Inheritance of low pasting temperature in sweetpotato starch and the dosage effect of wild-type alleles

Polyploid QTL-seq revealed multiple QTLs controlling steamed tuber texture and starch gelatinization temperature in sweetpotato

Sweetpotato (Ipomoea batatas) includes diverse cultivars with flesh textures ranging from dry to moist. Moist-fleshed cultivars often contain starch with a lower gelatinization temperature (GT). To elucidate the genetic determinants of flesh texture and starch GT, we conducted a QTL analysis using F1 progenies obtained from a cross between dry-fleshed and moist-fleshed cultivars, 'Benikomachi' (BK) and 'Amahazuki' (AH), by using an updated polyploid QTL-seq pipeline. Flesh texture was assessed based on the wet area ratio (WAR) observed on the cut surface of steamed tubers, as progenies with dry and moist flesh exhibited low and high WAR values, respectively, demonstrating a strong correlation. Three QTLs were found to regulate the WAR. Notably, two AH-derived alleles at 4.30 Mb on Itr_chr05 and 21.01 Mb on Itr_chr07, along with a BK-derived allele at 2.89 Mb on Itr_chr15, were associated with increased WAR. Starch GT, which displayed no correlation with either flesh texture or WAR, was distinctly influenced by two QTLs: a GT-increasing BK-derived allele at 1.74 Mb on Itr_chr05 and a GT-decreasing AH-derived allele at 30.16 Mb on Itr_chr12. Consequently, we developed DNA markers linked to WAR, offering a promising avenue for the targeted breeding of sweetpotato with the desired flesh textures.

Easy to Swallow Rice Cake as a Carbohydrate Source during Endurance Exercise Suppressed Feelings of Thirst and Hunger without Changing Exercise Performance

The present guidelines for sports nutrition recommend relatively higher doses of carbohydrates (CHO) for endurance exercise. There is a need for novel food products that are solid but easy to swallow and supply a large dose of CHO without gastrointestinal distress (ingesting a large amount of sugar solution may cause gastrointestinal distress because of its high osmolality). We prepared a modified rice cake (SPRC, sweet potato rice cake) and assessed its properties in swallowing and mastication; we also assessed the availability of this modified rice cake as a CHO source during endurance exercise. The number of chewing strokes with the SPRC tended to be lower compared to glutinous rice cakes. The exercise protocol consisted of 1 h at 80% VO_2max plus a continuous time trial. The subjects were administered a commercially available jelly drink (CHO gel) or SPRC at 0 and 30 min during exercise and immediately after completing the time trial. Heart rate, oxygen consumption, blood glucose elevation, and the rate of perceived exertion did not differ among the trials during exercise. However, the visual analog scale rating revealed that SPRC significantly suppressed hunger and sweetness ratings (p<0.05) and tended to suppress thirst ratings (p<0.10) during exercise. The palatability rating did not differ between the SPRC and CHO gel during exercise at 80% VO_2max and immediately after the time trial. In conclusion, pre- and during exercise ingestion of the SPRC suppressed sweetness, thirst, and hungry ratings without interfering with exercise performance.

Recent progress in sweetpotato breeding and cultivars for diverse applications in Japan

Sweetpotato (Ipomoea batatas (L.) Lam.) is an outcrossing hexaploid that is cultivated in the tropics and warm-temperate regions of the world. Sweetpotato has played an important role as a famine-relief crop during its long history and has recently been reevaluated as a health-promoting food. In Japan, sweetpotato is used for a wide range of applications, such as table use, processed foods, and alcohol and starch production, and two groups at National Agriculture Research Organization (NARO) undertake the breeding of cultivars for these applications. Sweetpotato breeders utilize breeding processes such as grafting for flower induction and the identification of incompatibility groups before crossing to conquer problems peculiar to sweetpotato. For table use, new cultivars with high sugar content were released recently and have become popular among Japanese consumers. New cultivars with high anthocyanin or β-carotene content were released for processed foods and use as colorants. As raw materials, new cultivars with high alcohol yield were released for the production of shochu spirits. In addition, new cultivars with high starch yield and a cultivar containing starch with excellent cold-storage ability were released for starch production. This review deals with recent progress in sweetpotato breeding and cultivars for diverse applications in Japan.

Carbohydrate components in sweetpotato storage roots: their diversities and genetic improvement

Carbohydrates are important components in sweetpotatoes in terms of both their industrial use and eating quality. Although there has been a narrow range of diversity in the properties of sweetpotato starch, unique varieties and experimental lines with different starch traits have been produced recently both by conventional breeding and genetic engineering. The diversity in maltose content, free sugar composition and textural properties in sweetpotato cultivars is also important for their eating quality and processing of storage roots. In this review, we summarize the current status of research on and breeding for these important traits and discuss the future prospects for research in this area.