In potato production, there is an increasing demand for smaller seed tubers. Dense plant cultivation or heat shock treatment is considered to produce small tubers. However, utilization of these methods is limited because of the high cost and the unstable effect. Therefore, in this study, we investigated whether small tubers can be efficiently produced by treatment of seed tubers with gibberellin (GA) using two different varieties. Application of GA increased the number of stems and yield of small tubers in both varieties. However, there was a significant difference in the response to GA treatment with the variety in various growth characteristics. The results suggested that the susceptibility to exogenous GA differed with the variety. GA is known to inhibit tuber initiation, and decrease the tuber weight at an early growth stage in highly susceptible varieties. However, in highly susceptible varieties, Application of GA increased the number of tubers at the harvesting period similar to that in less susceptible varieties. These results suggest that the nutrient competition among the tubers at the early growth stage was suppressed by GA treatment in highly susceptible varieties, so that the number of tubers at the harvesting period increased compared with the control. This study revealed that the treatment of seed tubers with GA increases the number of tubers at the harvesting stage in any variety irrespective of the susceptibility to GA.

We used two rice varieties for sake brewery, ‘Ginpuu’ and ‘Suisei’ to evaluate the effect of daily highest temperature on the annual variation of parameters of sake brewing aptitude in 2005–2013, in Hokkaido, Japan. The annual variation of white core rate (WCR) was the highest, and followed by that on crude protein content (CPC), 1000 grain weight (1000 GW), 20-minutes water absorption rate (20AR) and steamed rice water absorption rate (SAR). As daily highest temperature (DHT) from 19 to 10 days before heading (–II) rose, 1000GW in both varieties and WCR in ‘Suisei ’increased and CPC in ‘Ginpuu’ decreased. As DHT from 1 to 10days after heading (+I) rose, WCR in ‘Ginpuu’ decreased. As DHT from 11 to 20 days after heading (+II) rose, 1000GW increased and 20AR decreased in both varieties. As DHT from 21 to 30 days after heading (+III) rose, SAR in ‘Suisei’ decreased. Thus, we considered that the variations of DHT during –II influenced those of 1000GW in both varieties, CPC in ‘Ginpuu’ and WCR in ‘Suisei ’, that the variations of DHT during +I influenced those of WCR in ‘Ginpuu’, that the variations of DHT during +II influenced those of 1000GW and 20 AR in both varieties, and that the variations of DHT during +III influenced those of SAR in ‘Suisei’.

Resistance against wind-caused cane-top breakage is one of the important characteristics in sugarcane breeding in Japan, and it has been evaluated based on the breakage incidence in the field. However, a more reliable evaluation method is required because many unpredictable factors affect the breakage incidence. We previously found that the bending moment at breaking of the growth ring located about 50–60 cm below the highest dewlap showed a correlation with the breakage incidence in the field, suggesting it could be one of the candidate indexes for the resistance. In the present study, to verify the applicability of the bending moment at breakage as the index, we assessed its seasonal variation and varietal differences. The bending moment at breaking, section modulus and bending stress of 8 sugarcane clones were measured 3 times during the active growth stage. Measured bending moment at the breaking of each clone showed positive correlations between each measurement, and relative order among the clones was maintained. Result of the measurement of the section modulus and the bending stress indicated that the factor that mainly contributed to the high bending moment at breakage varied with the clone. In conclusion, the bending moment at breaking could be measured in a reproducible fashion, indicating that it was one of the useful indexes to evaluate the resistance against wind-caused cane-top breakage.

Rice seedlings sown at densities of 250 g and 300 g dry seeds per nursery box were grown for 15 or 24–25 days before being transplanted to the paddy field. From each high-density seedling mat, 3–4 seedlings per hill were planted with a rice transplanting machine, which was modified to pick a small area of the seedling mat. The plant age in leaf number of each seedling was 3.0–3.6 and the plant height was 8–12 cm at the transplanting time. Planting accuracy was high; the frequency of vacant hills was 0.0–6.3％ without consecutive blank hills. The number of high-density seedling mats required for transplanting was 4.7–7.2 per 10 a. The heading and maturity dates of high-density seedling were 1–2 days later than those of conventional seedlings. There was no significant difference between the crops grown from the conventional and high-density seedlings in terms of traits such as maximum tiller number, panicle number, grain yield, perfect grain ratio, and grain protein content. Judging from the height of seedlings in the nursery boxes and the increase in stem number after transplanting, the nursery management and transplanting time were considered suitable for late transplanting at a higher temperature. Use of high-density rice seedling mats, allowed to obtain high quality high yield rice without changing the conventional way of nursery management and using new nursery materials, except for the introduction of a new rice transplanting machine.