The rice stink bug, which injures spikelets, has become a major pest in Japan and many other rice producing countries, as it reduces the quality and yield of brown rice by causing pecky rice and producing sterile grains. The area of stink bug infestation in Japan has increased as a percentage of the paddy rice planted area since the mid-1990s. By the early 2000s it was on a par with that of the major rice pests (green rice leafhoppers and small brown planthoppers) and has since become a serious problem. Methods to reduce stink bug damage such as management techniques for gramineous weeds that provide the habitat for stink bugs, chemical control techniques, and use of machines that specifically remove pecky rice, are costly and labor intensive. Therefore, it is desirable to breed rice cultivars that are resistant to rice stink bugs. Globally, research on breeding such resistant cultivars has achieved little progress. However, studies are being conducted to obtain resistant mother plants for breeding rice stink bug-resistant cultivars, to develop resistance assays for breeding, and to analyze the resistance mechanism. This review comprehensively discusses the current status of breeding for rice stink bug resistance and describes its future prospects.
Effects of cultivar and the environment in which the seeds were harvested on the seedling establishment after overwintering in early-winter direct-sowing cultivation of paddy rice were evaluated. We cultivated 60~72 combinations of cultivars and examined the effect of the environment in which the seeds were harvested on the seedling establishment after overwintering for three seasons at Iwate University. The observed seedling establishment range after overwintering was 0~64% in 2018/19, 0~33% in 2019/20, and 0~49% in 2020/21 depending on the combination of cultivar and the environment in which the seeds were harvested. The variation was relatively consistent over the years: there was a close correlation in seedling establishment between the years tested. An index of dormancy, the germination percentage measured on the 4th day after the start of incubation at 25°C in the germination test, was negatively correlated with the seedling establishment. This study provided a reference index to determine the appropriate dose of seeds to sow according to the cultivar and the environment in which the seeds were harvested for early-winter direct-sowing cultivation.
Steely grain rate is an important index for grain quality of hulless barley. The steely grain rate is evaluated by the ratio of the mealy and translucent areas in the endosperm on the cross-section of the grain. In this study, focusing on the difference in the transmittance between mealy and translucent endosperms, the non-destructive evaluation of steely grain rate using the brightness, an investigator of the transmittance, was developed, and then the accuracy of the method was validated. Ten sample sets of three cultivars collected in different years and fields with different split applications were prepared as calibration and validation sample sets. The regression line between the steely grain rate of the grain and the brightness adjusted by background had a significantly high coefficient of determination (R2) of 0.8709 (p<0.001) and was used for the prediction of the steely grain rate. The correlation between the measured and predicted steely grain rate of the grain was significant at p<0.0001, and the differences between the predicted steely grain rate and the measured one were less than 10 %. These results suggested that our proposed brightness measuring-based method allows high accuracy prediction of the steely grain rate. However, some sample sets collected in different fields from calibration samples showed significant differences in steely grain rates between measured and predicted values, suggesting that further improvement in accuracy is required.
The sweetness of ‘Kenroku’ sweet potato slices that are steamed and then dried rapidly decreases during the drying process. This rapid loss of sweetness could not be due to sugar degradation. We hypothesized that hardening of the slices concurrent with rapid drying decreases the sweetness release efficiency. The balance of these two opposing effects (increase in sugar concentration and decrease in sweetness release efficiency), both caused by drying, determines the optimal extent to which the slices should be dried in order to maximize the sweetness. We conducted repetitive simple sensory evaluations comparing pairs of slices dried at 30 °C for different drying times. In our experimental condition, maximal sweetness was achieved by drying the slices for 17 h. The drying time showed strong correlations with moisture content, hardness measured by the fruit hardness tester KM-1, and Brix of slices. The optimal values of these parameters were 30.6%, 0.89 kg, and 48.4%, respectively. Older subjects participating in the sensory evaluations tended to prefer the texture of existing products dried for more than 17 h, whereas younger subjects preferred the sweetest slices over the existing products. These results imply that sweeter and softer steamed and dried slices prepared with a shorter drying time than the existing products could appeal to a larger population and increase the demand of these products.
To reveal the sugarcane characteristics related to the adaptability to the mechanical harvesting-planting system using a cane harvester and billet planter, we compared the germination numbers (GN) and yields between the plots planted with harvester-prepared (HV) and manually prepared (control) setts of recommended varieties for Kumage-region. In 2017, GN and yields were lower in the HV-sett plots than in the control-sett plots in all varieties. In 2018, without rainfall for 2 weeks after planting, GN were considerably lower in the HV-sett plots than in the control-sett plots. Increase of planted bud numbers improved GN in the HV-sett plots, although the effect was less in the varieties with a larger stalk diameter. At harvest, the stalk numbers and yields were lower in the HV-sett plots, indicating that GN affected the yield through the stalk numbers. When the HV-setts were planted by a billet planter, GN, stalk numbers and yield of the variety ‘Harunoogi’, which showed thinner stalks, larger node numbers and higher germination rate, were highest. Although the variety ‘NiTn18’ showed the smallest GN, the yield was second-highest because of the compensatory tillering. These results indicated that the success of germination was most important in the mechanical harvesting-planting system, and that sugarcane characteristics such as thinner stalk and larger node number which contribute to the increase in bud number per unit weight of HV-setts, as well as higher germination and tillering abilities, were important for the adaptability to the system.
Summer buckwheat cultivation is expected to contribute to a stable production of high-quality, domestically produced buckwheat. However, the low yield is a serious problem. In this study, we examined the effects of foliar spraying of phosphite and micronutrients on the buckwheat yield and weed weight in farmers’ fields where buckwheat was sown from 30 March to 2 April, 2021. In experiment 1, the leaves were sprayed with phosphite on 17, 25 and 39 days after sowing (DAS). Foliar spraying of phosphite on 25 and 39 DAS, increased significantly at the 1% and 0.1% levels, the grain yield of buckwheat by 9.3 and 43.1 g/m2, respectively. In experiment 2, the leaves were sprayed with micronutrients on 17 DAS or with phosphite on 47 DAS. Foliar spraying of phosphite significantly increased at 0.1% level the grain yield of buckwheat by 38.2 g/m2, but spraying of micronutrients had no effect. In experiment 3, the leaves were sprayed with phosphite on 26, 40 and 47 DAS. The grain yield of buckwheat significantly increased from 18.7 g/m2 to 94.7 g/m2. Although the phosphorus and potassium contents of the soil before cultivation were appropriate, we discussed the hypothetical effects of a shallow hard soil layer and high groundwater level on phosphorus deficiency in buckwheat. Moreover, the foliar spraying of phosphite fertilizers did not increase the weight of weeds, which was a concern among the farmers. These findings suggested that the foliar spraying of phosphite fertilizers improves buckwheat yield.
Early-winter direct-sowing cultivation (EDC) is a cultivation method of sowing rice before the ground is covered with snow. We examined a management method to increase the emergence rate in EDC using rotary-tilling fertilizer application and a sowing machine in the Aomori Tsugaru area. In addition, the growth and yield were compared with conventional spring direct-sowing cultivation (CDC) in the 2018 and 2019 seasons. The snow-covered period was 120 days in 2018 and 69 days in 2019. The germination rate of the seeds collected from the field after the snow melted ranged from 55% to 88%, and tended to be lower in 2018 than in 2019. There was no significant difference between one-tilling without pre-tilling and two-tilling with pre-tilling. The emergence rate ranged from 29% to 60%. Setting the sowing machine to a seeding depth of 1 cm rather than 3 cm reduced the number of deeply sown seeds and increased the germination rate. Tamping soil in spring also improved the germination rate by 12%. The heading stage was 2 to 6 days earlier in EDC than in CDC. Under the conditions of surface fertilization during the budding season, there was no significant difference in yield between EDC and CDC. In simultaneous fertilization of sowing, EDC had fewer number of ears and lower yield than CDC. When supplied with additional fertilization, the number of paddies and yield were similar in EDC and CDC.