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One complementary or alternative control measure to chemical insecticide is interplanting of plants that affect insect behavior. While few successes are known based on interplanting of different varieties of the same crop, such intra-crop interplanting may be effective against insects that feed on a limited range of plants and have persistent preference to one cultivar. Here, we report three field trials that examined the efficacy of intra-crop interplanting of sweet potato varieties, Ipomoea batatas (L.) Lamarck (Solanales: Convolvulaceae), on an oligophagous weevil, Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae), planting a preferred variety, Beni-masari, together with a less preferred one, Kyushu 166. In the first experiment, Beni-masari was planted as a border around Kyushu 166 and this arrangement decreased tuber damage in the main crop (Kyushu 166), although damage reduction was not statistically significant from monoculture plantings of Kyushu 166. In the second experiment, both varieties were planted in plots spaced 3 m apart to test the attractiveness of Beni-masari to weevils from Kyushu 166. No attractive effects of Beni-masari were observed. In the third experiment, the two varieties were planted in separate plots that were contiguous to each other, and in this experiment Beni-masari preferentially attracted weevils away from Kyushu 166 within 3 m distance, and tuber damage in Kyushu 166 within that zone was reduced owing to the attractiveness of Beni-masari. We discuss the potential of the intra-crop interplanting in pest management.

Wheat (Triticum aestivum L.) grain yield is predicted to decrease in the future because of an increase in air temperature globally. To clarify the effects of the vernalization response gene in wheat to warmer winters, we compared dry matter production and grain yield between spring wheat ‘Asakazekomugi’ and its winter-type near-isogenic line (NIL) carrying different alleles of the vernalization response gene Vrn-D1 under early-, standard-, and late-sowing conditions. Under early-sowing conditions, dry matter production of the NIL carrying the winter allele of Vrn-D1, named Asa (Vrn-D1b), exceeded that of ‘Asakazekomugi’ from mid-March (after stem elongation in Asa (Vrn-D1b)) when the temperatures rose. Tiller number and leaf area index under early-sowing conditions were consistently higher in Asa (Vrn-D1b) than in ‘Asakazekomugi’ from mid-March onward. It was suggested that the early-sown ‘Asakazekomugi’ could not effectively absorb solar radiation to produce dry matter because of the acceleration of stem elongation caused by the Vrn-D1 gene during the cold season. The grain yield of Asa (Vrn-D1b) with early sowing was higher than with standard sowing. In contrast, the grain yield of ‘Asakazekomugi’ was lower in the early-sown crop than in the crop sown at the standard date. These results suggested that the higher grain yield of Asa (Vrn-D1b) than that of ‘Asakazekomugi’ under early-sown conditions could be due to Asa (Vrn-D1b) maintaining high dry matter production after the jointing stage by suppressing acceleration of growth caused by warm conditions after sowing. Abbreviations CGR: crop growth rate; HI: harvest index; LAI: leaf area index; NIL: near-isogenic line; SNP: single-nucleotide polymorphism

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.

To change the major anthocyanin in the storage roots of sweetpotato (Ipomoea batatas) from purplish cyanidin derivatives to reddish pelargonidin derivatives, the dosage of a recessive allele in the F3’H gene locus was enriched by successive crossing and allele dosage estimation. A putative recessive allele of the F3’H gene, named f3’htm, was found in the cultivar Tanegeshimamurasaki and contained a 57-bp deletion causing a premature stop codon. Starting with the parents having a simplex f3’htm allele, plants considered to be homozygous with f3’htm were obtained in the F4 generation. The storage roots and other pigmented tissues of the homozygous plants showed a reddish color, whereas the original parents or F4 plants without homozygous f3’htm were purplish. More than approximately 90% of the anthocyanins in the storage roots of plants with homozygous f3’htm were pelargonidin derivatives. These results suggest that allele dosage–dependent selection is also possible in autohexaploid crops to develop mutants with novel phenotypes. In addition, the obtained plants with homozygous f3’htm can be important materials for breeding sweetpotato cultivars for pelargonidin production.

Sweetpotato (Ipomoea batatas (L.) Lam.), which is an outcrossing hexaploid, is one of the most important starch-producing crops in the world. During the last decade, new sweetpotato cultivars, e.g. ‘Quick Sweet’, which have approximately 20°C lower pasting temperature, slower retrogradation and higher digestibility of raw starch than ordinary cultivars, have been developed in Japan. Genetic analysis of these variants with low pasting temperature starch was conducted in this study. Using 8 variants and 15 normal clones, 26 families were generated. The results from analyzing these progenies suggested that this trait is a qualitative character controlled by one recessive allele (designated spt), which is inherited in a hexasomic manner. A dosage effect of the wild-type Spt allele was found for starch pasting temperature, although the effect was not linear. These results will aid breeders to develop sweetpotato cultivars with a range of starch pasting temperatures.

The sweet potato is recognized as a health-promoting food, owing to its richness in functional components such as dietary fiber; however, only a few studies have been conducted on resistant starch (RS) levels in the sweet potato. Now, the sweet potato is expected to have potential as a renewable resource for bio-ethanol production. The enzymatic digestibility of raw starch appears to influence the conversion rate of starch to sugar in the first step of ethanol production. In this study, the RS content of gelatinized starch, digestible starch (DS) content of raw starch and other starch properties were investigated using 21 sweet potato cultivars and lines to assess varietal variations and to estimate relationships among these starch properties. The RS content of gelatinized starch ranged between 1.8 and 9.5%. The DS content of raw starch ranged between 69.3 and 98.3%. Analysis of variance indicated that the varietal differences were significant at the 0.1% level for both the RS content and the DS content. Sweet potato starches with high amylose content and low paste viscosity showed high RS content of gelatinized starch. Starches with low pasting temperature and slow retrogradation showed high DS content of raw starch. A new breeding line, Kyukei 03284-156, contained a unique starch having the highest RS content, highest amylose content, lowest paste viscosity and abnormal granule morphology. The results of this study are expected to provide useful information to food industries that utilize sweet potato starch and to breeders that attempt to improve the RS and DS contents in sweet potato cultivars.

11品種の有色サツマイモ（白色 : 3，黄色 : 2，橙色 : 2，紫色 : 3）の凍結乾燥品から高速溶媒抽出装置を用いて抽出液を調製し，DPPHラジカル消去能とORACを測定した．サツマイモのDPPHラジカル消去活性は肉色が白，黄，橙では同程度であったが，紫サツマイモは他の肉色のサツマイモと比べて約10倍高い活性を示した．ORAC値もDPPHラジカル消去活性と同様な傾向であり，ETとHATを反応原理とする2つの評価系で紫サツマイモが高い抗酸化活性を示した．20品種・系統の紫サツマイモにおいて，主要アントシアニンの含量とORAC値との間に正の相関（R＝0.833）が認められ，アントシアニンがORAC法での主要な抗酸化成分であると判断された．また，紫サツマイモのDPPHラジカル消去活性がORAC値と高い相関（R＝0.894）を示したことから，DPPHラジカルを用いた評価法がORAC値を見積もるための方法として利用できると考えられた．

This is the first report on successful production of somatic hybrid between cross-incompatible cultivars of sweet potato, lpomoea batatas (L.) Lam. The protoplasts of sweet potato cultivars, Koganesengan and Bitambi, belonging to the same cross-incompatible B group and not crossing with each other, were fused with Polyethylene Glycol (PEG) solution and then cultured in modified liquid MS (Murashige and Skoog 1962) medium containing 0.05 mg/l 2, 4-dichlorophenoxyacetic acid (2, 4-D) and 0.5 mg/l kinetin. Forty-five plants were obtained from the calli on the hormone-free medium by using the callus proliferation medium either supplemented with 2, 4-D and kinetin or abscisic acid (ABA), or supplemented with naphthalene aceic acid (NAA) and 6-benzylaminopurine (BAP). Two plants were considered to be the somatic hybrids by analyzing their morphology, chromosome numbers and random amplified polymorphic DNA (RAPD) markers. The hybrids showed intermediate characters in leaf shape and leaf color between the two parents and had chromosome numbers that correspond to the sum of their parents (2n= 12x (2n+2n)= 180). By RAPD assay, they expressed some of the bands from both parents. They grew slowly in the field. One of them had the pollen fertility of 12.2 % when grafted on the morning-glory for flower induction. No seed was obtained by crossing with pollen of Kyushu No. 30 (cross-incompatible C group cultivar).