To reveal the genetic regions controlling eating quality of japonica rice and to establish a system for markerassisted selection (MAS), we conducted a QTL analysis for eating quality of Koshihikari, a leading cultivar in Japan. We used a recombinant inbred population consisting of 92 lines derived from a cross between two closely related japonica cultivars, Moritawase (low eating quality) and Koshihikari. We evaluated overall eating quality (OE), glossiness (GL), taste (TA), stickiness (ST), and hardness (HD) of the lines over 3 years by sensory tests. QTL analysis revealed 43 QTLs on 16 regions across all chromosomes except chromosome 5. QTLs on chromosomes 1, 3, 6, 7, and 10 were detected in multiple years. The Koshihikari alleles at 37 QTLs increased the eating quality. Further QTL analysis revealed 8 QTLs for textural characteristics of cooked rice and 3 for the amino acid ratio of polished rice. Those on chromosomes 1, 3, 6, and 7 were located near the QTLs for eating quality.

In order to establish a system for marker assisted selection (MAS) to develop new rice cultivars with good eating quality, we conducted QTL analyses for physicochemical properties of rice by using a recombinant inbred (RI) population consisting of 92 lines derived from a cross between closely related japonica cultivars, Moritawase (a cutivar with low eating quality) and Koshihikari (a cultivar with good eating quality). We developed a linkage map with 119 simple sequence repeat (SSR) markers. Physicochemical properties of rice were evaluated two years by measuring protein content, amylose content and textural characteristics. QTL analysis for protein content revealed three QTLs on chromosome 2, 6 and 9. Four QTLs for amylose content were detected on chromosome 3, 7, 9 and 12. One QTL for texture characteristics were identified on chromosome 3. The DNA markers linked to these QTLs will be used for the MAS for good eating quality.

There is increasing evidence that global warming affects the development of rice. High temperatures during ripening increase the ratio of undesirable chalky grains followed by deteriorating grain appearance quality. In order to detect quantitative trait loci (QTLs) controlling the occurrence of white-back and basal-white chalky grains of brown rice, QTL analysis was performed using recombinant inbred lines derived from a cross between two strains, ‘Tsukushiroman’ (sensitive to heat stress) and ‘Chikushi 52’ (tolerant of heat stress). The F7 and F8 lines were exposed to heat stress during the ripening period in two locations, Fukuoka and Kagoshima, in Japan. QTLs for white-back grains and basal-white grains were detected on chromosomes 1, 3, and 8, and those for basal-white grains were detected on chromosomes 2, 3, and 12. QTLs on chromosome 8 for white-back grains were shared in the plants grown in both locations. Near-isogenic lines (NILs), which harbored a segment from ‘Chikushi 52’ on chromosome 8 with the genetic background of ‘Tsukushiroman’, showed relatively lower ratios of white-back grains than ‘Tsukushiroman’. Therefore, insertion of the ‘Chikushi 52’ genomic region of the QTL on chromosome 8 can improve the quality of rice when it is grown under heat stress conditions.

Adenosine 5′‐diphosphate pyrophosphorylase (AGPase) is a key enzyme governing starch synthesis and is regarded as an important determinant of the sink activity of the sweet potato root. In this study, assuming that the expression of AGPase is under the direct or indirect control of sucrose, we investigated the effect of exogenous injection of sucrose solution into a plant on the activity of AGPase and tuberous root production. Sucrose solutions of 6 and 12 %, and distilled water as the control, were injected into the top of the shoot. The application of sucrose solution was effective in increasing tuberous root production and increasing the ratio of tuberous root weight to total root weight in a plant. AGPase activity in roots was enhanced by about 25 % by injecting sucrose solution. These results suggest that AGPase and sink activities are controlled by sucrose transported from the leaves. To increase sweet potato production effectively, AGPase activity and sink function must be enhanced, and so a genetic and physiological improvement in photosynthetic function or sucrose productivity in the leaves is necessary to increase AGPase activity in sink organs.

A strawberry Multi-parent Advanced Generation Intercrosses (MAGIC) population, derived from crosses using six strawberry cultivars was successfully developed. The population was composed of 338 individuals; genome conformation was evaluated by expressed sequence tag-derived simple short repeat (EST-SSR) markers. Cluster analysis and principal component analysis (PCA) based on EST-SSR marker polymorphisms revealed that the MAGIC population was a mosaic of the six founder cultivars and covered the genomic regions of the six founders evenly. Fruit quality related traits, including days to flowering (DTF), fruit weight (FW), fruit firmness (FF), fruit color (FC), soluble solid content (SC), and titratable acidity (TA), of the MAGIC population were evaluated over two years. All traits showed normal transgressive segregation beyond the founder cultivars and most traits, except for DTF, distributed normally. FC exhibited the highest correlation coefficient overall and was distributed normally regardless of differences in DTF, FW, FF, SC, and TA. These facts were supported by PCA using fruit quality related values as explanatory variables, suggesting that major genetic factors, which are not influenced by fluctuations in other fruit traits, could control the distribution of FC. This MAGIC population is a promising resource for genome-wide association studies and genomic selection for efficient strawberry breeding.