Blue mold rot, caused by Penicillium expansum, is one of the most economically important post-harvest diseases of apple worldwide. The goals of this study were threefold: to evaluate the diversity of P. expansum isolates for mycelial growth, spore production and lesion diameter on apples; to estimate the effects of cold-storage facility conditions on P. expansum population structure; and to investigate the efficacy of three essential oils against P. expansum. The results showed that storage facilities applying fungicides and storing diverse fruit species selected for P. expansum isolates with a larger lesion diameter on apples. In addition, application of fungicides and diversification in stored fruit species significantly select for P. expansum isolates with higher levels of mycelial growth and spore production, respectively. Moreover, the diversity of host species of stored fruit accounted for 38% of the variability observed between storage facilities for the measured fitness parameters in P. expansum isolates and had a stronger effect on P. expansum population structure than fungicide treatment. Essential oils from Mentha pulegium and Syzygium aromaticum significantly decreased mycelial growth and spore production of P. expansum isolates in vitro. Mentha pulegium essential oil also significantly decreased the size of lesions associated with the blue mold rot of apples. Reducing the diversity of stored host species and applying M. pulegium essential oil may be useful in counter-selecting for aggressive P. expansum isolates and reducing losses due to blue mold rot during fruit storage.
