Differential susceptibility of Morettini pears to blue mold caused by Penicillium expansum

Pear fruit (Pyrus communis L. cv Beurre Precoce Morettini) developing on the outside of canopy and exposed to sunlight acquires a bright redness on the exposed side, compared to the green peel fruit that develop within the canopy. At harvest, the main physicochemical parameters of the red and green side of the fruit, including firmness, brix and titratable acidity, were similar in pears harvested at the same day and stage of maturity. However, it was observed that fruits with a red side or that mostly green showed a different response to biotic stress, namely to pathogenic fungi attack. Actually, after 7 days under shelf-life conditions, red fruits demonstrated to be more resistant than green ones when challenged with a postharvest Penicillium expansum inoculation. Significant differences were observed in antioxidant activity and total phenolic compounds between both sides of the fruits. Several polyphenols related to mechanisms of induced resistance against fungal plant pathogens were identified in the extracts, such as catechin, quercetin, quinic acid or caffeoylquinic acid. These results suggest that the accumulation of phenolic compounds triggered by sun exposure may be one of the mechanisms responsible for the increased resistance of red-skinned Morettini pears.