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.
ABSTRACT
Ultrasound, which refers to frequencies above the audible limit of human hearing, is a candidate for inducing resistance to pathogens in plants. We revealed that aerial ultrasound of 40.5 kHz could induce disease resistance in tomatoes and rice when the plants were irradiated with ultrasound of ca. 100 dB for 2 weeks during nursery season and reduced the incidence of Fusarium wilt and blast diseases, respectively, when plants were inoculated with pathogen 0 or 1 week after terminating irradiation. Disease control efficacy was also observed with ultrasound at frequencies of 19.8 and 28.9 kHz. However, cabbage yellows and powdery mildew on lettuce were not suppressed by ultrasound irradiation. No significant positive or negative effect on growth was observed in tomato and rice plants. RT-qPCR showed that the expression of PR1a involved in the salicylic acid (SA) signaling pathway was upregulated in the ultrasound-irradiated tomato.
