Correlation Among Criteria for Evaluating Damages on Varieties of Sweet Potatoes by Cylas formicarius (F.)

Eight sweet potato varieties (including Fushu 8, Jinshan 57, Quanshu 12, etc.) of varied qualities were used for comparison in this study. For 3 consecutive years, they were planted with a randomized block design and grown at a same location, where a severe Cylas formicarius (F.) infestation existed. The damage index, tuber yield reduction and infection rate on the sweet potato stalks were monitored and confirmed prior to harvesting. Variance and correlation analyses were conducted along with tests on plant qualities. The results showed that the damage index rated the cultivars in the order of Jinshan 57 > Fushu 8 > Guangzhou 87 > Quanshu 12 > Fushu 88 > Fushu 90 > Fushu 9 > Fushu 2. Jinshan 57 suffered the most serious harm among all, and its tuber yield reduction was also among the greatest. Overall, Jinshan 57 and Fushu 8 encountered the heaviest damages by the infestation, while Fushu 2 the least. All 3 selected evaluation criteria showed extremely significant differences in the years of the survey. The damage index had the highest correlation coefficient with the tuber yield reduction, followed by the stalk infection rate, while that between the stalk infection and the tuber yield reduction rates the lowest. The statistical analysis suggested that those observations correlated significantly with the annual precipitation in the area, and that continued drought was the most important factor causing the outbreak of C. formicarius (F.) in a large area. In addition, a significant correlation was found between the nutritional quality and the damage index of the sweet potatoes due to C. formicarius (F.) infestation.