Mutations found in the Asc1 gene that confer susceptibility to the AAL-toxin in ancestral tomatoes from Peru and Mexico

Abstract

Tomato susceptibility/resistance to stem canker disease caused by Alternaria alternata f. sp. lycopersici and its pathogenic factor AAL-toxin is determined by the presence of the Asc1 gene. Several cultivars of commercial tomato (Solanum lycopersicum var. lycopersicum, SLL) are reported to have a mutation in Asc1, resulting in their susceptibility to AAL-toxin. We evaluated 119 ancestral tomato accessions including S. pimpinellifolium (SP), S. lycopersicum var. cerasiforme (SLC) and S. lycopersicum var. lycopersicum “jitomate criollo” (SLJ) for AAL-toxin susceptibility. Three accessions, SP PER018805, SLC PER018894, and SLJ M5-3, were susceptible to AAL-toxin. SLC PER018894 and SLJ M5-3 had a two-nucleotide deletion (nt 854_855del) in Asc1 identical to that found in SLL cv. Aichi-first. Another mutation (nt 931_932insT) that may confer AAL-toxin susceptibility was identified in SP PER018805. In the phylogenetic tree based on the 18 COSII sequences, a clade (S3) is composed of SP, including the AAL-toxin susceptible PER018805, and SLC. AAL-toxin susceptible SLC PER018894 and SLJ M5-3 were in Clade S2 with SLL cultivars. As SLC is thought to be the ancestor of SLL, and SLJ is an intermediate tomato between SLC and SLL, Asc1s with/without the mutation seem to have been inherited throughout the history of tomato domestication and breeding.

La susceptibilidad/resistencia del tomate a la enfermedad del cancro del tallo causada por Alternaria alternata f. sp. lycopersici y su factor patógeno AAL-toxina está determinada por la presencia del gen Asc1. Se ha informado que varios cultivares de tomate comercial (Solanum lycopersicum var. lycopersicum, SLL) tienen una mutación en Asc1, lo que resulta en su susceptibilidad a la toxina AAL. Se evaluaron 119 accesiones ancestrales de tomate, incluyendo S. pimpinellifolium (SP), S. lycopersicum var. cerasiforme (SLC) y S. lycopersicum var. lycopersicum "jitomate criollo" (SLJ) para la susceptibilidad a la toxina AAL. Tres accesiones, SP PER018805, SLC PER018894 y SLJ M5-3, fueron susceptibles a la toxina AAL. SLC PER018894 y SLJ M5-3 tenían una deleción de dos nucleótidos (nt 854_855del) en Asc1 idéntica a la encontrada en SLL cv. Aichi-first. En SP PER018805 se identificó otra mutación (nt 931_932insT) que podría conferir susceptibilidad a la toxina AAL. En el árbol filogenético basado en las 18 secuencias COSII, un clado (S3) está compuesto por SP, incluido el PER018805 susceptible a la toxina AAL, y SLC. SLC PER018894, susceptible a la toxina AAL, y SLJ M5-3 se encontraban en el clado S2 con cultivares SLL. Como se cree que SLC es el ancestro de SLL, y SLJ es un tomate intermedio entre SLC y SLL, Asc1 con/sin la mutación parece haberse heredado a lo largo de la historia de la domesticación y mejora del tomate.