Hexanoic acid provides long-lasting protection in ‘Fortune’ mandarin against Alternaria alternata

• Single application of hexanoic acid protects up to 2 months against Alternaria alternata.
• Long lasting protection is mediated by the increase of PGIP and phenolic compounds.
• After second inoculation treated plants showed lower lesions and infected leaves.

Alternaria brown spot disease is a serious disease in mandarins and their hybrids without effective disease control measures. In recent years, induced plant resistance has been studied as an alternative to classical pesticides, but few studies on the effectiveness of these products and their long-lasting effects in woody crops have been performed. After two inoculations with Alternaria alternata, citrus plants that were treated with hexanoic acid showed enhanced resistance, displaying lower levels of disease incidence associated with an activation of the jasmonic acid pathway, the accumulation of phenolic compounds and the expression of defensive genes, such as polygalacturonase-inhibiting proteins.