Rhodosporidium paludigenum induced resistance in Ponkan mandarin against Penicillium digitatum requires ethylene-dependent signaling pathway

• Rhodosporidium paludigenum induced resistance against Penicillium digitatum in mandarin orange.
• 1-MCP pre-fumigation destroyed natural and yeast-activated protection in the fruit.
• ETR1, ETR2, ETR3, ETR4 and ERF genes were yeast and 1-MCP responsive.
• The induction of defensive genes by R. paludigenum was abolished by 1-MCP.

This work determined if the ethylene dependent signal pathway was required for antagonist-mediated fruit defense mechanisms through investigation of disease resistance against Penicillium digitatum in Ponkan mandarin induced by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, and Rhodosporidium paludigenum. Blocking ethylene perception with 1-MCP resulted in an increase in ACS1, ACS2 and ACO expression, and consequently an increase in ethylene production during mechanical wounding and resistance induction. The expression of the ethylene receptors ETR1, ETR2 and ETR4 as well as ethylene response factor (ERF) were observed with similar responses to yeast and 1-MCP stimuli, with ETR3 mRNA accumulation being the most sensitive to yeast application while ERS1 was the least sensitive. When applied at concentrations greater than 500 nL L−1, 1-MCP pre-fumigation significantly reduced the fruit's natural protection and R. paludigenum induced disease resistance to Penicillium decay, indicating that ethylene perception was involved in inducting disease resistance. Moreover, expression of the defensive genes CHI, β-1,3-glucanase, PAL and CIN up-regulated by yeast was inhibited to different degrees by the 1-MCP pre-treatment. This study provides evidence that the biocontrol yeast R. paludigenum increased disease resistance in Ponkan mandarin against P. digitatum infection due to ethylene and signaling pathway dependent mechanisms.