Management of citrus blue and green moulds through application of organic elicitors

Abstract

The present studies aimed to develop control of citrus green and blue moulds caused by Penicillium digitatum and P. italicum, respectively, using elicitors as an alternate to synthetic chemicals. The dose-responsive toxicity of two organic elicitors was evaluated through a series of in vitro and in vivo experiments including pre- and postharvest application of different concentrations of salicylic acid (SA) or methyl jasmonate (MeJ) to ‘Lane Late’ sweet orange fruit for resistance induction. In in vitro experiments, SA significantly inhibited the radial growth, sporulation and spore germination of both Penicillium spp. compared to MeJ and control. SA (≥6 mM) showed direct fungitoxic effects and completely inhibited the radial growth, sporulation and conidial germination of both the pathogens. MeJ showed only a suppressive effect on fungal propagules and exhibited slightly better efficacy at concentrations ≥4 mM. A pre-harvest spray application of 8 mM SA or 3 mM MeJ to ‘Lane Late’ orange proved to be effective in reducing colony/lesion diameter, wound rotting and spore mass density of P. digitatum in contrast to postharvest treatment. We believe this is the first report demonstrating the efficacy of two organic elicitors in controlling the green mould in sweet orange. The present studies provide valuable information on standardization of minimum inhibitory concentrations (MICs) and pre- and postharvest treatment of sweet orange fruit with natural organic elicitors to induce resistance against postharvest pathogens.