Strictly separate the two species. However isolates of A. radicina encompassed several haplotypes, one of which was the exclusive haplotype possessed by A. carotiincultae isolates, Suggesting evidence of incomplete lineage sorting. The results suggest chat A. carotiincultae is closely related to A. radicina but is a recently divergent and distinct lineage, which supports its status as a separate species.