Effects of Genotype and Planting Density on Agronomic Traits and Storage Root of Sweetpotato

The effects ol different genotypes and planting densities on main agronomic traits, storage root traits and yield were studied with 6 high-quality sweetpotato varieties as study objects by 2-factor completely random design. The results showed that there were significant differences in stem diameter, length of the longest vine and top/root （T/R） between different genotypes, T/R differed significantly under dif- ferent planting densities, and number of basal branches decreased with planting density increasing. Genotype and genotype x density showed significant or very sig- nificant effects on fresh root yield per plant, dry matter content and fresh root yield per hectare, fresh root yield per plant gradually decreased with planting density in- creasing, while fresh root yield per hectare increased with planting density increas- ing. Numbers of storage roots in different sizes of the 6 sweetpotato cultivars all exhibited an order of number of large-sized storage roots〈number of medium-sized storage roots〈small-sized storage root; and there were very significant differences in ratio of large-sized storage roots between different genotypes. The number of large- sized storage roots, ratio of large-sized storage roots and number of commercial storage roots deceased with planting density increasing, while there were no signifi- cant differences in number of medium-sized storage roots, number of small-sized storage roots, ratio of medium-sized storage roots and ratio of small-sized storage roots between different densities. Correlation analysis showed that there was signifi- cant positive correlation between number of basal branches and fresh root yield per plant; dry matter content in storage roots was in significant positive correlation with stem diameter, and in significant negative correlation with length of the longest vine; fresh root yield per hectare was in significant positive correlation with fresh root yield per plant, and in very significant negative correlation with dry matter content; and ratio of large-sized storage roots was in very significant positive correlation with number of large-sized storage root and fresh root yield per plant, and in very sig- nificant negative correlation with ratio of medium-sized storage roots and ratio of small-sized storage roots. This experiment showed that under the planting density of 7.5×104 plants/hm2, the 6 sweetpotato cultivars all reached the highest numbers of commercial storage roots and fresh root yields per hectare.

Accumulation and Gene Expression of Anthocyanin in Storage Roots of Purple-Freshed Sweet Potato [Ipomoea batatas (L.) Lam] Under Weak Light Conditions

Anthocyanidin in plants, an important pigment, is of great interest to researchers, consumers, and commercial entities due to its physiological functions. Anthocyanin content and mRNA levels of anthocynin biosynthesis genes were investigated in storage root of different purple-fleshed sweet potatoes (PFSP) genotypes to understand the regulation mechanism of anthocyanin under weak light conditions. Anthocyanin content, its amount of accumulation, and the expression of CHS, DFR, F3H, GT, and ANS genes in the PFSP storage root under weak light conditions were studied. The results demonstrated that the anthocyanin content of the treatments was decreased and was obviously lower than that of the control until 30 days after shading in Ayamurasaki, while it was lower than that of the control from the beginning of shading in Jishu 18. Their accumulation rates of both treatmeants were lower than its control before 10-20 d of shading in Jishu 18, while those of Ayamurasaki weren't in their treatments. This indicated that Jishul 8 is more sensitive to light as compared to Ayamuraska. Under the different weak light conditions, mRNA levels for ibCHS, ibF3H, ibDFR, and ibANS were obviously decreased, while the expression of ibGT was increased. These results indicated that anthocyanin content was regulated by light at the mRNA levels and the enzymatic level in sweet potato. Therefore, the development dynamic response to anthocyanin content varied in different genotypes of PFSP, and mRNA levels of anthocyanin biosynthesis were inhibited under the weak light condition.

Sand Storage, Extending the Shelf-Life of Fresh Sweetpotato Roots for Home Consumption and Market Sales

Uni-modal rainfall pattern has long dry spell wherein sweetpotato is scarce, expensive but cheap at harvest. The crop is mostly consumed, processed or sold. Extending shelf-life of roots is crucial for Malawi and Northern Ghana as the crop has high value. Trials were conducted in the countries at the community level. In the dry season, temperature is cool in Malawi while warm in Ghana, but thru harmattan, the night is cool with low relative humidity. In Malawi, orange-fleshed sweetpotato Zondeni var., white and yellow types were assessed in three types of storage, Afghan ventilated pit store, storage in dry sand of pit-steps, and of a granary In Ghana, local moistened heap and sandbox were compared. In Malawi, weight losses were calculated relative to the quantity stored at start, it was not cumulative. At 1.5 months no significant difference was among treatments. By 3.5 months the pit-steps method emerged to be superior and continued to 6.5 months. Losses in granary were due to shriveling, in the pit-stepsdue to termites and rats, and in ventilated pit due to termites, rats and Java black rot. Sprouting was high in pit-steps, but it was simply removed and roots returned to storage. At 6.5 months, the beta-carotene of Zondeni roots was traceable. Farmers gained high price when selling them as roots were scarce. Women favored the pit-steps because it was manageable. In Ghana, the sandbox was superior to local moistened heap. Methods designed were suitable for home consumption, but will require modification for commercialization.