Dry Matter Production of Sweet Potato in True Seed Planting Culture

To clarify the reason of lower yield in true seed planting (TSP) culture than that of ordinary transplanting culture of stem cuttings, the top and storage root growrth were investigated among six populations in TSP culture and two cultivars in ordinary culture. There was a large variance in the yield among the TSP populations which differed in parental clones. Especially, one of the TSP populations showed a high yield similar to the high yielding cultivar. The difference in the dry matter production among the materials during the period from late August to middle October, which was major cause of the yield difference, was mainly affected from the difference in the leaf efficiency (total dry weight increase/mean leaf dry weight). Since its leaf efficiency tended to be higher in the materials with the higher storage root weight ratio (storage root dry weight/total dry weight) in the late August, a close correlation was observed between the storage root weight ratio in the late August and the yield among the materials. The present results indicated that, with the aid of some cultural practices used to improve early top growth in the TSP culture, we could expect as high a yield in the TSP culture as in the ordinary culture, by using an excellent TSP population. It was also suggested that there was a large difference in storage root sink potential among the TSP populations, and it mainly governed the leaf efficiency and dry matter production during later storage root bulking period and thus the yield.