Effects of pre‐ and post‐treatment with ethephon on gum formation of peach gummosis caused by Lasiodiplodia theobromae

Peach gummosis, caused by Botryosphaeria spp. fungi, is the process of gum accumulation and exudation in plants. Ethephon (2‐chloroethylphosphonic acid) has profound effects on plants, including enhanced production of secondary metabolites and regulation of plant diseases. This study investigates the effects of application of ethephon before and after inoculation with Lasiodiplodia theobromae on gum formation. Gum formation was promoted by ethephon treatment prior to pathogen inoculation, but inhibited by ethephon applied after the pathogen. The inhibitory effect was counteracted by 1‐methylcyclopropane, which is an ethylene signal inhibitor. 1‐methylcyclopropane also promoted gum formation. Exposure of three isolates of Botryosphaeria to ethephon inhibited mycelial growth. Both treatment methods increased the sugar content at 12 and 24 h post‐inoculation (hpi). However, the sucrose, glucose and fructose contents were significantly higher in shoots with ethephon post‐treatment (application of ethephon after the pathogen inoculation) than those in shoots with ethephon pre‐treatment (application of ethephon prior to pathogen inoculation) at 48 and 72 hpi. The expression of two putative senescence‐related genes, SEN2 and SEN4, were significantly enhanced in pre‐ and post‐treated shoots with ethephon at 24, 48 and 72 hpi. Ethephon application also up‐regulated expression of the pathogenesis‐related protein PR4 while down‐regulating PR1a and PR10. The results show that ethephon has a dual function in regulating gum formation by affecting both the peach shoots and the pathogen.