Dr. Mattheis' principle area of investigation is postharvest physiology of apples, pears and cherries. Ongoing topics of research include assessment of various fruit physiological and quality factors as indicators of fruit harvest maturity, determination of appropriate maturity indices for new fruit varieties grown in the Pacific Northwest, characterization of fruit responses to stressful storage environments and identification of principle volatiles produced by fruit as indicators of physiological condition. Preharvest field research includes the study of apple and pear fruit blossom physiology.