White-belly and white-core are the major two types of grain chalkiness in japonica rice. This study aims to compare the morphological features of white-belly and white-core using a scanning electron microcope (SEM). A japonica rice cultivar Wuyujing3 and its mutants were used as materials. Nearly 1000 SEM images were observed, and 12 representative photos were selected. SEM images showed contrasting differences between white-belly and white-core in endosperm microstructure including the shape of endosperm cell, the size distribution of starch granules, and the amount of protein bodies. White-belly and white-core also varied markedly in morphological features of the cracked compound starch granules. Our findings should help to advance our understanding of the multi-faceted nature of grain chalkiness from the perspective of starch and protein accumulation, and should be of value for future work on rice grain chalkiness.
Seed shattering is an important agronomic trait in rice as it directly affects the yield. Manipulation of the degree of shattering will maximize the yield potential. This study was performed to find an indicator for indirect selection to facilitate the selection of medium-shattering habit in japonica rice breeding. The grain shattering pattern and microscopic morphology of the separation zone on pedicels of five japonica rice cultivars with different shattering habits were compared. Almost all grains were separated between the sterile lemma and rudimentary glume in cultivars with medium-shattering, easily-shattering and very easily-shattering habits. On the other hand, approximately 50% of the grains of the cultivar with hardly-shattering habit were torn off at the bent portion of pedicel. A separation pileus was formed on the terminal of the pedicel. The pileuses were most prominent in cultivars with easily-shattering and very easily-shattering habits, while cultivars with a medium-shattering habit had more flat pileuses than prominent pileuses. Additionally, in the cultivar with a hardly-shattering habit all pileuses were flat. Development of fibrous cell walls on the separation pileus varied with degree of shattering habit. The easier the grain shattered, the poorer was the development of fibrous cell walls. These results strongly suggest that the shape of separation pileus and the development of fibrous cell walls are related to the shattering habit in japonica rice. Additionally, it is highly probable that the medium-shattering habit is characterized by the type of shattering that separates between sterile lemma and rudimentary glume with the flat shape of pileus.
The effects of gravistimulation direction on tuber formation and amyloplast distribution in the tuber tips of Chinese yam were investigated. Tubers placed vertically for either 2 or 14 d elongated in the direction of gravity vector. The subapical parts of tubers that were positioned horizontally for 2 d curved slightly toward the gravity direction, and such tubers elongated downward after 14 d. In tubers that were inversed for 14 d, the tips bent and eventually elongated in the direction of the gravity vector. These results indicated that the subapical part of the tuber was the initial site of curvature in response to gravistimulation. Microscopy and measurement of amyloplast sedimentation ratios showed that many amyloplasts sedimented downward in each tip cell of tubers that were placed vertically, inversely or horizontally. The results indicated that amyloplast sedimentation direction corresponded with the eventual direction of tuber elongation under different gravistimulation orientations. Tubers rotated at 90º intervals every day for 14 d did not have an elongating shape and grew multiple tips at different angles. In the rotated tubers, amyloplasts dispersed within the tip cells. These results showed that proper sedimentation of amyloplasts would be essential for the normal elongation and formation of tubers. The results of this study supported the possibility that sedimentable amyloplasts in the tuber tip were involved in gravity sensing and tuber formation.
Germination of rice (Oryza sativa L.) caryopses in the presence of exogenous ethanol (the end-product of alcoholic fermentation under anoxia) results in a decrease of coleoptile and root growth. The ethanol level measured in rice caryopses incubated in 50 mM exogenous ethanol under aerobic conditions was similar to that in caryopses incubated under anoxia. Application of 50 mM ethanol under aerobic conditions induced the production of OsFK2, a fructokinase isoform having a central role in the response of rice to anoxia. The induction of OsFK2 by ethanol was organ-specific: OsFK2 was produced mainly in the embryo and partially in the coleoptile, but not in root tissues. The results of this research suggest that rice can sense ethanol under anoxia and shows a molecular response to oxygen deprivation.
Aqueous methanol extracts of Bangladeshi rice (Oryza sativa L.) cultivar BR 17 inhibited the growth of roots and coleoptile of Echinochloa crus-galli extract-concentration dependently. The extracts were then purified by several chromatographic runs, and a phytotoxic active substance was isolated and identified by spectral analysis as (–)-3-hydroxy-β-ionone. The concentration of (–)-3-hydroxy-β-ionone in BR 17 was higher than that of two other phytotoxic substances, 9-hydroxy-4-megastigmen-3-one and 3-oxo-α-ionol, found in BR 17. The novel isolated (–)-3-hydroxy-β-ionone inhibited the growth of E. crus-galli at concentrations higher than 10 μM. Those phytotoxic substances may contribute to the allelopathic effect of BR 17. Therefore, the rice cultivar BR 17 may be potentially useful for weed management as a weed suppressing agent when incorporated into the soil or included in a rice-based cropping system.
Wet-seeded rice is a common method of sowing in Vietnam. Weeds, including weedy rice, however, are a major problem in this establishment method. A study was conducted in a farmer's field to evaluate the effect of pretilachlor dose (0, 300, 600, and 900 g ai ha–1) on the management of weedy rice and other weeds in wet-seeded rice cultivation in the spring-summer, summer-autumn, and winter-spring seasons of 2012-13. The herbicide was applied 1 day after sowing. Weeds belonging to the grass, broadleaf, and sedge groups were effectively controlled by the lowest herbicide dose (300 g ha–1). Overall, weed control did not increase with increases in herbicide dose after 300 g ha–1, suggesting the optimum dose for pretilachlor in wet-seeded systems. The application of pretilachlor at 300 g ha–1 significantly reduced the number of weedy rice panicles (20–69%) and weedy rice biomass (15–26%). The highest pretilachlor dose (i.e., 900 g ha–1), however, was better than the lower doses in reducing the number of weedy rice panicles (47–80%) and weedy rice biomass (41–54%). The non-treated plots produced a rice grain yield of 210, 2000, and 1850 kg ha–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. Compared with the non-treated plots, the lowest dose of pretilachlor improved grain yield. However, maximum yield was obtained by applying the highest dose of pretilachlor; 2690, 4490, and 5150 kg ha–1 in the spring-summer, summer-autumn, and winter-spring seasons, respectively. The results of our study suggest that a broad spectrum of weed flora can be easily managed by a lower dosage of pretilachlor in wet-seeded rice; however, the herbicide dose needs to be increased to 900 g ha–1 in order to decrease the weedy rice problem.
Direct seeding can curtail water and labor inputs involved in rice production; nevertheless, its large-scale adoption is impeded by heavy weed infestation. A field study was undertaken in 2011 and 2012 to evaluate the effects of crop row spacing (20 and 10 cm) and postemergence herbicides on weed growth and yield of dry-seeded rice. As a herbicide, pyrazosulfuron ethyl at 30 g ha–1, bispyribac-sodium at 30 g ha–1, or penoxsulam at 15 g ha–1 was applied (15 days after sowing, DAS) alone or in combination with fenoxaprop-p-ethyl at 86.25 g ha–1 subsequently (30 DAS). In addition, a partial weedy plot (manually weeded once at 28 DAS), and a weed-free plot were established for each row spacing In the partial weedy plot with 10-cm row spacing, the weed density was only 21 and 25% lower than that in the plot with 20-cm row spacing in 2011 and 2012, respectively. The sole application of an early postemergence herbicide restricted weed growth, while subsequent application of fenoxaprop as late postemergence application suppressed weed growth further, the magnitude of suppression being more pronounced in the plot with narrow row spacing. The density and biomass of weeds were lowest in the plot with 10-cm row spacing applied bispyribac-sodium followed by fenoxaprop . Under weed-free conditions, yields were 29% higher in the plot with 10-cm row spacing (4.18 t ha–1) than in that with 20-cm row spacing (3.23 t ha–1). Grain yield in the herbicide-treated plots was 87–188% higher than that in the partial weedy plots. These results suggested that narrow row spacing and sequential herbicide application can help tackle recalcitrant weed flora in dry-seeded rice fields.
The need for solar radiation (Rs, MJ m–2 d–1) estimation remains a common concern for agronomists. Evaluation of crop productivity is primarily based on Rs data, which are difficult to collect because of cost and calibration requirements. Generally, historical Rs data are more difficult to obtain. This study focused on an estimation model based on the daily range of temperature and evaluated its accuracy from the viewpoint of crop productivity analysis. The variability of an empirical coefficient in the model (KRs), which was derived from the relation between Rs and daily range of temperature (Tmax–Tmin) was analyzed using climatic data observed in Japan considering data availability and quality. KRs had significant monthly differences, and it significantly increased from 1981–1985 to 2003–2007 at all 10 locations. Period-month interactions were not significant, except for in Utsunomiya, suggesting that the seasonal pattern did not change during the period. Weather data indicated that the increase in KRs was caused not only by increased solar radiation but also by a decrease in Tmax–Tmin. The substantial differences in KRs produced considerable bias for the estimated Rs when the estimation was conducted with a constant KRs (0.16). Despite the bias, the model is considered to perform well given the present availability of Rs data. The results of this study suggest that the evaluation of the seasonal pattern of KRs greatly improves the model accuracy.
Despite the lack of scientific knowledge on plant density and its influence on component crops in intercropping, risk-averse smallholder farmers unabatedly continue growing crops in a mixture, which finally lowers the productivity of the system. Studies were conducted to evaluate the productivity, weed dynamics, nutrient mining, and monetary advantages in the maize-legume intercropping systems. The highest yield, maize equivalent yield (MEY), and per day productivity were recorded in the plot of sole cowpea (CP) and plots of maize (M) intercropped with CP at row proportions of 1:2 (1M:2CP) and 1M:5CP. Density and biomass of grasses, sedges, and broadleaved weeds were lowest in the plot of sole CP followed by 1M:5CP. Weed smothering efficiency was highest (88%) in the plot of sole CP followed by 1M:5CP, and lowest in the plot of 1M: 1frenchbean(FB) (8%). Nitrogen, phosphorus, and potassium were removed less by weeds by intercropping M with CP than with any other legume at row proportions of 1:5. Uptake of nitrogen and potassium was high in the plot of 1M: 5 blackgram (BG) The net return, net return per dollar of investment, and marginal returns were high in the plot of 1M:2CP followed by 1M:5CP. Intercropping M with CP at a row proportion of 1:2 gave a higher yield and nutrient uptake, and lowered nutrient mining by weeds with higher returns. In an area where weeds are the major competitor with M for site-specific resources, intercropping M with CP at a row proportion of 1:2 or 1:5 will help to suppress weeds and also to obtain higher MEY. Higher yield gave better returns. Inclusion of legumes increased the uptake of nutrients by maize. This intercropping system may be found efficient in similar situations or land use elsewhere, especially in Southeast Asia.
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