The Study Of Effect Of Bagging On Formation And Development Of Fruit Skin Rust Of Huangguan Pear

The experiment has been conducted to study the influence of fruit bagging on various environmental and some bio-chemical factors, which have been long believed involved in formation of fruit rust, evaluate the effectiveness of bagging in reducing the risk of fruit rust, study the roles various factors play in process of rust formation, and analyze the relationship among various factors in promoting rust formation, further explore the mechanism of formation and development of fruit rust on the skin of huangguan pear.In assay, four types of bags were employed, by which pear fruit were bagging-treated on different development stages. At the same time, the treatment of spraying water into bag was made at three levels within five different periods of fruit development, which aimed at increasing and maintaining the humidity in bags. Through periodically measuring environmental factors and determining bio-chemical substances involved in forming of fruit rust, it showed that bagging has remarkable influence on the formation of fruit rust through altering micro-environment for fruit development and regulating physiological metabolism that are relevant. The results indicated that, with the date of bagging being delayed, the rust index shows downward tendency and that of fruit bagged 50-60days after full blossom was the lowest. On the whole, the effectiveness of single-layer bags in restricting rust formation is more distinct than that of double-layer bags. All spraying-water treatments can aggravate the formation of fruit rust at different degree.Three kinds of enzymes, POD,PPO and PAL, which are relevant to the metabolism of phenol compounds, were found to play important roles in forming rust on fruit skin. Their activity levels in fruit, especially on early stage of fruit development, are closely related to rust formation. It was also indicated that, compared with PPO, POD and PAL act more important roles in forming and developing of fruit rust. In addition, through the research that was concerned with the influence of adding humidity on the three enzymes' activity levels in fruit and their relationship with fruit rust formation, it can be presumably believed that environmental factors do not affect the formation and development of fruit rust by directly changing enzymes' activity levels in fruit. And most likely, they function as factors that activate the activity and development of cork cambium under fruit skin. While the alteration of these enzymes' activity levels in fruit is likely the physiological response to the rust development, rather than the direct consequence of environmental factors changing. The experiment results also indicated that the increase in content of the total pectin and the decrease of the cellulose content in fruit skin can enhance the ductility of its, by which the formation of fruit rust can be restricted significantly. In addition, it was discovered that both endogenous hormone and elements in fruit skin are involved in the process of formation and development of fruit rust. The results showed that the decrease in contents of endogenous IAA and Ca in fruit skin is closely related to the promotion of fruit rust formation. Finally, through scanning and observing cell tissue structure of fruit skin by using optical and electronic microscope, it showed that, the integral cuticle structure on fruit surface and the thick compact skin-cell tissue with solid structure, which fruit bagging-treated in appropriate bag on optimum time bears, can radically depress the risk of fruit rust. And this probably plays partly immanent roles in influencing the formation of fruit rust on the skin of huangguan pear.