| Summary: | Tomato susceptibility/resistance to stem canker disease caused by <i>Alternaria alternata</i> f. sp. <i>lycopersici</i> and its pathogenic factor AAL-toxin is determined by the presence of the <i>Asc1</i> gene. Several cultivars of commercial tomato (<i>Solanum lycopersicum</i> var. <i>lycopersicum</i>, <i>SLL</i>) are reported to have a mutation in <i>Asc1</i>, resulting in their susceptibility to AAL-toxin. We evaluated 119 ancestral tomato accessions including <i>S. pimpinellifolium</i> (<i>SP</i>), <i>S. lycopersicum</i> var. <i>cerasiforme</i> (<i>SLC</i>) and <i>S. lycopersicum</i> var. <i>lycopersicum</i> “jitomate criollo” (<i>SLJ</i>) for AAL-toxin susceptibility. Three accessions, <i>SP</i> PER018805, <i>SLC</i> PER018894, and <i>SLJ</i> M5-3, were susceptible to AAL-toxin. <i>SLC</i> PER018894 and <i>SLJ</i> M5-3 had a two-nucleotide deletion (nt 854_855del) in <i>Asc1</i> identical to that found in <i>SLL</i> cv. Aichi-first. Another mutation (nt 931_932insT) that may confer AAL-toxin susceptibility was identified in <i>SP</i> PER018805. In the phylogenetic tree based on the 18 COSII sequences, a clade (S3) is composed of <i>SP</i>, including the AAL-toxin susceptible PER018805, and <i>SLC</i>. AAL-toxin susceptible <i>SLC</i> PER018894 and <i>SLJ</i> M5-3 were in Clade S2 with <i>SLL</i> cultivars. As <i>SLC</i> is thought to be the ancestor of <i>SLL</i>, and <i>SLJ</i> is an intermediate tomato between <i>SLC</i> and <i>SLL</i>, <i>Asc1</i>s with/without the mutation seem to have been inherited throughout the history of tomato domestication and breeding.
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