A deep root system may be a desirable plant characteristic in upland rice because it improves the plant's water extraction capacity. The objective of the present study was to assess the deep root development of rice cultivars in relation to soil moisture change and plant water status under upland conditions with moderate water deficits in the field and in simple lysimeter experiments. We used one upland cultivar ('Yumeno-hatamochi' [YHM]) and two lowland cultivars ('Lemont' [LMT] and 'Nipponbare' [NPB]) in the field experiment, with no supplemental water from 88 to 106 days after sowing (DAS) and 116 to 145 DAS. In the lysimeter experiment, we used YHM and NPB and imposed two water stress periods during the late vegetative stages (71 to 104 DAS and 88 to 104 DAS). In the lysimeter experiment, a higher deep-root length ratio (proportion of the length of deep roots to the total root length) in YHM was associated with a greater deep-root length than in NPB. The difference in deep root development was associated with change in soil water content at the depths of 45 to 70 cm between the two cultivars under the above conditions. The drought in the field experiment was less intense than in the lysimeter experiment, and we observed greater varietal differences in total aboveground biomass than in root system development; this was associated with the change in soil water content during the initial drought period. LMT, with smaller shoots, tended to save water and maintain higher leaf water potential and lower diffusion resistance as the drought progressed. Our results suggest that deep root development of rice was primarily advantageous for soil water extraction and plant water status under moderate water stress in uplands, but that the advantage of a deep root system was affected by total aboveground biomass, which had strong effects on plant water status under these conditions.
The partitioning of dry matter (ratio of dry weight of individual parts to that of total dry matter) was analyzed in snap bean cultivars, Haibushi, a heat-tolerant cultivar, and Kentucky Wonder, a heat-sensitive cultivar, at four temperatures after flowering on the subtropical island of Ishigaki, Japan. The temperature regimes included 27/23°C (day/night) as normal, 24/20°C as low, 30/26 as high, and 33/29°C as extremely high. Most growth traits increased after flowering time (35 DAS), displaying a plateau at 68-75 DAS. The total dry matter was similar under all temperature conditions, but differed with the cultivar. Haibushi had a higher value of total dry matter than Kentucky Wonder, which was mainly due to higher pod dry weight although stem and root dry weights were lower in Haibushi. A sharp decline of dry matter partitioning to pods was observed at 33/29°C. In the temperature range of 24/20 to 30/26°C, Haibushi showed higher partitioning to pods than Kentucky Wonder, independent of temperature. On the other contrary, Kentucky Wonder showed higher partitioning to pods at 27/23°C than at 24/20°C. These results showed that the partitioning of dry matter, which varied with the cultivar and temperature, played an important role in achieving higher harvest index in the heat-tolerant than in the heat-sensitive cultivars.
Seasonal wetlands, locally called oshanas, are characteristic of the densely populated northern Namibia, a desert country in southwest Africa. The formation of seasonal wetlands, which will sustain the water balance of a semiarid environment, was quite unstable depending entirely on the variable rainfall in the upper catchments of Angola. The objective of the present study was to evaluate the use of seasonal wetland water by pearl millet, the local staple food crop intercropped with cowpea, to discuss the water competition pattern of intercropped species. Root system development of the intercropped species was also evaluated together with the water source analysis. For this purpose, field experiments using pearl millet intercropped with cowpea in the seasonal wetland in Namibia University (Exp. 1) and monocropped pearl millet in the local farmers field (Exp. 2) were conducted in northern Namibia. Both pearl millet and cowpea developed deeper root systems as the distance from the seasonal wetland water increased. At flowering time, the δD value of intercropped cowpea was similar to that of wetland water, while that in pearl millet was much lower than those of both the wetland water and groundwater. This indicated that intercropped pearl millet did not have full access to the wetland water when there was competition with cowpea for water derived from various water sources. Under such circumstances, intercropped pearl millet probably relies more on the rainfall water, which is just sufficient to sustain its growth in a semiarid environment. By contrast, intercropped cowpea wins in the competition with pearl millet and can acquire water from the existing stored wetland water.
The leaf water relations, photosynthetic parameters and shoot growth of five snap bean cultivars were assessed during the drought period to determine their role in alleviating plant water deficit imposed by withholding irrigation at flowering. Soil water content of irrigated plants was 18-20% while that of unirrigated plants was 6-10% at 60 days after seeding (DAS). Leaf water potential was approximately 0.15MPa lower and relative water content was approximately 5% lower in unirrigated plants than in irrigated plants at 57 DAS. Unirrigated plants had a lower stomatal conductance (gs) and intercellular CO2 concentration (Ci). Reduced leaf water potential and relative water content were associated with a decreased stem elongation rate. Plants with a lower stem elongation rate had a higher specific leaf weight and succulence index (SucI). Significant differences among five cultivars of snap bean were found for all parameters measured. Decreased leaf water potential and stem elongation rate resulting from drought participated in preserving relative water content and improving specific leaf weight and SucI. Maintenance of higher relative water content increased gs and Ci. Cultivars that maintained a high relative water content when leaf water potential and stem elongation rate were decreased markedly, were more tolerant to drought than those which a reduced relative water content and the leaf water potential and stem elongation rate were only slightly lowered. Reduced yield (pods per plant and seed biomass) resulting from drought was associated with reduced relative water content.
The effects of phytohormones on the production of haploid wheat were examined in the intergeneric crosses between Japanese wheat cultivar(Triticum aestivum cv. Zenkojikomugi) and maize(Zea mays cv. Pioneer P80 Lisa). The detached wheat spikes pollinated with maize were cultured in a solution containing sucrose and sulfurous acid supplemented with 2,4—dichlorophenoxyacetic acid (2,4—D), indole-acetic acid, naphthalene acetic acid, kinetin or 6-benzylaminopurine at 0, 0.1, 1, 10, 100 or 1000 mg L-1.Haploid embryos obtained were cultured on agarose-solidified B5 medium.The frequency of plant regeneration was significantly affected only by the treatment with 100 mg L-1 2,4—D. Thus, the detached spikes were cultured in the medium containing 2,4—D at 0, 25, 50, 75, 100, 125, 150, 175, 200 or 400 mg L-1. The treatments with 50 mg L-1 2,4—D increased the embryo size, but the treatments with above 75 mg L-1 2,4—D inhibited the development of the embryo.The percentage of florets developing into haploid plants was increased by the treatment with 100 mg L-1 2,4—D. Therefore, the concentration of 2,4—D in the spikes treated with 2,4—D at 50, 100 and 150 mg L-1 were measured by gas chromatography.The concentration of 2,4—D in the seed was increased to 9.24 ppm by the treatment with 100 mg L-1 2,4—D, a further increase of 2,4—D concentration in the medium having no effect.On the other hand, the concentration of 2,4—D in the glumes and rachis increased up to 12.72 and 41.55 ppm by the treatment with 100 and 150 mg L-1 2,4—D, respectively.The treatments with 2,4—D at a concentration higher than 100 mg L-1 inhibited embryo development.The present results suggested that 2,4—D at the concentrations from 50 to 100 mg L-1 would be optimum for haploid wheat production using maize.
Northeast China produces an abundance of maize (Zea mays L.), and improvement of maize yield at this region correlates closely with ensure food supply safely of China. In recent years, deficiency or relative deficiency of potassium (K) in the soil is an important limitation to maize production. Maize inbred lines tolerant to K deficiency (T) and sensitive to K deficiency (C) were hydroponically grown in 1/2 Hoagland solution to study the possible mechanism of maize tolerance to potassium deficiency from physiological point of view. With the reduction of K+ concentration, DW of the plant became apparently greater in T than in C, the symptom of potassium deficiency advanced in C. Under K deficiency, the taproot elongation increased and root top ratio decreased to a greater degree in C than in T, C had fawer lateral roots. T had a stronger K+-uptake ability than C, and the difference was more obvious in culture solution with a lower K+ concentrations of culture solution. K+ dependent H+ extrusion from the root treated with K+ deficiency was larger in T than in C.
Mesembryanthemum crystallinum (common ice plant) was used as a model plant to study the regulatory properties of Crassulacean acid metabolism (CAM) and tolerance to abiotic stresses. Although transformation is a useful genetic approach, it has not been established in this species due to recalcitrancy for regeneration. To establish an efficient procedure for regeneration of M. crystallinum, we examined the effects of urea-type cytokinins, thidiazuron (TDZ) and forchlorofenuron (CPPU) on the adventitious shoot induction.Adventitious shoots were generated only from explants obtained from the cotyledonary node, not from explants obtained from the cotyledon, hypocotyl and roots. Urea-type cytokinins, TDZ and CPPU were more effective for the induction and the morphogenesis of adventitious shoots than adenine-type cytokinin, 6-benzyladenopurine (BA). We have found that the 2.5 mg L-1 TDZ induced the largest number of multiple shoots and the highest frequency of adventitious shoot induction from single explant. In addition, fewer hyperhydric shoots were produced on the medium containing TDZ than in that containing BA and CPPU in the presence of 1.0 mg L-1 NAA. The regenerated shoots rooted on the MS medium within one month, and the rooting was promoted by replacing the agar medium with vermiculite or Florialite. The fertile plant with normal morphological properties was harvested for four months after sowing. Using the improved regeneration procedure with TDZ, we successfully introduced a kanamycin-resistant gene (nptII-HPH) into the cotyledonary node mediated by Agrobacterium tumefaciens. These results indicated that this regeneration procedure using cotyledonary node explants and TDZ could be useful for the genetic engineering of M. crystallinum.
Even under extremely hot (40°C) conditions during anthesis, heat-induced floret sterility does not appear to be a serious issue for Australian rice growers. This contradicts previously reported temperature thresholds for floret sterility. To determine the factors associated with stable rice production under hot and dry conditions in the Riverina region of New South Wales (Australia), we examined rice (cv. 'Langi') pollination at different distances from the windward edge of a paddy field and its association with canopy microclimate. With an air temperature of 34.5C and a relative humidity of 20.7% during anthesis, poor pollination of florets occurred at the windward edge, but pollination remained stable farther from the edge. The temperature difference between the air and the panicles in the canopy reached as high as 6.8C under these conditions because of low humidity and strong transpirational cooling. Moreover, the length of the dehiscence at the base of the thecae during anthesis was long; this is a desirable trait for heat tolerance. The long basal dehiscence of the thecae of this cultivar and the lower panicle temperatures relative to the ambient temperature caused by high transpirational cooling appear to be the key factors responsible for stable pollination under the extremely high temperatures of the Riverina region.
To elucidate the genetic mechanisms underlying C3-C4 intermediate photosynthesis, we investigated the structural and photosynthetic characteristics of leaves of reciprocal hybrids between the C3-C4 intermediate species Moricandia arvensis (L.) DC. (MaMa) and the C3 species Brassica oleracea L. (cabbage; CC), which differ in genome constitution. Moricandia arvensis bundle sheath (BS) cells included many centripetally located chloroplasts and mitochondria, whereas those of cabbage had few organelles. Hybrid leaves were structurally intermediate between those of the parents and showed stronger intermediate C3-C4 features as the proportion of the Ma genome increased. The P-protein of glycine decarboxylase (GDC) was confined mainly to BS mitochondria in M. arvensis, but accumulated more in the mesophyll (M) of cabbage. In the hybrids, the accumulation of GDC in BS cells increased with an increasing Ma:C ratio. Hybrids exhibited gradients in structural and biochemical features, even in reciprocal crosses. The CO2 compensation point of reciprocal hybrids with high Ma:C ratios was lower than that of cabbage but higher than that of M. arvensis. Thus, the structural and biochemical features in hybrid leaves reduced photorespiration. Moricandia arvensis had a higher photosynthetic rate than cabbage, but the photosynthetic rates of hybrids were intermediate between those of the parents or comparable to that of M. arvensis. Our results demonstrate that the C3-C4 intermediate characteristics are inherited based on the ratio of the parent genomes, and that there is no evidence of cytoplasmic inheritance in these characteristics.
One hundred and thirty one clones of Zoysia spp. collected from 59 sites on the coasts of Taiwan and its neighboring islets were analyzed using both random amplified polymorphicDNA (RAPD) and isozymes to reveal their genetic variation. In the RAPD analysis with 12 primers, a total of 92 polymorphic bands which could distinguish 131 genotypes were found. There were 19 polymorphic bands and 81 zymogram patterns for esterase, and 9 bands and 10 patterns for acid phosphatase, respectively. Cluster analysis by the unweighted pair-group method with arithmetic means (UPGMA) of RAPD data indicated that clones collected from the same geographic region were clustered together. However, isozyme data showed discordant patterns. Interestingly, both RAPD data and isozyme fingerprinting revealed less correlation with the intuitive taxonomic classification of tested clones, but more related to the specific adaptation to the geographic or geologic aspects of their habitats.
Callus is an excellent source for in vitro plant regeneration, but plants regenerated from callus sometimes show phenotypic and genotypic variation from the initial plants. In this study, the variation in spikelet-related traits of the rice plants regenerated from calluses and their performance in the paddy field were examined. The phenotypic variation in spikelet-related traits of the regenerated plants was not always in a reduction in their mean value. For instance, panicle length, spikelet number and fertile spikelet number of Indonesian rice genotypes Ciapus and BP-140 in the regenerated plants were significantly greater than those of the initial plants (developed from the seeds). The spikelet fertility of the regenerated rice plants was not significantly lower than that of the initial plants except in Ciapus and BP-140. The occurrence of somaclonal variants varied with the genotype. Ciapus and BP-140, which induce many somaclonal variants, are suggested to be valuable for genetic, breeding or functional genomic studies, while Fatmawati, which is stable, could be used for genetic transformation study.
Waterlogging stress is an important limiting factor for wheat and barley production. Waterlogging tolerance was evaluated in the seedlings of seven species from the tribe Triticeae, including wheat, barley, durum wheat, rye (diploid and tetraploid), triticale, einkorn wheat, and Mizutakamoji (Agropyron humidum), to acquire basic information about their variation in waterlogging tolerance and to elucidate opportunities for genetic improvement of waterlogging tolerance in cultivated wheat and barley. The seedlings at the one leaf stage were subjected to waterlogging for 0 (Control: CT) or 12 days (Waterlogging: WT) in plastic cups (12 cm tall, 8 cm in diameter), and the morphological traits of shoots and roots were measured. Shoot dry weights (DW) of wheat (cv. Norin 61) and barley (cv. Benkeimugi) were lower under WT by 73% and 59%, respectively, than those in CT. Of all the evaluated genotypes, only A. humidum showed no reduction in shoot DW under WT. The relative shoot DW (W/C in shoot DW; proportion of shoot DW in WT to that in CT) was significantly correlated with relative root DW (W/C in root DW). The W/C in root DW correlated significantly with W/C in the number and length of adventitious roots, and with W/C in frequency of branching roots on the seminal root, suggesting that development of adventitious roots and branching roots under WT might be related to waterlogging tolerance in tribe Triticeae. The results of this study indicated that wild species of tribe Triticeae, such as A. humidum, might be useful resources to analyze waterlogging tolerance in cultivated wheat and barley.
We examined the contribution of polyphenols to the antioxidative activity in the grains of common buckwheat “Hitachi akisoba” (H) and “Kanto No.1” (K) and in those of Tartary buckwheat “Rotundatum” (R) and “Pontivy” (P). The antioxidative activity in the 80% ethanol extracts was 16.4 and 15.3 μmol-Trolox g-1 DW in H and K, respectively, and 52.9 and 57.4 μmol-Trolox g-1 DW in R and P, respectively. These extracts were analyzed by HPLC. In common buckwheat, (-)-epicatechin, (-)-epicatechingallate, and rutin were confirmed. The (-)-epicatechin content was 20.2 and 15.6 mg 100 g-1 DW, and those of rutin were 13.6 and 12.2 mg 100 g-1 DW in H and K, respectively. (-)-Epicatechin accounted for about 13 and 11% of the total antioxidative activity in H and K, respectively, and rutin about 2% in both varieties. Since each polyphenol accounted for only about one fifth of the total antioxidative activity, the existence of unknown antioxidants was suggested. In Tartary buckwheat, rutin quercitrin, and quercetin were confirmed. The rutin content was 1808.7 and 1853.8 mg 100 g-1 DW, in R and P, respectively. Rutin accounted for about 90 and 85% of the total antioxidative activity in R and P, respectively. Accordingly, rutin appears to be the major antioxidant in Tartary buckwheat.
In order to develop a cultivation technique for the practical use of phytoremediation of diesel-contaminated soil, we evaluated the rhizodegradation of diesel-contaminated soil using Italian ryegrass. Experiments were conducted under two different soil conditions that were expected to reduce the influence of diesel on the plant. Under the first condition, the initial diesel concentration which is expressed in the total petroleum hydrocarbon (TPH) concentration was set to 0.80%. The concentration was almost half the upper limit for the growth of Italian ryegrass. Under the second condition, zeolite was added to the experimental soil to improve the cation exchange capacity (CEC). In 152 days experiments, we evaluated the plant growth variables, TPH concentration, soil dehydrogenase activity (DHA) that is reflective of the rhizosphere microbial activity, and the aerobic bacterial count. The results suggest that the TPH concentration in first condition (0.80%) could not bring about a significant recovery of plant growth. The plant growth observed in first condition was equal to that observed in the case of the upper limit TPH concentration used in our previous study. However, under the second condition, it is suggested that the addition of zeolite could increase plant growth, which can in turn improve the rhizodegradation effect.
The supernodulating soybean cultivar Sakukei 4 was previously characterized by its superior capabilities of nitrogen (N) fixation and photosynthesis, and was expected to be high yielding. Since the N absorption by Sakukei 4 is largely dependent on N fixation, it may be strongly affected by waterlogging during the vegetative stage, which occurs frequently in major soybean producing areas. In this study, we investigated the reduced growth and yield resulting from waterlogging during vegetative stage and the subsequent recovery in Sakukei 4, in comparison with those in the normally-nodulating cultivar Enrei and non-nodulating genotype En1282. Under the field conditions, the reduction of growth and yield by waterlogging was greatest in En1282 among the three genotypes, indicating that capability of N fixation is essential for the recovery from waterlogging-induced injury. The waterlogging-induced yield reduction in Sakukei 4 resembled that in Enrei, although growth reduction was greater in Sakukei 4 than in Enrei. Irrespective of cultivar, the yield was associated more closely with the crop growth rate (CGR) during the post-treatment stage than with that during the waterlogging treatment. In the pot experiments, yields positively correlated with both above- and underground plant parts irrespective of cultivar, not significantly, but significantly with root dry weights in Enrei and with nodule dry weights in Sakukei 4. These results indicate that Sakukei 4 exhibits a marked decrease in dry matter production by waterlogging, but yield decrease is compensated to a level similar to that of Enrei because of its enhanced nodule growth during the recovery stage.
To quantify the effects of arbuscular mycorrhizal fungi (AM fungi) on the growth of upland field crops cultivated in Japan, we analyzed soil samples from 124 sites in 18 Japanese prefectures for available P content, pH and AM fungal spore density. The AM fungal spore density in the 124 soil samples was 1.7 per g DW on the average, and lower than 1.0 per g dry soil (DW) in about half of the soil samples. The maximum spore density was 20.6 spores per g DW. The density of AM fungal spore did not vary significantly with the sampling site and the kind of cultivated crop in the sampling field. The pH of the soil with a high spore density ranged from 6 to 8, and in the soil samples with a pH lower than 6 and higher than 8, the spore density was lower than 5 spores per g DW. Thus, in the acid or alkaline soil, the sporogenesis of AM fungi is suppressed. Because available P content was consistently low in the soil samples with a high spore density, P content was considered to correlate with the AM fungal spore density. Therefore, crop cultivation with limited P fertilizer application and reduced available P content may be important to increase AM fungal spore density in upland field soil.
Rice is the most important crop for supporting Cambodian economy, however the cultivated area is limited due to the rice production system. Rice is transplanted by hand and yet the direct-seeding technology and proper cultivars for direct-seeding have not been established. The aim of this study is to find the adaptability of Cambodian cultivars for direct seeding. First, we determined the seedling establishment of rice direct-seeded in a flooded paddy field, and examined their growth and yield. The seedling establishment of Koshihikari and W42 were significantly higher than those of Rumpe and Sen Pidao at both medium and low temperatures, but not significantly different among cultivars at high temperature. Koshihikari and W42 showed significantly higher seedling establishment than Sen Pidao at 0 cm deep sowing. And Koshihikari also showed significantly higher seedling establishment than both Rumpe and Sen Pidao at 1 cm and 2 cm deep sowing. The percentage of seedling establishment from the seeds sown after 4, 1 and 0 day of drainage was higher in Rohat than in the other cultivars. The percentage of seedling establishment in 0 day drainage was 51% in Rohat, but only 28% in Sen Pidao, which was the lowest among the cultivars. Cambodian rice cultivars had a short plant length and short basal low internodes, which contributed to strong lodging resistance. Crossing of Cambodian cultivars with Koshihikari to obtain cultivars adapted to direct-seeding in Cambodia was proposed.
Exploring approaches to optimizing spatial distributions of leaf area index (LAI) and leaf nitrogen content (LNC) should be useful for increasing grain yield in rice (Oryza sativa). The primary objective of this study was to characterize the variation of LAI and LNC distributions within the canopy in relation to grain yield and N uptake in rice. Two experiments with different N fertilization rates under conventional and intermittent irrigation (CI and II, respectively) were conducted in 2002 and 2003, using Japonica rice cultivar Wuyujing9. The results showed that grain yield and N uptake were significantly different among application rates of N (N rates), but did not differ between CI and II. LAI distribution at full heading was affected significantly by N rate but hardly by the irrigation method. Individual LAI increased with the N rate. To achieve a high yield, the proper distribution of LAI in the canopy can be designed as the largest in the 2nd leaf from the top, followed by the 3rd and 4th leaves, and the smallest in the top leaf. LNC on the base of both area and dry matter at 15 days after full heading decreased from the top to lower leaves in the canopy, and significantly increased with the N rate. Grain yield was enhanced linearly with the increasing N content of the upper two leaves, but hindered by the high N content of lower leaves. These results indicate that the spatial distributions of both LNC and LAI could be optimized to achieve maximum canopy photosynthesis and grain yield in rice.