Two plum (Prunus salicina Lindl.) cultivars ‘Black Splendor’ (BS) and ‘Royal Rosa’ (RR) were treated with
methyl jasmonate (MeJA) at 3 concentrations (0.5, 1.0 and 2.0 mM) along the on-tree fruit development:
63, 77 and 98 days after full blossom (DAFB). On a weekly basis, fruit samples were taken for measuring
fruit size and weight and parameters related to quality. Results revealed that MeJA was effective in
increasing fruit size and weight, the 0.5 mM being the most effective for BS cultivar and 2.0 mM for
RR. At harvest, those fruit treated with 0.5 mM MeJA had the highest firmness and colour Hue values.
Total acidity was also generally higher in MeJA-treated fruit than in controls, while the content of total
soluble solids remained unaffected. In addition, total phenolics and total antioxidant activity were found
at higher concentrations in 0.5 and 2.0 mM MeJA-treated than in control fruit over at last 3 weeks of fruit
development for BS and RR cultivars, respectively. Overall results suggest that MeJA could be a promising
preharvest tool to increase plum size and quality with enhanced bioactive compounds and antioxidant
activity, although the optimum concentration is cultivar dependent.