The Correlation of Cracking Fruits Types and Peel Structure between ‘Washington’ and ‘Bonanza’ Navel Oranges

Fruit cracking is a serious pre-harvest physiological disorder commonly found in many navel orange orchards and results in lots of loss in commercial cultivation.The two navel orange species,Washington(Citrus sinensis Osbeck Washington)and Bonanza(Citrus sinensis Osbeck Skaggs Bonanza)navel orange from Anyuan and Xunwu County of Jiangxi Province and Zhongshan City of Guangdong Province,were used in this study.Obvious differences existed in flavedo,albedo and cell wall ultrastructure of healthy peel among different navel orange cultivars in which there were different cracking fruit types.Washington and Bonanza navel orange are high cracking fruit cultivars.In the contrary,most cracking fruits of Washington navel orange begins from albedo.Both of them had intact-structural flavedo,albedo,middle lamella(ML)and primary wall(PW).The flavedo of Bonanza navel orange was smaller,thinner and waved greatness,had bigger interspaces between cells than Washington navel orange,while the albedo of Bonanza navel orange was more regular than that of Washington navel orange.The albedo of Washington navel orange had bigger interspaces between cells,poorer spongy layer network and middle lamella than that of Bonanza navel orange.