Effects Of Plastic Tunnel Culture On Growth And Quality Of 'Cuiguan' Pear

The cultivar'Cuiguan'pear belongs to sand pear (Pyrus pyrifolia Nakai).The fruit is well known by its strong adaptability and high quality, so it was popularized throughout Zhejiang province rapidly in these years. Plastic tunnel culture has some good characteristics, such as regulating fruit maturation, preventing natural disasters and improving economic benefit, so it spread quickly along coastal area all over China. However, studies showed that poor fruit quality was found when cultivated in plastic tunnels. To solve this problem, The method of plastic tunnels culture were used in 'Cuiguan' pears for successive two years, to observe the effects of this kind of culture on relative physiology and the quality composition of pear fruits, and reflecting films were also used in plastic tunnels to study the saccharometabolism and quality changes in pear fruits. This study provided scientific guidance for producing high quality of'Cuiguan'pears in plastic tunnels. The main results were as follows:The growth curve of'Cuiguan' pear fruits was S-shaped. Compared to the pears grown in the open field (controls), the diameter, length and weight of fruits during the late stage of development were less than the ones in plastic tunnel, but the impact was not significant. In this experiment, the colorimeter was used for measuring the appearance color of'Cuiguan'pears. The results suggested that plastic tunnel culture could improve saturation (C) and decrease brightness (L*) of'Cuiguan'pears during the maturation stage. The'Cuiguan'pear fruits in plastic tunnel had smaller dots, of which the diameters and density were also lower than controls. However, there was no significant impact on fruit firmness. The proportion and content betweensugar and acid played an important role in fruit quality. The TSS was significantly lower but the contents of malic acid, citric acid, and total acids were higher than controls at harvest stage. Fructose, sorbitol, glucose and sucrose were the main soluble sugars in'Cuiguan'pear and they were decreased during plastic tunnel culture, especially sucrose. Sucrose increased rapidly in the last development stage of'Cuiguan'pear and the content in fruit cultivated in plastic tunnels was significantly lower than that of controls. The results showed SPS was the most significant enzyme which positively correlated with the accumulation ofsucrose (r=0.908** in plastic tunnel culture, r=0.858* in control) while the second key enzyme was NI (r=-0.739* in plastic tunnel culture, r=-0.467 in control). The other enzymes (SS and AI) had no so significant relationship with sucrose. Plastic tunnel culture could decrease the content of soluble sugars, especially sucrose, which was mainly by reducing the enzyme activity of SPS and enhancing the enzyme activity of NI.The next year, silvery reflecting films were laid in plastic tunnels where Cuiguan' ears were cultivated to improve light condition under the tree crown and photosynthesis of leaves. The changes of fruit color, sugar and acid contents and enzyme activities of Cuiguan' ears were examined once again. The results showed fruits treated with reflecting films had significantly higher TSS. The weight and firmness of fruits were also a little higher than those of controls, but they had few differences from controls. The treatment also changed the proportions of soluble sugars. All the four kinds of soluble sugars were higher than controls, especially sucrose content was significantly increased. Five enzymes related to the sucrose metabolism were tested in this study, of which the enzyme activities of SPS and NI were higher and lower than the controls, respectively. After treating with the reflecting films,the change of light qualitative might induce the phytochrome regulating on the sucrose metabolizing enzymes, and lead to the changes of these enzyme activities, e.g.,SPS and NI.In conclusion, plastic tunnel culture improved the fruit appearance of'Cuiguan' ears to a certain extent while it raised the organic acid content and reduced the soluble sugars content, especially sucrose content. Thus, the inner qualities of'Cuiguan'pears were affected. Laying reflecting films in plastic tunnel improved the light condition. As a result, the content of soluble sugars increased and the inner qualities of'Cuiguan'pear- improved.