Rice crops growing under fluctuating soil water conditions in a rainfed field frequently experience severe photoinhibition at midday, potentially decreasing their biomass production. In this study, the long-term changes in midday photoinhibition in five rice cultivars growing under variable soil water conditions in a rainfed field were evaluated by determining the maximum quantum yield of photosystem II (Fv/Fm). Fv/Fm was generally lower under rainfed conditions than under flooded conditions at 65–75 days after sowing (DAS), but was similar under both conditions at 109–124 DAS. This mitigation of photoinhibition over time is likely an up-regulation of mechanisms to dissipate excess electrons, and an analysis of covariance showed that the degree of mitigation under the rainfed condition varied among the cultivars. Such genotypic differences in the long-term changes in Fv/Fm might be determined by the capacity of the cultivar to adapt to drought conditions.
The genotypic variation of oxidative damage under oxidative and drought stresses was evaluated for a total of 67 rice cultivars consisting of 61 from the rice diversity research set of germplasm and 6 high-yielding varieties. The maximum quantum yield of photosystem II (Fv/Fm) and the membrane stability index (MSI) were measured to assess the oxidative damage induced by methyl viologen (MV) for oxidative stress and polyethylene glycol (PEG) for drought stress. Considerable variations in Fv/Fm and MSI among the cultivars in MV treatment indicated the existence of genotypic diversity in the susceptibility to oxidative damage. The weak relationships of Fv/Fm and MSI between MV and PEG treatment suggested that mechanisms other than oxidative stress tolerance affected the genotypic diversity of oxidative damage in PEG treatment. We used principal component analysis to quantify the cross-tolerance to oxidative damage under MV and PEG treatments: cross-tolerance was higher in cultivars in the japonica group than in the indica groups and higher in the improved cultivars than in the landraces. These results suggest that genotypic diversity of cross-tolerance is related to adaptation to the ecosystem where the genotypes originated and that the characteristics responsible for the tolerance to oxidative damage have been selected during breeding for improved grain yield.
The inhibitory effect (allelopathic potential) of shoot, seed and root extracts of 8 white, 5 red and 5 black rice (Oryza sativa L.) cultivars was determined against the seedling growth of lettuce (Lactuca sativa L.) and white clover (Trifolium repens L.). All extracts inhibited hypocotyl and root growth of lettuce and white clover seedlings, and those inhibitory activities ranged from –1% – 96%. The average inhibitory activity of the extracts on the hypocotyl and root growth of lettuce and white clover was 42 – 88%. No apparent difference in the inhibitory activity was found either among the extracts of white, red and black rice, or among the extracts of shoots, seeds and roots. However, the red rice cultivar Tsushima-akamai marked the greatest inhibitory activity with an average of 88% growth inhibition on hypocotyls and roots of lettuce and white clover, followed by Souja-akamai and Koshihikari. These results suggest two red rice, Tsushima-akamai and Souja-akamai, may be potentially useful for weed management in agriculture.
Recently, the occurrence of chalky grain caused by high temperature stress at the ripening stage has been a global problem for rice. We previously showed that the deep and permanent irrigation method, which is the combination of the V-furrow direct seeding and deep-flood irrigation methods, reduced chalky grain occurrence. To study the possible physiological mechanisms for reduced chalky grain occurrence by the deep and permanent irrigation method, we conducted field experiments in 2008 and 2009 to examine the effects of the deep-flood treatment on plant nitrogen (N) content, stomatal conductance and photosynthetic rate especially at the ripening stage. Results showed that in the deep-flood treatment that maintained a 20 cm water depth, leaf N content was consistently and significantly higher than the control with only a 10 cm water depth. Except two measured days, the stomatal conductance under the deep-flood treatment was significantly higher than in the control. Furthermore, stomatal conductance and photosynthetic rate in the deep-flood treatment were always significantly higher than in the control in both years. Thus, the deep-flood treatment enhanced N uptake, and consequently photosynthetic activity, resulting in the reduction of chalky grain formation, as previously reported. Accordingly, the effects of deep- flood treatment on grain quality improvement in rice may possibly be attributed to the improvement in source activity.
Aerobic rice culture is a promising way to save water and achieve a high yield. The present study was conducted to identify the agronomic traits required for high rice productivity in aerobic culture using chromosomal segment substitution lines (CSSLs) obtained as progeny from the cross between Sasanishiki (japonica), as the recurrent parent and Habataki, a high-yielding indica cultivar with high spikelet production ability, grown under flooded and aerobic conditions in 2009 and 2011. Grain yields of the CSSLs in aerobic culture were similar to or higher than those in flooded culture in 2009, but were similar to or lower than those in flooded culture in 2011. There were significant effects of genotype and water environment on grain yield in both years. Most of the CSSLs had a higher grain yield than Sasanishiki in aerobic culture, whereas their average was close to that of Sasanishiki in flooded culture. Rice plants grown in aerobic culture had larger biomass production, which enabled most of the CSSLs to produce more spikelets per unit area and maintain single-grain weight, thereby producing a higher grain yield than Sasanishiki. These results suggest that high spikelet producing ability would promote high grain yield in aerobic culture.
Many trees are left uncut in the paddy fields of many villagers in central Laos. Yields of rice in rainfed paddy fields interspersed with trees in central Laos were investigated in relation to shading and soil fertility from trees. Grain yield of rice plants cultivated in close proximity to tree trunks (CTP) was higher than that of the plants cultivated far away from the tree trunks (FTP) in 5 fields but lower in 7 fields. The effects of individual trees on rice yield varied among trees of the same species over the course of the three-year study period. No relationship was observed between the changes in photosynthetic photon flux density (PPFD) due to interception by the tree and the ratio of grain yield of CTP to that of FTP. A significant negative relationship was observed between grain yield of FTP and the ratio of grain yield of CTP to that of FTP, suggesting that yield of CTP under some trees is not lower than that of FTP when the latter was low.
The contribution of cell wall components and nonstructural carbohydrate (NSC) to grain filling in rice (Oryza sativaL.) was clarified by investigating the differences in the dynamics of hemicellulose, sugar composition of hemicellulose, β-(1￫3),(1￫4)-glucan, and NSC among cultivars with different grain filling capacities. This investigation was performed using the stems of standard, high yield and low harvest index (HI) cultivars. Hemicellulose concentration in stems tended to decrease slightly during the grain filling stage. This decrease was attributed to a decrease in β-(1￫3),(1￫4)-glucan concentration, which was detected as a decrease in glucose composition of hemicellulose in the stems during the grain filling stage. The rate of decrease and decrease in the amount of β-(1￫3),(1￫4)-glucan in the stems differed among the cultivars. These were higher in high yield and high HI cultivars than in relatively low yield and low HI cultivars. Moreover, a positive correlation was observed between the rate of decrease in β-(1￫3),(1￫4)-glucan and NSC, indicating similarities in the dynamics of β-(1￫3),(1￫4)-glucan and NSC among the cultivars. When the top half of panicle was removed, β-(1￫3),(1￫4)-glucan and NSC concentrations in the culm and leaf sheath did not decrease during the grain filling stage. Therefore, the β-(1￫3),(1￫4)-glucan in stems might be one of the sources that supply substrate to panicle as well as NSC.
The effects of dry and wet preharvest periods on Hagberg falling number (HFN), a parameter of α-amylase activity, and rheological properties including farinograph dough development time (FDT), farinograph absorption (FA), resistance to extension (RE), loaf volume (LV) and baking score (BS) were examined in 30 hexaploid wheat (Triticum aestivum L.) cultivars originating from 19 countries. The cultivars were grown in the field in 2000–2010 and HFN and rheological properties were analyzed for three replicates. The cultivars were divided into three groups according to HFN in the wet preharvest period: HFN below 150 s (group H-1), HFN from 250 to 350 s (group H-2), and HFN over 400 s (group H-3). The cultivars in group H-3 were superior to those in either group H-1 or H-2 in all rheological properties except RE. In the dry preharvest periods, HFN was not correlated with rheological properties, while in the wet preharvest period HFN showed a highly significant positive correlation with FDT and BS. The canonical variate analysis for assessment of the general performance of all cultivars with HFN as the main factor and the other rheological properties as subfactors, indicated that the cultivars Stepnaja 30, Garazinko, Kirac, Klein Forten and Žitarka showed the highest potential regardless of preharvest rainfall amounts. In conclusion, differential genetic expression of resistance to preharvest sprouting, maintenance of low α amylase level, high HFN values, maintenance of rheological properties, and baking performance can be reliably detected and measured under wet preharvest conditions.
In this study, a deterministic algorithm named Ensemble Square Root Filter (EnSRF), an algorithm significantly improved from the Ensemble Kalman Filter (EnKF), was used to integrate remotely sensed information (ASD spectral data, HJ-1 A/B CCD and Landsat-5 TM data) with a wheat (Triticum aestivum L.) growth model (WheatGrow). The analyzed values of model variables, leaf area index (LAI) and leaf nitrogen accumulation (LNA), were calculated based on EnSRF without perturbed measurements. Independent datasets were used to test EnSRF and the root mean square error (RMSE) values were 0.81 and 0.82 g m-2, with relative error (RE) values of 0.15 and 0.13, for LAI and LNA, respectively. RMSE values for LAI and LNA were 1.39 and 1.70 g m-2, respectively (RE, 0.28 and 0.34) based on EnKF, 1.17 and 1.80 g m-2 (RE, 0.24 and 0.35), respectively, based on the WheatGrow model alone, and 0.97 and 1.25 g m-2 (RE, 0.21 and 0.24), respectively, based on the remote sensing models. These results indicated that the LAI and LNA values based on EnSRF matched the measured values well compared with the EnKF, WheatGrow and remote sensing models. In addition, the predicted results are consistent with the temporal and spatial distribution of winter wheat growth status and grain yields in the study area, with RE values of less than 0.2 and 0.1 for LAI and LNA, respectively. These results provide an important approach for simulating winter wheat growth status based on combining remote sensing and crop growth models.
A 7-year field experiment under a rice-wheat rotation system was conducted at Guanghan County in the Chengdu Plain of China from 2004 to investigate the long-term effect of different combinations of year-round tillage patterns and crop straw management on grain yield and quality of wheat. Treatments were rotary-till wheat+rotary-till rice without any straw (conventional treatment, CK), zero-till wheat with rice straw mulching+rotary-till rice with no wheat straw (WZRR), zero-till wheat with rice straw mulching+rotary-till rice with no wheat straw+autumn vegetable (WZRRV), zero-till wheat with rice straw mulching+zero-till rice with wheat straw mulching (WZRZ), and zero-till wheat with rice straw mulching+zero-till rice with wheat straw mulching under ridge-till (WRZB). There was little variation amongst years in grain yield and yield components with the treatment, while CK had lower yields in most years than other treatments with a slight decreasing trend; spike numbers per area had no significant change with the elapse of time. An obvious descending trend in grain number per spike and grains per area for CK and increase in 1000-grain weight for all treatments were observed; zero tillage and straw mulching improved wheat tiller ability, soil available nitrogen, phosphorus, and potassium contents at major growth stages, and leaf area index, SPAD, a portable chlorophyll meter reading, and dry matter at middle and late stages. Most grain quality traits of wheat were nearly the same in all treatments in all year-round tillage patterns.
Legume-grass mixed cropping may alleviate N starvation when incorporated as grass green manure which has a higher C/N ratio than legume manure. We focused on N and P absorption of oat in mixed cropping with hairy vetch, and investigated the effect of the mixed-cropping green manure on the growth and nutrient uptake of the succeeding corn. The total N and total P contents of oat mixed-cropped with hairy vetch were higher than those of sole-cropped oat, and dry weight in addition to N and P contents of oat were greatly increased by cutting mixed-cropped hairy vetch before blooming. Sole cropping of hairy vetch was the best green manure to enhance the growth and nutrient uptake of the succeeding corn crop, but mixed cropping of oat with hairy vetch was also highly effective. Further investigations are needed to determine the long-term effect of mixed cropping green manure on N and P sequestration as soil organic matter.