This study was conducted to clarify the characteristics of phosphorus absorption in buckwheat (Fagopyrum esculentum Moench) and to elucidate the reasons for low seed yield in Kunigami-maaji soil cultivation. Buckwheat growth and seed yield were drastically suppressed in the treatment with no phosphorus fertilizer. At harvest time, root dry weight in the low-phosphorus condition was larger than that in the high-phosphorus condition, as root growth was promoted or prolonged after the flowering stage, which seemed to lead to greater nutrient absorption in the low-phosphorus treatment. In addition, both the concentrations and uptakes of phosphorus in the leaves and stem decreased after the flowering stage, while the phosphorus concentration in seeds remained around 2.5 g/kg in the low-phosphorus condition. Thus, it appears that the phosphorus in leaves and stem is remobilized to the seeds after the flowering stage to keep the seed phosphorus concentration at that level. These two phosphorus-absorption characteristics of buckwheat seem to underlie the crop’s tolerance of low phosphorus. Furthermore, our experiments also revealed that the decrease of growth and yield was severe when buckwheat was cultivated with Fe-bound phosphorus, whereas the decline was small with Al-bound phosphorus.

We flooded the paddy rice for 1 or 3 days at the late spikelet differentiation stage or the pollen formation stage or 2 days at the early ripening stage or the middle ripening stage, and examined the effects on rice yield components. None of the flooding treatments affected the panicle number. The panicle weight per ear was reduced by 13 to 17% by flooding treatment for 3 days in the late spikelet differentiation stage, and by that for 1or 3 days in the pollen formation stage and in the early ripening stage compared with that of the control. The decrease in one panicle weight due to flooding treatment was mainly due to the decrease in the number of secondary rachis grains caused by the decrease in secondary rachis branches. There was no difference in the one grain weight of the treatment plots in comparison with that of the control. The decrease in yield is mainly due to the decrease in the number of grains due to the abortion or death of the secondary rachis branch.

NARO recently developed rice (Oryza sativa L.) cultivars, “Akidawara”, “Yamadawara” and “Toyomeki” which had high yield and high eating quality. The filled brown rice yield of these cultivars was approximately 800 g m^–2, while that of a popular cultivar “Koshihikari” was 500 g m^–2. The higher yield was attributed to the larger number of total spikelets m^–2. To determine the suitable harvesting time of these cultivars to optimize grain yield and quality, we examined the correlation of accumulated temperature after heading with the perfect grain ratio, water content of hulled grain, percentages of filled spikelets and hulled grain yellowing rate. The accumulated temperature after heading, where the percentage of perfect grain was more than or equal to 70% and water content of hulled grain was less than or equal to 25%, was 1115–1393, 1247–1441 and 1171–1480ºC・day, in “Akidawara”, “Yamadawara” and “Toyomeki”, respectively. This was when the percentage of filled spikelets reached almost the maximum level and the hulled grain yellowing rate was 88–95, 87–94 and 82–92%, in “Akidawara”, “Yamadawara” and “Toyomeki”, respectively. Therefore, these ranges of accumulated temperatures were concluded to be the suitable harvesting time.

Demand for sweetpotatoes with high sugar content has increased owing to a recent increase in consumer preference for sweetness. The influence of cultivation method and storage on quality characteristics was investigated using normal and high sugar content varieties of sweetpotatoes. We investigated the effects of plastic film mulching and cultivation period in 2014, and cultivation period with film mulching and postharvest two-week storage in 2017. In 2014, the cultivation method affected the pasting temperature of starch and the content of dry matter, starch, and Brix sugar in sweetpotatoes. In 2017, the cultivation period affected the root yield, pasting temperature, β-amylase activity, and content of dry matter, starch, Brix sugar, sucrose, and soluble protein in sweetpotatoes. Furthermore, short-term storage increased the content of Brix sugar, reducing sugars, and sucrose, but decreased the content of maltose. In comparison with normal varieties, recently developed varieties with high sugar content were characterized by higher maltose content derived from low pasting temperature and higher β-amylase activity, and higher sucrose content that was increased by short-term storage. However, a decrease in the pasting temperature did not result in an increase in the Brix sugar content in the late cultivation plot. Thus, the use of high sugar content varieties, application of plastic film mulching and suitable cultivation period to increase the starch content and β-amylase activity, and postharvest storage to increase sugar content were considered effective to obtain stable production of sweetpotatoes with a high sugar content.

We investigated culm strength associated with lodging resistance of 18 main wheat cultivars raised in each region of Japan. “Yumechikara” had the smallest lodging index and was considered to have the highest lodging resistance among 18 cultivars. “Yumechikara” which had the largest bending moment at the breaking point of the basal internode with leaf sheath exhibited large bending stress and section module. “Yukichikara”, “Kinunonami”, “Ayahikari” and “Chikugoizumi” also had a large bending moment at the breaking point. Among them, “Yukichikara” and “Chikugoizumi” had a large bending stress and medium section module, while “Kinunonami” and “Ayahikari” had medium bending stress and large section module. In this study, cultivars that were bred in Hokkaido region had larger cross sectional area and spikelet number per spike than cultivars that were bred in Kyushu region, while cultivars bred in Kanto region had intermediate values. It was suggested that “Yumechikara” had high resistance to both stem bending and breaking lodging, and the trait related with culm strength was different in each breeding area. Furthermore, among cultivars with a large bending moment at the breaking point, there were cultivars with large bending stress and medium section module, and cultivars with medium bending stress and large section module. It was considered possible to raise a greater cultivar with lodging resistance by crossing between cultivars with such different traits.

In 2017, intensely yellow-colored grains(YCG)occurred in seed production fields of two-rowed barley cultivar “Haruka-Nijo” in Fukuoka prefecture. Color characteristics of the kernels were different from those of discolored kernels, an important type of grain damage in hulled barley. The factors affecting the occurrence of YCG, and the effects of YCG on seed quality were unknown. To investigate the factors affecting the occurrence of YCG, the correlation between three grain color values(L* value: brightness, a* value: redness and b* value: yellowness)and weather conditions were investigated. As a result, the L* value decreased while both a* and b* values increased in grains subject to 2.5 mm rainfall from the maturation period to harvest. A similar trend for color change of grains was confirmed when detached ears, not subject to rainfall subsequent to ear emergence, were treated at high humidity for 2 days. Furthermore, there are indications that a* and b* values are likely to increase in “Haruka-Nijo” as compared to other popular cultivars in Fukuoka. Results of analyzing the relationship between grain color values and seed quality, i.e., germination rate, thousand grain weight, and seed dormancy, showed that YCG is not inferior to normal color grains. These results show that YCG in “Haruka-Nijo” occurs due to very limited rainfall from the maturation period to harvest, and does not affect seed quality.

Utilizing the data obtained during the past 20 years, we analyzed the effects of meteorological factors, including typhoons, which were not considered previously, on sucrose accumulation in sugarcane during the maturation period (October to January) using a standard variety “NiF8” in Tanegashima-island. The juice sucrose content was measured periodically and sucrose accumulation was calculated. Multiple regression analyses between meteorological factors and sucrose accumulation were conducted. In the analyses, the effect of a typhoon was defined as the inhibition of photosynthesis caused by leaf lesion and the hypotheses were 1) the inhibitory influence should last from the date of typhoon to 200 °C days in effective accumulated temperature, and 2) the efficiency of utilization of solar radiation should be reduced by the inhibition depending on the wind speed levels. Determination coefficient of the model was highest when the inhibition of photosynthesis was assumed to be 10% at maximum instantaneous wind speed of 20–30 m s^–1 and 60% at that over 30 m s^–1. By including the typhoon effects in the model, the estimated sucrose accumulation was closer to the observation data in 2017/2018 growing season when sugarcane was affected by two typhoons in late October; and, the estimation accuracy was higher compared to the model that did not include the typhoons. Results of the analyses indicated that solar radiation usable by sugarcane from October to December, and temperature and precipitation from November to December had significant effects on sucrose accumulation.

To select standard rice cultivars for evaluating tolerance to kernel cracking, we investigated cracking tolerance at 2 breeding stations of Japan in 2015 to 2018. Based on the percentage of cracking rice determined by using the late harvesting method, we selected 8 new standard cultivars from ‘tolerant’ to ‘weak’ in medium and medium-to-late heading groups in the western region and regarded “Yamadawara” as a ‘tolerant’ standard cultivar. All 8 new standard cultivars could also be evaluated by the soaking method using unhulled brown rice and the moisture absorption method using brown rice harvested at the proper time. These methods were considered to be useful as alternatives to the late harvesting method.

Excessive vegetative growth, leading to decreased yield of sweet potato (Ipomoea batatas (L.) Lam.), is common in wet lowland soils. In this study, we found that both the yield and the quality of storage roots of the cultivar “Kenroku” grown in an unflooded paddy field were comparable to those of plants grown in an upland sandy loam field. Compared with fertilization at the time of transplanting, delayed fertilization at 8 weeks after transplanting in an unflooded paddy field significantly increased the average weight and total yield of the storage roots, although it decreased the number of storage roots. The surface corrugations that are frequently observed on storage roots grown without fertilization and that decrease the productivity of processing were rare in cultivation with delayed fertilization. Different fertilizer application methods did not affect the sugar and β-carotene contents of the storage roots. These results strongly suggest that “Kenroku” is a feasible candidate variety in paddy–upland rotations without the needs of drainage measures such as permanent conversion of fields or farmland consolidations.

The effect of storage temperature on the quality of the sweet potato (Ipomoea batatas (L.) Lam.) cultivar “Kenroku” was investigated. In general, sweet potato storage roots are stored at 13°C to avoid chilling injury. Although flesh decay was not observed at this temperature, the sucrose content and sweetness index of “Kenroku” storage roots did not change during 12 weeks of storage at 13°C. Storage at 16°C induced sprouting within 4 weeks, suggesting that this temperature is inappropriate for longer storage durations. In contrast, cold storage at 6 or 9°C increased the sucrose content and sweetness index for the first 6 and 10 weeks, respectively, after the start of storage; subsequently, the flesh started decaying. With unheated storage, the sucrose content and sweetness index began increasing 4 weeks after the start of storage, when the daily average temperature fell below 10°C, and continued to increase 12 weeks after the start of storage, when the flesh began decaying. Because “Kenroku” has been cultivated to produce steamed and dried slices and is harvested at the end of October, our results suggest that cold storage at temperatures of 6 to 9°C is suitable if the storage roots will be processed by the end of the year, whereas unheated storage is available if processing will occur early in the next year.

The farmers who must meet the demands of the food service industry for less expensive rice, while securing their income, need a technique for high and stable yield. To clarify the suitable yield level of a cultivar “Akebono” for the farmers, I examined grain yields, yield components, lodging indices and inspection grades of grain quality, under several different amounts of fertilizer application in Okayama prefecture, Japan, for three years. Both in 2016 and in 2017, grain yield reached 700 g per m² without heavy lodging in one experimental plot, but not in 2018 when sunshine was lacking during the maturing stage. In order to reach this yield level, approximately 33000 spikelets per m² was required, and the percentage of ripened grains had to be kept above 86%. On the other hand, increase in the number of spikelets per m² above 33000 led to a higher risk of heavy lodging and poor grain quality. Therefore, I concluded that the suitable level of grain yield was 700 g per m² for “Akebono”. A new technique needs to be developed to produce constantly 33000 spikelets per m² and keep the percentage of ripened grains above 86%.

Rapid generation advancement for rice breeding is actively undertaken at the Tropical Agriculture Research Front, Japan International Research Center for Agricultural Sciences in Ishigaki Island, in the southernmost part of Japan. Rice populations are grown there twice or thrice a year in order to shorten the breeding time. Twenty-nine Japanese rice varieties originating from the northern region of Hokkaido to the southern region of Kyushu were cultivated in the paddy fields. Although all varieties showed normal fertility at first cropping (sown on 4th March), most of the varieties from the west of the Kanto region showed more than 10% sterility during second cropping (sown on 15th July) and late cropping (sown on 28th August). In particular, some varieties from the Kyushu region, viz.,“Shinrei,”“Nishihomare,”and “Saiwaimochi,” showed nearly 60% sterility during late cropping. The temperature during these cropping seasons was neither too high nor too low to induce sterility. With delayed cropping, days to heading became shorter, particularly in strongly photo-sensitive varieties from the west of the Kanto region. Sterility was thought to be related to the shortening of heading time under short-day conditions.