Global warming may reduce rice yield through poor pollination caused by high temperatures at flowering. The dominant parameter controlling the pollination stability in rice cultivars at high temperatures was studied. We examined the effects of a high daytime temperature (35.0ºC, 37.5ºC, 40.0ºC) and its duration (1, 3, 5 days) on the percentage of dehisced thecae, the length of dehiscence in the basal part of the theca for pollen dispersal, and pollination stability. The percentage of sufficiently pollinated florets (%SPF) decreased with the increase in daytime temperature and the duration of treatment. At a daytime temperature of 37.5ºC, %SPF varied widely among the cultivars and was highly correlated with the length of dehiscence formed at the basal part of the theca (r=0.930, P<0.01, n=6) and the percentage of dehisced thecae (r=0.868, P<0.05, n=6). The factor that better explained the variation in %SPF shifted from the length of the basal dehiscence to the percentage of dehisced thecae with increasing duration of high-temperature treatment. Thus, the process preventing pollination shifted from pollen release to anther dehiscence with the increase of exposure to a high temperature.
Consumer demand for good eating quality of cooked rice has been growing widely not only in Japan but also in other countries. Eating quality of the non-glutinous rice varieties bred in Hokkaido, northern Japan, during the past 20 years has improved drastically due to the breeding efforts focused mainly on chemical properties, such as amylose and protein concentrations. However, the effect of physical properties, such as cell morphology, on eating quality has been less studied. To clarify the relationship between physical properties and eating quality of rice, we investigated endosperm cell morphology (ECM) of grain by using a new simple method with a stereomicroscope for 18 non-glutinous varieties released over the past 100 years in Hokkaido. There were significant varietal differences in most of the ECM characteristics measured. Especially, cell density along the central line of endosperm (CLE) correlated negatively with the released year of varieties (r=–0.827, p<0.001), and decreased with the decrease in amylose and protein concentrations. The results indicated that the rice breeding in Hokkaido has changed not only the chemical but also physical properties. In addition, some varieties with similar amylose and protein concentrations showed large differences in CLE cell density. This suggests that the varietal difference in eating quality, which can not be explained by the difference in amylose and protein concentrations only, may be explained by the difference in CLE cell density. These findings will contribute to the further improvement in eating quality of non-glutinous rice.
To evaluate rice plant type precisely at the seedling stage, we established a quantitative evaluation method using an image analysis. P-type Fourier descriptors, which could apply an “open-curve”, were used for the plant type, and the coefficients were summarized as the scores of principal components (PCs) by principal component analysis. At the same time, “conventional plant type traits”, leaf blade length, leaf blade angle and inter-leaf-blade length, were measured by traditional plant type measurement methods. Based on the PC scores, the plant type for each PC was reconstructed by inverse Fourier transformation and the morphological characteristics were evaluated. To examine whether our method could appropriately identify the characteristics of the varieties, we discriminated the varieties using the PC scores by support vector machines. The varieties were also discriminated using the conventional traits of plant type. The results indicated that both traits had equal discrimination efficiency. In addition, the combination of conventional traits and scores had the highest discrimination efficiency. The relationship between the PC scores and conventional traits was examined by multiple regression analysis. The PC scores were not correlated with size-related traits. From these results, our research clarified that a plant type evaluation method using P-type Fourier descriptors could evaluate rice plant type precisely combined with conventional methods.
We examined the association of assimilate supply in the occurrence of milky white kernels in three cultivars with different percentages of milky white kernels in the field condition: ‘Hatsuboshi’, ‘Koshiibuki’ and ‘Koshihikari’. Five days after heading, the plants were placed in four controlled-environment chambers with either a high or low night temperature and elevated or normal [CO2] supply. Plants in each chamber were either defoliated with only flag leaf remaining, flag leaf and second leaf remaining or left intact (control). The percentage of each type of chalky kernel was examined. The percentage of milky white kernels was increased by defoliation and decreased by elevated [CO2], associated with assimilate supply. No association was observed between assimilate supply and white back or basal white kernels. The percentage of milky white kernels was negatively correlated with assimilate supply at a high night temperature in all cultivars. At a low night temperature, there was a clear threshold of assimilate supply, over which the percentage of milky white kernels was nearly zero. Cultivar differences were observed in the relation between the percentage of milky white kernels and assimilate supply. In conclusion, we found a varietal difference in the occurrence of milky white kernels in response to assimilate supply. In the cultivars used in this study, ‘Hatsuboshi’ was more sensitive to the low assimilate supply than ‘Koshihikari’.
The whole-leaf photosynthetic rate in rice plants is controlled by various physiological processes. In a high-yielding indica rice variety, Habataki, the leaf photosynthetic rate (LPR) of the uppermost fully expanded leaves was approximately 130 to 140% of that in a japonica variety, Sasanishiki, from booting to the early ripening stage. We characterized the difference in the LPR between Habataki and Sasanishiki. Leaves of Habataki contained higher levels of nitrogen and, as a consequence, of Rubisco, and had higher stomatal conductance that was associated with higher hydraulic conductance from roots to leaves than those of Sasanishiki. These features were responsible for the higher LPR of Habataki. An analysis of chromosome segment substitution lines (CSSLs) in which chromosome segments from Habataki were substituted into the genetic background of Sasanishiki showed that three genetic regions on chromosomes 4, 5 and 11 were responsible for the increase in the LPR. Each of these regions was estimated to increase the LPR by 15 to 30%, and we showed that they were associated with higher activity of mesophyll photosynthesis due to higher leaf nitrogen content and greater stomatal conductance. Leaf nitrogen content and stomatal conductance may be useful parameters for further quantitative trait locus analysis of efficient photosynthesis in leaves.
Aqueous methanol extracts of a traditional Bangladeshi rice cultivar (Oryza sativa L. cv. Kartikshail) inhibited root and shoot growth of cress (Lepidium sativum), lettuce (Lactuca sativa), alfalfa (Medicago sativa), timothy (Phleum pratense), crabgrass (Digitaria sanguinalis), Italian ryegrass (Lolium multiflorum), barnyardgrass(Echinochloa crus-galli)and jungle rice(Echinochloa colonum). The inhibition was increased with increasing the extract concentration, which suggests that cv. Kartikshail may have growth inhibitory substances and allelopathic potential. The aqueous methanol extract of cv. Kartikshail was purified and two main inhibitory substances were isolated and identified by spectral data as 3-hydroxy-β-ionone and 9-hydroxy-4-megastigmen-3-one. The concentrations required for 50% growth inhibition on cress roots and shoots, respectively, were 4.9 and 9.5 μM for 3-hydroxy-β-ionone, and 0.54 and 0.72 μM for 9-hydroxy-4-megastigmen-3-one. The concentrations required for 50% growth inhibition on barnyardgrassroots and shoots, respectively, were 160 and 310 μM for 3-hydroxy-β-ionone, and 53 and 140 μM for 9-hydroxy-4-megastigmen-3-one. The inhibitory activity of a mixture of the two compounds was much higher than that of the sum of the two compounds, suggesting that the two compounds may act synergistically to inhibit the growth of cress and barnyardgrass. The present research suggests that 3-hydroxy-β-ionone and 9-hydroxy-4-megastigmen-3-one may be responsible for the growth inhibitory effect of cv. Kartikshail and may play important roles in the allelopathy of cv. Kartikshail. The traditional Bangladeshi rice cultivar Kartikshail may be potentially useful for weed management as a weed suppressing agent when this rice cultivar is incorporated into the soil or included in rice-based cropping systems.
The changes in biomass production, root length, mineral nutrition, potassium absorption efficiency (KAE), and potassium use efficiency (KUE) of the halophytes Catapodium rigidum and Hordeum maritimum in response to potassium availability were assessed under natural conditions. Plants were cultivated in the greenhouse of the experimental station of the Biotechnology Centre of Borj Cédria (a Mediterranean coastal area) 30 km south-east of Tunis for four months from the autumn to winter of 2007–2008. H. maritimum biomass production was not significantly affected by the K+ concentration, but C. rigidum growth was increased significantly with increasing K+ concentration in the medium. Root/shoot dry weight ratio remained constant in C. rigidum, but decreased significantly at 1000 and 3000 µM K+ in H. maritimum. KAE increased but KUE decreased significantly with increasing K+ concentration in the medium in both species. However, KAE was higher in H. maritimum than in C. rigidum showing a contrasting response to K+ concentration between the two species. Overall, the maintenance of a cationic balance may be explained by cation antagonism. The lower K+ requirement of H. maritimum to express its optimal growth can be attributed to its higher efficiency to acquire and transfer K+ to shoots.
Autophagy appears to function in bulk protein degradation and N remobilization in senescence. Depodding of soybean suppresses N remobilization from leaves, leading to “green stem syndrome”. Expression of autophagy-related genes (ATGs) and N contents of the leaves and stem was analyzed in soybean plants from none (control), half (50% depodding) and all (100% depodding) of flowers and pods were removed at the reproductive 5 stage. Total N content and SPAD in leaves of the plant after 100% depodding were retained at a constant level and those after 50% depodding gradually decreased from 4 to 5 wk after depodding, while those in the control plants rapidly decreased during this period. Expression of GmATG8c and GmATG8iin leaves peaked at 4 wk in control while the gene expression increased gradually after 50% and 100% depodding. The transient up-regulation of ATGs and the decline of leaf N content and SPAD occurred simultaneously. These results indicated that ATGsare involved in leaf senescence and N remobilization from leaf to pod.
A low cadmium (Cd) concentration in wheat grain is desirable because of Cd toxicity to humans. Grain Cd concentrations in Japanese wheat differed among the varieties in previous study. In this study, we hypothesized that the varieties with a low concentration of Cd in grain have (1) low Cd uptake from the soil through the roots during early growth and/or (2) low Cd translocation from the roots to shoots, and also, that (3) Cd uptake from soil is affected by root morphology. These hypotheses were verified by investigating the concentration and quantity of Cd in root, shoot and leaf tissues, and examining the root morphology of young seedlings of wheat varieties with high and low grain Cd concentrations. Seedlings of ‘Kitahonami’ and ‘Nanbukomugi’ which had low grain Cd concentration (low Cd/G varieties) had a lower Cd quantity in whole plant tissues than ‘Nishikazekomugi’ and ‘Kitakamikomugi’ which had high grain Cd concentration (high Cd/G varieties) during early growth. Low Cd/G varieties also showed lower root to shoot (aerial parts) translocation of Cd than high Cd/G varieties. Seedlings of low Cd/G varieties showed less root branching than high Cd/G varieties. Root frequency showed a significant positive correlation with Cd quantity in whole plant tissues. These results suggest that low Cd/G varieties used in this study have low Cd uptake and translocation from the roots to shoots during early growth, and furthermore, that low Cd uptake at the seedling stage may relate to slow and/or limited development of branching roots.
We screened acid soil-tolerant wild soybean (Glycine soja Sieb. and Zucc.) accessions and evaluated their agronomic and tolerant performance under acid sulfate soil (ASS) conditions. Only three accessions, J-13, J-19 and J-55, among 381 G. soja accessions obtained from G. soja Germplasm Collection of Japan, were identified as having strong tolerance by the acid soil toxicity score (ATS) at soil pH 3.3. These three tolerant G. soja accessions showed significantly lower aluminum (Al), iron (Fe) and manganese (Mn) contents in the aboveground part than the intolerant ones in 0.25 lime requirement (LR) conditions (pH 3.8). Aboveground dry matter weights (DW) and seed yields of three tolerant G. soja accessions, except seed yield of a tolerant accession J-55, were also significantly higher than intolerant ones under the 0.25 LR condition. This clearly indicates that lower contents of toxic mineral in the ASS-tolerant G. soja led to higher macro-nutrient uptake, DW, and seed yields. We conclude that the three tolerant G. soja accessions identified in the present study possess high levels of tolerance to the soil acidity and Al-excess soil conditions, and could be valuable genetic resources for soybean improvement programs.
Amylose content was predicted by measuring tridimensional Commission Internationale de l‘Eclairage (CIE L*a*b*), L*a*b* values in starch-iodine solutions and building a regression model. The developed regression model showed a highly significant relationship (R2=0.99) between the L*a*b* values and the amylose content. Apparent amylose content was strongly and negatively correlated with L*a*b* values. This method could be used to predict amylose content in rice. The conversion of L*a*b* values to red, green, blue (RGB) values and to color hexadecimal codes allowed reproducing the colors of starch-iodine solution and making an explicit color board. Using this specific color board, we could sort entries into their respective classes and easily estimate their apparent amylose content.
The effects of planting time (early or normal), nitrogen (N) application rate (150 or 225 kg N ha-1), and N application method (early, even, and late application of extra N) on total digestible nutrient (TDN) concentration and yield of forage rice (Oryza sativa L.) in southwestern Japan were examined. For optimal forage rice production, it is important to maximize nutritional level in leaves and stems rather than panicles because the hull restricts cattle’s ability to digest rice grain. In particular, it is important to maximize the TDN in leaf sheath plus stems (stems) which are the major part of the crop rather than leaf blades (leaves). Stem TDN yield was higher with early planting (340 g m-2) than with normal planting (217 g m-2) irrespective of N application rate or method. The high stem TDN yield with early planting resulted from both the high DM yield and the high TDN and organic cellular content (OCC) concentration. Stem TDN yield was not affected by the N application rate. With both early and normal plantings, stem TDN yield was higher with early N application (374 and 226 g m-2, respectively) than with late N application (305 and 208 g m-2, respectively). With early planting, the high stem TDN yield with method 1 resulted from both the high DM yield and the high TDN and OCC concentration. Thus, to obtain high stem TDN concentration and yield of forage rice, early planting and early N application are recommended.
The chlorophyll meter (SPAD) has been widely used to measure the leaf N concentration. Nevertheless, linear regression equations of SPAD readings on N concentration (based on dry weight, Nw) differ with plant age and genotype mainly due to differences in specific leaf weight (SLW), and there is a close relationship between SLW and leaf thickness. This implies that SPAD readings may be influenced by leaf thickness alone. The present paper is to testify whether SPAD readings on rice (Oryza sativa L.) are influenced by variation in leaf thickness in different plant ages or genotypes. In a paddy field trial with rice Bing 9363 and in a lysimeter trial with 9 genotypes of rice, leaf thickness was measured using a specially developed displacement sensor. Leaf N was estimated using SPAD-502 and directly determined by Dumas combustion method. At 3 growth stages in the field trial, the degree of linear fit between Nw and SPAD values was poor (R2=0.557), but it was improved (R2=0.729) by introducing leaf thickness as an independent variable. In pooled data of the lysimeter trial, the predication of Nw was also improved by introducing leaf thickness as a secondary independent variable, the coefficients being increased from 0.0114 (not significant) to 0.513. However, if the leaf N concentration was expressed based on leaf area (Na), the leaf thickness did not influence the value estimated from the SPAD reading in both trials.
Rice is the single most important food crop in Laos. Savannakhet province, the largest area of rainfed lowland rice of any single province in the country was selected for the present case study to quantify the spatial distribution of two major limiting factors, water availability and soil fertility, and rice productivity in rainfed lowlands. Field water availability, fertilizer application and other crop management practices, and grain yield information were collected from over 100 farmers to provide basic information relating to rainfed lowland rice productivity and potential bio-physical constraints in this province over two rice cropping seasons. Poor soil fertility is identified as a major yield constraint with yield responding strongly to fertilizer application rate. The results also show that rainfall distribution pattern, soil type and position of rice fields on a sloping land, affect paddy water availability, and this in turn influences sowing time and is also expected to have effect on grain yield. To improve the productivity of rainfed lowland rice, combination of appropriate crop phenology, increased fertilizer use that is matched with water availability, and an understanding of soil water condition for the rice growing environment, is required. In a long term increasing soil fertility is required, and a significant improvement in rice productivity cannot be achieved by improved water availability alone, in a situation where the majority of paddy soils have low levels of fertility.
Crop production in a rainfed area is constrained by inappropriate management of soil and water by the resource-poor farmers. The present study addresses this issue through integration of practices for soil water conservation (SWC) and soil fertility enhancement as well. Extensive experimentation on wheat-maize was undertaken for two years (2004−2006) on the fields of eight farmers representing two soil types; Rajar (Typic Ustorthent; USDA soil taxonomy) and Guliana (Udic Haplustalf; USDA soil taxonomy) in the Gujar Khan Tehsil of Rawalpindi District, Pakistan. Four treatments consisting of: no SWC+farmer’s rate of fertilizer application (FP), no SWC+improved fertilizer application (IF), SWC practices i.e., deep plowing, bund improvement, plowing across contour+FP (SWC+FP) and SWC+IF. Wheat and maize grain yields in SWC and IF were statistically higher than in the treatments with no SWC and FP, respectively. Compared with the control without any treatment, increase in water use efficiency of both maize and wheat crop was higher in SWC+IF followed by IF alone. On the average, Guliana soil series showed better response to all treatments than Rajar soil. The integrated application of SWC and IF practices increased crop yields in the rainfed area.
Enhancement of nitrogen fixation activities by a cultivation technique is one of the potential targets to improve soybean yield in Japan. A cultivation technique named “crack fertilization” is described and the nodulation control by this technique is analyzed by experiments in two fields with different soil and environmental conditions, and a root box experiment. Crack fertilization is a technique that utilizes the irregularly shaped soil cracks formed by subsoiling just before the flowering stage of soybean, and introduces root nodule bacteria, fertilizers, and so on to the deep subsoil layer. Production of ureide-form nitrogen at six weeks after the crack fertilization (only nodule bacteria application to the subsoil layer) was 1.4 times higher than the control in the Hikone field. Acetylene reduction activity at four or eight weeks after the crack fertilization (application of both nodule bacteria and low level of fertilizer to the subsoil layer) tended to be higher than in the control in both fields. In the root box experiment, nodule number was four times higher than that in the control at the lower portion of the root system, where modified crack fertilization treatment was conducted, and the acetylene reduction activity was increased significantly by the treatment. These results indicated that the soybean nodulation control, i.e., timing and position of nodulation, as well as the enhancement of nitrogen fixation activity could be achieved by this crack fertilization technique.