Targeted Suppression of the Tomato Pathogen Alternaria alternata via Exogenous Application of Double-Stranded RNA

Alternaria blight, caused by fungi of the genus Alternaria, is one of the most common and damaging diseases affecting tomatoes, leading to significant yield losses. The intensive use of chemical fungicides faces the problems of pathogen resistance development and negative environmental impacts. This study investigated the possibility of using RNA interference technology based on exogenous double-stranded RNAs (dsRNAs) to protect tomatoes against the causal agent of early blight (EB), Alternaria alternata. Key genes of the pathogen A. alternata were selected as targets: Alt-a1 (a major allergen and virulence factor), TEF1a (translation elongation factor 1-alpha) and β-Tub (β-tubulin). Specific dsRNAs were synthesized in vitro and applied to tomato plants (Solanum lycopersicum L. cv. Micro-Tom) simultaneously with inoculation of A. alternata strain C7.24-T2-L-F1 spores. Visual assessment, measurement of chlorophyll A and B, and real-time quantitative PCR analysis showed that treatment with dsRNAs targeting the Alt-a1, TEF1a and β-Tub genes significantly suppressed infection development, reducing the amount of pathogen DNA in plant tissues by 7 to 27 times depending on the dsRNA type. The most effective was dsRNA to the Alt-a1 gene. Thus, the obtained results demonstrate the promise of spray-induced gene silencing (SIGS) as a strategy for protecting tomato plants against the pathogen A. alternata.