Effect Of Shade Netting And Bordeaux Liquid Spray On Sunburn And Physiological Characteristics Of Malus Spectabilis ‘Duojiao’ Leaves

Malus spectabilis’Duojiao’is a yellow leaf mutant that changes color dynamically as it grows.Its leaf color varies after germination,going from yellow red to yellow,yellow green,light green imbedded dark green plaque,and finally dark green,with a high ornamental value.The young leaves in the yellow stage began to develop leaf burning phenomenon as the light intensity and temperature progressively increased in late May,affecting the growth and ornamental leaves of Malus spectabilis’Duojiao’to some extent.Shade is the main measure to prevent leaf burning.However,the physiological changes and degree of Malus spectabilis shade have not been reported,so it is necessary to study a series of physiological traits such as photosynthetic characteristics after shade.In order to achieve the goal of preventing sunburn while maintaining its maximum ornamental properties,potted grafted seedlings of Malus spectabilis’Duojiao’and Malus spectabilis’Riversii’（CK）were treated with shade netting.The field plants Malus spectabilis’Duojiao’were treated with Bordeaux liquid spray.The preliminary study investigated the effects of different gradients of shade net and Bordeaux solution on the physiological traits of yellow leaves and leaf sunburn injury of’Duojiao’,and explored the measures to protect the healthy growth of the tree,maintain its maximum ornamental properties and improve the economic efficiency,and provided theoretical basis and technical support for the research on the molecular mechanism of leaf color variation and leaf color re-greening.This study will provide the theoretical basis and technical support for the research on leaf color variation and leaf re-greening.The main results are as follows:（1）After 30 days of shade netting,both gradient treatments resulted in a significant increase in the relative chlorophyll content of polygamous yellow leaves,with the relative chlorophyll content of the upper yellow leaves of Malus spectabilis with single and double shade nets increasing by 62.16%and 62.41%,respectively,compared to the control.The contents of P_n,Gs,Φ_PSII,F_v/F_mresistance enzymes and most minerals as well as soluble proteins in the leaves of Malus spectabilis’Duojiao’were significantly increased by single-layer shade net at the right time,and showed a trend of increasing and then slowly decreasing over time,but all of them were always higher than the control;C_i,T_rand MDA were significantly decreased,and showed a trend of decreasing and then slowly increasing over time,but all of them were always lower than the control.Although the double-layer shade net increased the chlorophyll of yellow leaves of Malus spectabilis’Duojiao’,P_n,G_s,Φ_PSII,and F_v/F_mgradually decreased;C_i,T_r,and MDA gradually increased.After 90 days of shading,the tree nutritional growth of the plants was inhibited to some extent,and the deeper the shading,the more serious the inhibition was.The growth of plant height and new shoot length were lower than that of the control,and the leaf area of plants treated with single-layer shade net was higher than that of the control and double-layer shade net.The combined indexes indicated that the single-layer shade net was more effective in moderate and moderate shade,and no leaf sunburn occurred.（2）After spraying the field plants with Bordeaux mixture,all three treatments significantly increased the chlorophyll content of’Duojiao’yellow leafs,increased by about4-fold,the P_n,G_s,Φ_PSII,F_v/F_mand resistance enzymes of the yellow leaves of Malus spectabilis’Duojiao’were significantly improved,increased by about 3-4 times,C_i,T_rand MDA were significantly reduced,1-2 times lower;The soluble protein content of’Duojiao’yellow leaves was significantly increased.（3）The three post-treatments of Bordeaux mixture significantly reduced the leaf burning rate and leaf burning index of yellow leaf Malus spectabilis,20 days after spraying,the leaf burn index of B0.5,B1 and B2 decreased by 58.27%,75.45%and 91.86%respectively compared with CK,all were significantly different from CK.The overall lime multiple treatment of the spray treatment has the best effect on preventing sunburn in the leaves,followed by equal treatment.