Combination of Ultraviolet-C Irradiation and Biocontrol Treatments to Control Decay Caused by Penicillium digitatum in 'Washington Navel' Orange Fruit

The combination of the yeast Candida oleophila strain '13L' with ultraviolet-C irradiation evidenced a synergistic effect in reducing A digitatum mould and only 11% of the artificially inoculated wounds were infected. Adversely, when the bacteria Bacillus subtilis strain 'B160' was combined with ultraviolet-C irradiation no synergistic effect was achieved. By using only yeast, bacteria or ultraviolet-C treatments the decay percentage was reduced by 79.6, 55 and 75%, respectively. The phytoalexin scoparone accumulation was high in all treatments where UV-C was applied but the highest values were found when combined with the yeast. Population growth of bacteria in vivo was halved when fruit was irradiated, whereas direct irradiation of bacteria did not affect their growth in vitro. An inhibitory effect of the phytoalexin toward the bacteria is suggested as the reason for the growth inhibition in vivo when the bacterial treatment was combined with UV-C irradiation.