Male sterility induced by low temperature at the reproductive stage is a critical factor for rice production in cool climates. This review summarizes the threshold temperature for inducing male sterility, a methodology for quantification of cold damage, and physiological and molecular mechanism inducing sterility especially focusing on genotypic variations. Recent advance of the analysis of Quantitative Trait Locus (QTL) revealed several candidate regions on the chromosome, and pyramiding genes coding cold tolerance into a cultivar has been successfully conducted, resulting in improvement of cold tolerance. The future perspective of research of cold damage will be discussed.

In this study, two experiments (Experiment 1&2) were conducted to investigate the effects of chisel plowing on soil conditions and nitrogen absorption of maize (Zea mays L.) in upland fields converted from an andosol paddy field. In Experiment 1, two hybrids were planted under two tillage systems (rotary tilling and chisel plowing), and soil physics, soil chemistry and nitrogen absorption of maize were examined. In Experiment 2, the difference in fertilizer distribution between the two tillage systems was examined. In Experiment 1, the soil penetration resistance value at 0–5 cm depth was nearly the same in the two tilling systems, whereas, at 5–20 cm depth it was larger in the chisel plowing system, than in the rotary tilling system. In the chisel plowing system, the percentage of gas phase at 10 and 20 cm depth was lower and that of the solid phase was higher than in the rotary tilling system. Contents of nitrate nitrogen, exchangeable potassium and available phosphorus at the 6-leaf stage were higher in chisel plowing than in rotary tilling at a 0 –10 cm depth, whereas there were no significant differences between the two tillage systems at the maturity stage. There was no significant difference between the two tillage systems. In Experiment 2, more than 95% of fertilizer was distributed at 0–10 cm in the chisel plowing system, whereas in the rotary tilling system, the fertilizer distribution was almost uniform at 0–20 cm depth. It is concluded that, in the chisel plowing system, penetration resistance was high at 5–20 cm, and furthermore, fertilizer and soil nutrient were concentrated at 0–5 cm at the early growing stage. It is also concluded that chisel plowing allows farmers high-speed work while maintaining nitrogen absorption at the same level as in rotary tilling in an upland field converted from a paddy field.

In order to elucidate the optimum harvesting time of the black seeded soybean “Tanbaguro” for new edamame (green soybean) “Murasakizukin 2”, we examined the changes in the thickness and appearance of pods during the seed growth in 2007–2009. A significant linear relationship was found between pod thickness and the days or accumulated mean air temperature after flowering. The analysis of covariance revealed that the slope of the regression line did not significantly vary with the year. The percentage of pods with more than 11 mm in thickness reached 70% when the accumulated temperature after flowering exceeded 1250ºC in the mid-June-sowing cultivation (conventional sowing) in all three years. The commercial value of green soybean is lost by appearance of yellow pods, and it occurred when the accumulated temperature after flowering exceeded 1380ºC. These results suggested that the optimum harvesting time of “Murasakizukin 2” could be estimated by the accumulated temperature after flowering. In addition, the tendency of increasing pod thickness at the uppermost four nodes of the main stem was similar to that in the whole plant. Therefore, the pod swelling in the whole plant could be grouped by that at the uppermost four nodes.

To improve seedling establishment of non-coated rice seeds direct-seeded with a puddling seeder, the effects of germination level at the time of seeding on seedling establishment and early growth were investigated. Seeds with coleoptiles shorter than 1 mm (pre-germinated seeds), coleoptile-elongated seeds, root-elongated seeds, coleoptile-removed seeds, and root-removed seeds (all non-coated seeds) were seeded in a growth cabinet, and seedling emergence, establishment, and growth were assessed. Seeds with elongated coleoptiles and roots exhibited faster seedling emergence and better seedling establishment and better growth than the pre-germinated seeds. The root-removed seeds also showed similar seedling establishment, but the coleoptile-removed seeds showed poor seedling establishment. This suggests that root-elongated seeds are more useful than the coleoptile-elongated seeds, for direct seeding using a seeding machine. To elucidate the effect of the root-elongated seeds used for direct seeding on seedling establishment and early growth, field experiments were conducted in 2015 and 2016. The root-elongated seeds and pre-germinated seeds were seeded in early April and usual mid-May. The root-elongated seeds showed improved seedling establishment and early growth in both experiments with different seeding time, optimum- and low-temperature conditions. Therefore, using root-elongated non-coated seeds is considered to improve seedling establishment in direct seeding with a puddling seeder.

We examined the agricultural characteristics and sake brewing aptitude of two Hokkaido brewers'rice varieties “Ginpuu” and “Suisei” cultivated in two regions of Hokkaido, Iwamizawa and Pippu. The brown rice yield was higher in “Ginpuu” and “Suisei” than in the table rice varieties “Yumepirika” and “Nanatuboshi” due to heavier 1000 grain weight, and was higher in “Suisei” than in “Ginpuu” due to lower sterility rate and heavier 1000 grain weight. The crude protein content of Pippu rice was lower than that of Iwamizawa rice, and that of “Suisei” was lower than that of “Ginpuu”. The selection of cultivation region and variety is important to reduce the protein content in brewers'rice. The 20-minute water absorption rate (20WR) was lower in “Suisei” than in “Ginpuu” due to lower occurrence rate of white core rice. The steamed water absorption rate of rice did not significantly vary with the region or variety. The lodging resistance and brown rice yield of the two Hokkaido brewers'rice varieties in the two regions were superior to those of “Yamadanishiki” cultivated in Hyogo prefecture, but the 1000 grain weight, crude protein content, 20WR and steamed-water absorption rate of the two Hokkaido brewers'rice varieties in the two regions were inferior to those of “Yamadanishiki”. It is necessary to improve the sake brewing aptitude rice to the same level as that of “Yamadanishiki” cultivated in Hyogo prefecture by breeding and by improving the cultivation method.

Rice stink bugs are one of the most important rice pests, which cause pecky rice. Effective bioassay methods have been developed to assess the resistance of newly bred rice to these pests. The most suitable time for release and the release period of rice stink bugs were examined. Adults of the rice bug Leptocorisa chinensis were released on four rice cultivars. By releasing the rice bug at 15 and 20 d after heading, differences in the resistance between cultivars became quantitatively evident. At 20 d after heading, we released the rice bugs on each cultivar for various periods. As the release period was lengthened, the rate of the incidence of pecky rice increased and differences in the resistance among the cultivars became evident 4 d after the release. On the other hand, a simple bioassay using cut panicles was performed. The panicles cut at the third internode below the node of the second leaf from the flag leaf at 20 d after heading were grown with the cut end in water. Exposed to L. chinensis for 7 d, and pecky rice incidence was investigated. Differences in the resistance to the rice sting bugs between the two methods were evident. Thus, the simple cut panicle bioassay method was effective for the selection of resistant cultivars and reduced the labor for breeding.

Improvement of cane yield is essential to enhance sugar productivity in the South-western islands of Japan. In the present study, to identify certain traits related to high yield in the South-western islands, we investigated the growth and dry matter production of three high yielding backcrossed first generation (BC1) clones developed by back-crossing an interspecific hybrid derived from Saccharum spontaneum with commercial cultivars. Shoot and root dry weights, and other related traits including leaf area index and specific leaf area of the BC1 clones were measured at different growth stages, and were compared with those of commercial cultivar. The BC1 clones showed 30–58% higher yield, higher specific leaf area at the initial growth stage, higher leaf area index and leaf dry weight throughout the growth period, and vigorous root development at the initial growth stage. Although the photosynthetic rate was also measured during the growth period, there was no significant difference between the commercial cultivar and the BC1 clones. In conclusion, higher yield of the BC1 clones was suggested to be achieved by higher partitioning of assimilates to the leaf at the initial growth stage followed by rapid increase in leaf area index. Better root system development especially at the initial growth stage could contribute to supply enough water and nutrients to the shoot.

The Kumamoto Earthquake in 2016 caused severe roughness of paddy fields in Kumamoto-city, However, leveling of the soil surface was not performed before planting soybean seeds. Thus, it was anticipated that soybean plants grown in concave positions were exposed to wet injury. In this study, we examined the effect of the roughness of the soil surface on the growth and yield of soybean. The seed yield in the concave position was decreased 50% by the reduction in the number of pods m–2 compared with seed yield in the convex position. The reason for the reduction in yield was that soybean root in the concave position was damaged by wet injury, which depressed nodule activity and water uptake ability. Therefore, leveling of the soil surface should be performed for succeeding sustainable crop production in such fields. If leveling is not practical, planting seeds which were disinfected and regulated in moisture content should be used for reducing the damage by wet injury in the concave position. Furthermore, it might be effective for enhancing the drainage from the field to dig an open ditch in the concave position.

Seed coat cracking appearing in a soybean cultivar “Satonohohoemi” was investigated for 3 years in relation to planting time and environmental conditions during the seed-filling period. Two types of cracked seeds, one with irregular cracks that accounted for a major part of the cracked seeds and the other with line-shaped cracks, were observed. Late planting in mid-June significantly reduced the occurrence of both types of cracking but its effect on irregular cracks was much larger than that on line-shaped cracks. No significant correlation was detected between the occurrence of irregular cracks and 100-seed weight during the 3-year experiment, which suggests that factor(s) other than seed size may be involved as a major factor in reducing irregular cracks by late planting. Since the flowering date rather than planting date was highly correlated with the occurrence of irregular cracks, the effect of late planting on the occurrence of irregular cracks may arise through delaying flowering time. Therefore, flowering time can be a practical indicator to predict the occurrence of irregular cracks in the cultivar. In addition, the number of days and accumulated temperature during the seed-filling period also showed a relatively high correlation with the occurrence of irregular cracks. Line-shaped cracks exhibited a significant, positive correlation with solar radiation during seed-filling and a higher correlation with planting date than with flowering date. Irregular and line-shaped cracks may be caused by different physiological mechanisms.


Hot water treatment of rice seed is a common disinfection method that requires no agricultural chemicals. However, the effect of hot water treatment on seed germination remains unclear. In the present study, we examined the effect of the treatment with 60°C water for 10 minutes on seed germination and seedling emergence in Hokkaido rice cultivars under normal and low temperature conditions. Under the normal temperature (27ºC) conditions, hot water treatment only slightly improved the early germination rate. In contrast, under low temperature (15ºC) conditions, germination was promoted by the hot water treatment. Germination of rice seeds harvested in 2014 was more promoted by hot water treatment than those harvested in 2015. In “Nanatsuboshi”, “Yumepirika” and “Oborozuki” cultivars harvested in 2014, seedling emergence rates under low temperature conditions were improved by hot water treatment. Thus, hot water seed treatment is a possible sterilization method for direct-seeding, which promotes seed germination and seedling emergence in Hokkaido rice cultivars grown under low temperature conditions.

In a specific area in the northern mountainous region of Sasebo city, Nagasaki, a strange disorder called ‘Rice Hagare Symptom’ has been observed for over 40 years. In the paddy fields where the Rice Hagare Symptom was observed, we examined the effects of water management on the occurrence of the Rice Hagare Symptom and yield for 3 years. Under the ordinary water management, the redox electric potential of the paddy soil was low showing a strong reduced state and the upper leaves on the rice plant started to wither from 40 days after transplanting. Such a rice community showed many yellowish brown spots in the field, and had reduced yield. We drained and dried the paddy fields 2 or 3 times each for 3–7 days after the midseason drainage period. By this treatment the redox electric potential was elevated, and the Rice Hagare Symptom diminished. The ripening rate and yield were also increased especially in the hot year when yield is reduced. The effect of the drainage was low in the cold year. It was reported that the growth disorder due to soil reduction was caused by excess or lack of nourishment. From the inorganic component content of rice plant and physicochemical property of soil we considered that the Rice Hagare Symptom is probably caused by excess iron.

Fourteen standard rice varieties with high temperature tolerance at the ripening stage in Kyushu region were selected based on apparent by an evaluation of grain quality after ripening under high temperature condition at eight breeding stations, NARO Kyushu Okinawa Agricultural Research Center, Fukuoka Agriculture and Forestry Research Center, Saga Agricultural Research Center, Nagasaki Agricultural and Forestry Technical Development Center, Kumamoto prefectural Agricultural Research Center, Oita Prefectural Agriculture, Forestry and Fisheries Research Center Agricultural Research Division, Miyazaki Agricultural Research institute and Kagoshima Prefectural Institute for Agricultural Development. In the very early and early heading variety groups, four varieties “Natsuhonoka”, “Mineharuka”, “Nipponbare” and “Koganebare” were selected as having strong, moderately strong, middle and moderately weak tolerance to high temperature, respectively. Two varieties, “Hatsuboshi” and “Matsuribare”, had weak tolerance. In the medium heading variety group, five varieties, “Otentosodachi”, “Koganemasari”, “Nikomaru”, “Shinrei” and “Hinohikari”, were selected as strong, moderately strong, middle, moderately weak and weak tolerance to high temperature, respectively. In the late and very late heading variety group, three varieties, “Nishihikari”, “Tachiharuka” and “Akisayaka”, were selected as moderately strong, moderately weak and weak tolerance to high temperature, respectively. High temperature tolerance of newly developed cultivars and lines in Kyushu region would be evaluated by observing grain quality after high temperature treatment at the ripening stage in comparison with standard varieties selected in this study.