Effects of cooling measures on 'Nijisseiki' pear (Pyrus pyrifolia) tree growth and fruit quality in the hot climate

Through the effects of global warming, rising temperatures is becoming an increasing problem for fruit production. Pyrus pyrifolia 'Nijisseiki' is a famous Japanese pear cultivar that was introduced to East China in the 1930s. However, 'Nijisseiki' pears showed great inadaptability to the cultivation environment, and do not provide good yield when grown in East China where temperatures are higher than Japan. Here, we introduced two cooling measures, mist spray and shade cloth treatments, to test for whether they can mitigate heat-induced damage to 'Nijisseiki' pear. This study was conducted in summer of 2013, 2014 and 2015 at Yangzhou (Jiangsu, China). A typical weather model was established to evaluate the cooling effect of each treatment. The results showed both treatments were maintaining regular levels of the photosynthetic system utilization and antioxidant enzyme activity, and reducing damage from ROS compounds. The shade cloth treatment decreased excessive growth, promoted spur growth and higher SPAD value but delayed its maturity than those treated with mist spray. Both treatments increases yields per tree. Considering the cost, shade cloth treatment is the reasonable cooling measure on 'Nijisseiki' pears in Yangzhou. In addition, eight PpyHsfs that showed gene expression level changes based on temperature. And HsfA3b was the most sensitive to high temperature.