Effects of Shading on Fruit Quality and Physiological Characteristics of 'Stevens’ Holly during the Color Transformation Period

To investigate the effects of different light intensities on the physiological characteristics of holly fruit during the color transformation period,an experiment was conducted using'Stevens’ holly as plant material.Four treatments were applied:full sunlight(CK)and three shading gradients- 35%(Z1),55%(Z2)and 75%(Z3)to explore the influence of shading on fruit appearance quality and physiological metabolism.The results showed that shading significantly inhibited the growth and development of 'Stevens’ holly fruits,with shading intensity and duration.Severe shading(Z3)significantly reduced fruit longitudinal diameter,transverse diameter,and single fruit weight,and led to an abnormal increase in fruit firmness,while mild shading(Z1 and Z2)had no significant effects. Shading delayed the fruit color-turning process;Z2 and Z3 treatments showed chlorophyll degradation and reduced the contents of carotenoids,anthocyanins,total phenols,and flavonoids.In contrast,35% shading(Z1)significantly increased soluble sugar and soluble protein contents.As fruit development progressed,Z2 and Z3 treatments significantly increased malondialdehyde(MDA)content and induced higher activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT).Using principal component analysis combined with membership function comprehensive evaluation,35% shading was identified as the optimal light condition for fruit development during the color-turning period of 'Stevens’ holly.