Effects of Shading Stress on Qualities of Purple Sweetpotato Storage Roots

【Objective】 The study is to elucidate the effects of shading stress on root qualities of different genotypes purple-freshed sweetpotato.【Method】 Using Jishu18 and Ayamuraski as materials,the plants were shaded with nets which had 40%,70% transmittance of natural light at the root expanding peak period(50-100 d after transplantion),and the natural light was used as the control.Dry matter,starch content,amylose and amylopection content,starch accumulation ratio,soluble sugar content,protein content,the parameters of viscosity and anthocyanidin content of tuber root were determined.【Result】 Results indicated that dry matter,total starch content and starch accumulation rate in the root of purple-freshed sweetpotato decreased significantly compared with the control under shading treatments.Shading treatments not only significantly increased amylose content and the ratio between amylose and amylopectin,but also significantly decreased peak viscosity,break down,set back and pasting temperature of Jishu18.However,the above-mentioned starch qualities of Ayamuraski were against to those of Jishu18.Soluble sugar and soluble protein increased significantly accompaned by rising of shading degree in two cultivars.In addition,anthocyanidin content and accumulation rate declined significantly under shading treatments,compared with Ayamuraski,the response to stress of Jishu18 was more sensitive.Researches showed that shading treatments changed root qualities of purple-freshed sweetpotao and displayed difference between varieties.【Conclusion】 Shading treatments can significantly decrease dry matter,starch content and starch accumulation ratio,anthocyanidin content and anthocyanidin accumulation in tuber root of purple-freshed sweetpotato,while the quality of root starch varied in the different sweetpotato varities under shading treatments.