Potentiation of Resistance to Penicillium Spp. In Valencia Sweet Orange Through Use of Salicylic Acid and Methyl Jasmonate

Abstract

Citrus green and blue moulds cause postharvest losses worldwide. Therefore, the potential of preharvest foliar application of salicylic acid (SA) and methyl Jasmonate (MeJ) was investigated to control infection of Penicillium spp. An aqueous solution containing different concentrations of SA (3, 6, 9 mM) or MeJ (3, 4, 5 mM) and ‘Tween 80’ (0.05%) as a surfactant were sprayed onto whole trees seven days before harvest. Among the treatments, the pre-harvest spray of SA (9 mM or MeJ 5 mM) showed good efficacy reducing colony growth, wound rotting (rotting of peel around the wound and spore mass density of Penicillium spp. when compared with control. A pre-harvest spray of SA (9 mM) reduced colony growth by 71.02% and 68.69% on fruit inoculated with P. digitatum and P. italicum, respectively. The activity of fruit softening enzymes markedly increased following fungal infection. The decay in the fruit was found to be associated with the upregulation of activities of exopolygalacturonase (exo-PG), endopolygalacturonase (endo-PG) and Endo-1,4-ß-D-glucanase (e-gase). However, in un-inoculated fruit, negligible enzyme activity was observed. Contrarily the SA-treated fruit showed less activity of exo-PG, endo-PG and e-gase enzymes. These findings clued to develop natural control of Penicillium spp through use of organic elicitors in sweet orange fruit.