Harpin Protein Influence on Fruit Quality Attributes, Ethylene, Respiration, and Minerals in Apples

The competitive global fruit market mandates production of apples with high quality attributes, particularly fruit color. Harpin Protein (Messenger®) is shown to trigger resistance to blue mold in apples, but limited information can be found on the effect of this compound on fruit quality. In this study, the impact of Harpin protein on quality attributes of four apple cultivars was studied. “Red Spur Delicious” apple fruit from trees receiving Harpin protein had significantly (about 23%) better color, earlier ethylene evolution, and higher respiration than those from untreated control trees, while their firmness was not adversely affected. Application of Harpin protein on “Red Chief Delicious” apple improved fruit color and increased fruit size in two locations, and advanced starch degradation pattern in one orchard but reduced fruit firmness in one location. Harpin protein tended (but not significantly) to improve fruit color in “Jonathan” and “Early Spur Rome” but reduced fruit size in “Jonathan” apples. Messenger® increased fruit percentage dry weight and Fe but decreased fruit Ca, Mg, K, and Zn. Improving apple fruit color by Harpin protein could have major impacts on apple industry and warrants further study.