Considerable labor-saving in sugarcane planting work can be expected by introducing the billet planter which plants mechanically-harvested sugarcane setts. However, decrease in germination rate after planting due to physical damage on buds caused by mechanical harvesting is one of the major problems. In this study, characteristics of sugarcane varieties related to the number of undamaged buds after mechanical harvesting were investigated. Our survey on the conditions of the setts of recommended varieties for Kumage-region after mechanical harvesting revealed that 5-10% of buds were lost in all varieties, and that the varietal difference in damage rate in the remaining buds was not clear. On the other hand, the number of undamaged buds was larger in varieties with thinner stem and/or many nodes. Comparison of 2 varieties with different bud dormancy indicated that the germinated buds on standing stalks in the field were more susceptible to physical damage than the ungerminated buds. The number of damaged buds after mechanical harvesting was larger in NiTn18 compared to Harunoogi which had a higher rate of ungerminated buds than NiTn18. Furthermore, the number of damaged buds increased when stalks were detrashed. The results of the present study indicated that varieties with characteristics such as stalk thinness, larger node number, strong bud dormancy and difficulty of detrashing could be an advantage in suppression of mechanically-caused bud damage and in maintenance of undamaged bud number per weight of unit setts after mechanical harvesting.
The tolerance to high temperature during the treatment for disinfection in rice seeds is strengthened by reducing their water contents to below 10% before the hot water disinfection treatment. Pre-drying treatment prevents the reduction in germinability of the seeds disinfected with hot water at 65ºC for 10 minutes, which is a method used to effectively control several seed-borne diseases. We examined the conditions for pre-drying of seeds using a heating dryer for improving the germinability after the disinfection treatment. The seeds of Nipponbare were dried at 40 – 60ºC for 2 – 72 hours. A higher temperature was more effective for drying. When the seeds were dried at 40ºC, 12 hours of treatment was required to reduce the water content to below 10%. Thereafter, the water content rapidly decreased to around 8% by further heating, but the speed of decrease dropped and the values remained above 7% in the seeds dried for 24 hours at 50ºC. The germinability was not changed by further decrease in water content to less than 7%. In some cases, the seeds dried at 60ºC for 72 hours had lower germinability. Moreover, experimental results using Koshihikari showed that the seeds with a water content reduced to below 9.5% by pre-drying had a germination rate of more than 90%, even after the seeds were disinfected with hot water at 72ºC for 10 min. Taken together, we concluded that pre-drying to a water content of 7 – 9.5% in seeds at 40 – 50ºC for 12 – 24 hours is the most useful method for pre-drying the seeds of Nipponbare and Koshihikari before the hot-water disinfection treatment.
To avoid farm work competition and explore the possibility of diversification of cropping, we evaluated the yield and yield characteristics of the transplanting times (early, middle and late) in rice (Oryza sativa L.) for three years using three high-yielding cultivars, “Akidawara”, “Yamadawara” and “Toyomeki”, which have high eating quality. The later the transplanting time, the lower the filled brown rice yield. Sink capacity and the increase in shoot dry weight during grain filling tended to be smaller the later the transplanting time. To reveal the factors lowering the yield in late transplanting, we carried out several analyses under various climate conditions. The relationship between Y/S value, obtained from dividing yield (Y, g m–2) by cumulative solar radiation (S, MJ m–2) from 30 days before heading to 20 days after heading, and the average daily temperature in the same periods were approximated by a quadratic equation, meaning yield could be explained well by temperature and solar radiation. The maximum value in Y/S was found at around 23.4 to 24.0 ºC. On the other hand, it was inferred that the lower yield in late transplanting was affected not by the average daily temperature before and after heading but by the lower average daily solar radiation.
Low amylose rice exhibits strong stickiness and is still soft even after cooling. However, its low yield and lower molding efficiency because of the stickiness of the cooked rice during processing remained as problems. Here, we examined the effect of nitrogen application on the yield and eating quality of the low amylose rice cultivar, Kiraho, which was developed in Iwate Prefecture. The number of husks and the yield increased with the increase in the amount of nitrogen used for topdressing the crop. Regarding the texture of cooked rice, there was a positive correlation between the polished rice protein content (PPC) and the surface hardness of the cooked rice, and a negative correlation between the PPC and the surface adherence of the cooked rice. The increase in PPC after increasing the nitrogen for topdressing was suggested to reduce the stickiness of the cooked rice, an important factor during the molding process. However, there was no significant difference in the whole grain hardness of the cooked rice between different treatments of nitrogen topdressing, with the sensory evaluation showing only a small decrease in the overall eating quality. These results suggest that increase in the amount of nitrogen topdressing for the Kiraho cultivar improved its yield, modified the physical properties of the surface layer of the cooked rice by increasing the protein content and reduced the stickiness during processing, while hardly affecting the eating quality.
The resistance of rice genotype CRR-99-95W to the sorghum plant bug Stenotus rubrovittatus was investigated. In CRR-99-95W, the incidence of pecky rice caused by S. rubrovittatus decreased with the progress of ripening, as did that of the genotype, Aichinokaori SBL examined for comparison. At seven and 14 days after heading, the incidence of pecky rice was significantly lower in CRR-99-95W than in Aichinokaori SBL. At seven days after heading, the incidence of sterile grains was significantly lower in CRR-99-95W. These results indicated that in CRR-99-95W the incidence of pecky rice was suppressed in the early-middle stage of ripening and the incidence of sterile grains was suppressed in the early stage of ripening. Therefore, releasing the bugs to rice spikes at 14 days after heading, when pecky rice incidence is significantly high, is considered suitable for screening the resistance to S. rubrovittatus. We further examined the number of hill-cracked rice, which is highly susceptible to S. rubrovittatus. In CRR-99-95W, the number of hill-cracked rice increased under low temperature and low light conditions before heading, as in the genotypes examined for comparison. Since the number of hill-cracked rice in CRR-99-95W was the same as that in the genotypes examined for comparison, it can be inferred that the higher resistance of the former was not due to the presence of hill-cracked rice.
Three-year and two-year field experiments were conducted at the NARO Hokkaido Agricultural Research Center (NARO/HARC) (Sapporo) and its Bibai Experimental Station, respectively. Two rice cultivars, Yukigozen, bred in NARO/HARC and Nanatsuboshi, a common variety, were grown using a combination of two fertilization levels (standard fertilization and high fertilization) and two planting densities (standard density and low density). Yukigozen showed significantly higher grain yield in Sapporo in 2015, and significantly higher whole grain ratio in Sapporo in 2016 and in Bibai in 2018, than Nanatsuboshi. High fertilization gave a significantly higher grain yield only in Sapporo in 2015. In other years or in Bibai, fertilization rate affected neither grain yield due to lodging nor the trade-off between spikelet number per area and percentage of ripened grains nor grain weight. Low density resulted in significantly lower grain yield only in Bibai in 2018 with lower solar radiation. Yukigozen in standard density lodged with the nitrogen uptake at maturity more than 12 g m–2 or culm length longer than 80 cm, but that in low density had a lower lodging index. Yukigozen in low density tended to increase its grain yield by 28 g m–2 with high fertilization in Bibai in 2018. These results suggested that the combination of high fertilization and low density could reduce the risk of low grain yield under low solar radiation conditions and the risk of lodging caused by vigorous growth.