Methyl jasmonate and acibenzolar-S-methyl protect cut Freesia hybrida inflorescences against Botrytis cinerea, but do not act synergistically

Methyl jasmonate (MeJA) and acibenzolar-S-methyl (ASM), two potential elicitors which activate plant defence responses, were tested on inflorescences of Freesia hybrida to suppress petal-specking caused by Botrytis cinerea. Compared to the untreated controls, MeJA applied as a vapour, pulse, or spray to freesia 'Cote d'Azur' inflorescences significantly reduced disease severity scores, lesion numbers, and lesion diameters on attached petals, and lesion diameters in a detached petal bioassay. ASM alone, at 143 mu M, provided a degree of protection to freesia inflorescences by significantly reducing disease severity scores, lesion numbers, and lesion diameters compared to the untreated controls. However, no additive effect was observed for combined treatments with MeJA and ASM. Polyphenol oxidase (PPO) activities in 0.1 mu l l(-1) MeJA-treated inflorescences, at 24 h and 36 h post-treatment, were 2.7- and 2.0-fold higher, respectively, compared to the untreated controls. In contrast, phenylalanine ammonia-lyase (PAL) activity in 0.1 mu l l(-1) MeJA-treated inflorescences was suppressed after 36 h, 48 h, and 72 h of incubation compared to PAL activities in the untreated control flowers.