Varietal Differences in Photosynthetic Rates in Rice Plants,with Special Reference to the Nitrogen Content of Leaves

Abstract

The photosynthetic rate in the fl ag leaf of rice at the full heading stage was examined in three japonica varieties, Koshihikari, Aikoku and Asanohikari, and the indica high-yielding variety Takanari at the same level of leaf nitrogen. At an ambient CO₂ concentration of 350 µL L-₁, Takanari had a higher photosynthetic rate and stomatal conductance than the japonica varieties when plants were compared at a leaf nitrogen content of approximately 1.5 g m-₂. Stomatal conductance increased considerably with increases in leaf nitrogen content in the japonica varieties. As a result, at a leaf nitrogen content of approximately 2.0 g m-₂, differences in terms of the photosynthetic rate among varieties were small. By contrast, there were no clear varietal differences in Rubisco content at any identical nitrogen content of leaves. We conclude that stomatal conductance is responsible for the varietal differences in photosynthetic rate examined at the same leaf nitrogen content.     

Response of Leaf Photosynthesis to Vapor Pressure Difference in Rice (Oryza sativa L) Varieties in Relation to Stomatal and Leaf Internal Conductance

Abstract

In the afternoon when air humidity decreases, leaf photosynthetic rate (P_n) often declines in rice grown under irrigated conditions. To clarify the genotypic difference of P_n in response to humidity, we measured P_n and stomatal conductance (g_s) for nine rice varieties with diverse genetic backgrounds, at various vapor pressure differences (VPD) and developmental stages. P_n and g_s of all the varieties decreased with VPD increase from 1.0 to 2.3 kPa of VPD. The variety with high g_s at low VPD exhibited a greater decline of g_s with VPD increase than the variety with low g_s, but cv. Takanari showed the highest g_s under altered VPD conditions. Significant logarithmic relations were found between the decreased P_n and g_s at the respective developmental stages, suggesting that g_s is the dominant factor determining P_n and its response to VPD change. To explicate the effect of decreased g_s on P_n, we analyzed the relations by using the model that accurately estimated the genotypic difference in P_n at a low VPD with g_s and leaf nitrogen content per unit leaf area in the previous study. The model assuming that leaf internal conductance (g_w) remains unchanged well explained the decreased P_n at high VPDs by g_s change alone. The analysis also suggested the constancy of g_w and carboxylation capacity at high VPD. It is concluded that the genotypic difference in the decrease of P_n at a high VPD is brought mainly by that in decreased g_s, and the varieties with a high g_s always exhibit a high P_n owing to their relatively high g_s at either high or low VPD environments.     

Response of the leaf photosynthetic rate to available nitrogen in erect panicle-type rice (Oryza sativa L.) cultivar,Shennong265

Increasing the yield of rice per unit area is important because of the demand from the growing human population in Asia. A group of varieties called erect panicle-type rice (EP) achieves very high yields under conditions of high nitrogen availability. Little is known, however, regarding the leaf photosynthetic capacity of EP, which may be one of the physiological causes of high yield. We analyzed the factors contributing to leaf photosynthetic rate (P_n) and leaf mesophyll anatomy of Nipponbare, Takanari, and Shennong265 (a EP type rice cultivar) varieties subjected to different nitrogen treatments. In the field experiment, P_n of Shennong265 was 33.8 μmol m^?2 s^?1 in the high-N treatment, and was higher than that of the other two cultivars because of its high leaf nitrogen content (LNC) and a large number of mesophyll cells between the small vascular bundles per unit length. In Takanari, the relatively high value of P_n (31.5 μmol m^?2 s^?1) was caused by the high stomatal conductance (g_s; .72 mol m^?2 s^?1) in the high-N treatment. In the pot experiment, the ratio of P_n/C_i to LNC, which may reflect mesophyll conductance (g_m), was 20–30% higher in Nipponbare than in Takanari or Shennong265 in the high N availability treatment. The photosynthetic performance of Shennong265 might be improved by introducing the greater ratio of P_n/C_i to LNC found in Nipponbare and greater stomatal conductance found in Takanari.     

Characterizing leaf gas exchange responses of cotton to full and limited irrigation conditions

Plant responses to water deficit need to be monitored for producing a profitable crop as water deficit is a major constraint on crop yield. The objective of this study was to evaluate physiological responses of cotton (Gossypium hirsutum) to various environmental conditions under limited water availability using commercially available varieties grown in South Texas. Soil moisture and variables of leaf gas exchange were measured to monitor water deficit for various varieties under different irrigation treatments. Lint yield and growth variables were also measured and correlations among growth parameters of interest were investigated. Significant differences were found in soil moisture, leaf net assimilation (A_n), stomatal conductance (g), transpiration rate (T_r), and instantaneous water use efficiency (WUE_i) among irrigation treatments in 2006 while no significant differences were found in these parameters in 2007. Some leaf gas exchange parameters, e.g., T_r, and leaf temperature (T_L) have strong correlations with A_n and g. A_n and WUE were increased by 30–35% and 30–40%, respectively, at 600 μmol (CO₂) m⁻² s⁻¹ in comparison with 400 μmol (CO₂) m⁻² s⁻¹. Lint yield was strongly correlated with g, T_r, WUE, and soil moisture at 60 cm depth. Relative A_n, T_r, and T_L started to decrease from FTSW 0.3 at 60 cm and FTSW 0.2 at 40 cm. The results demonstrate that plant water status under limited irrigation management can be qualitatively monitored using the measures of soil moisture as well as leaf gas exchange, which in turn can be useful for describing yield reduction due to water deficit. We found that using normalized A_n, T_r, and T_L is feasible to quantify plant water deficit.     

Differences in lamina joint anatomy cause cultivar differences in leaf inclination angle of rice

ABSTRACT

Leaf erectness is an important agronomic trait for improving canopy photosynthesis in rice. It is well known that leaf inclination angle (LIA) decreases after expansion during ripening. However, the high-yielding indica cultivar ‘Takanari’ retains a greater LIA during ripening than the high-quality japonica cultivar ‘Koshihikari’. To clarify the cause of the cultivar difference in LIA, we investigated anatomical characteristics of the lamina joint of a flag leaf. We found a close linear correlation between LIA at the centre and at the base of the leaf blade in both cultivars during ripening. The length of the lamina joint increased significantly more on the adaxial side of a leaf (the margin of the collar) than on the abaxial side (the abaxial side of the central part of the collar) in ‘Koshihikari’ after leaf expansion, but there was no clear difference in ‘Takanari’. We found a close linear correlation between the ratio of lamina joint length on the adaxial to abaxial sides and LIA in ‘Koshihikari’ and ‘Takanari’ during ripening. In ‘Koshihikari’, the average length of cells on the adaxial side increased significantly after leaf expansion, with no significant increase in that on the abaxial side and no significant change in cell number on either side. In ‘Takanari’, cell length and cell number showed no significant changes on either side of the lamina joint. We conclude that the cultivar difference in LIA during ripening is caused mainly by cell elongation on the adaxial side of the lamina joint.

List of Abbreviations: k: light extinction coefficient; LIA: leaf inclination angle; QTL: quantitative trait locus     

Analysis of yield attributes and crop physiological traits of Liangyoupeijiu,a hybrid rice recently bred in China

Crop physiological traits of Liangyoupeijiu, a “super” hybrid rice variety recently bred in China, were compared with those of Takanari and Nipponbare in 2003 and 2004 in Kyoto, Japan. Liangyoupeijiu showed a significantly higher grain yield than Nipponbare in both years, and achieved a grain yield of 11.8 t ha⁻¹ in 2004, which is the highest yield observed under environmental conditions in Kyoto. Liangyoupeijiu had longer growth duration and larger leaf area duration (LAD) before heading, causing larger biomass accumulation before heading than the other two varieties. Liangyoupeijiu had a large number of grains and translocated a large amount of carbohydrates from the vegetative organ to the panicle during the grain filling period. The three yield components measured were panicle weight at heading (P₀), the amount of carbohydrates translocated from the leaf and stem to the panicle during the grain filling period (ΔT), and the newly assimilated carbohydrates during grain filling (ΔW). It was found that the sum of P₀ and ΔT were strongly correlated with grain yield when all the data (n = 8) were combined (r = 0.876**). However, there was no significant difference in the radiation use efficiency (RUE) of the whole growth period between Liangyoupeijiu and Nipponbare for both years. Even though the growth duration was shorter, Takanari, an indica/japonica cross-bred variety, showed a similar yield to Liangyoupeijiu in both years. The mean RUE of the whole growth period was significantly higher in Takanari, 1.60 and 1.64 g MJ⁻¹ in 2003 and 2004, respectively, than in Liangyoupeijiu, which had a RUE of 1.46 and 1.52 g MJ⁻¹ in 2003 and 2004, respectively. The high grain yield of Takanari was mainly due to its high RUE compared with Liangyoupeijiu and its large P₀ and ΔT. Our result showed that the high grain yield of Liangyoupeijiu was due to its large biomass accumulation before heading, which resulted from its large LAD rather than its RUE.     

The QTL Analysis of RuBisCO in Flag Leaves and Non-Structural Carbohydrates in Leaf Sheaths of Rice Using Chromosome Segment Substitution Lines and Backcross Progeny F2 Populations

Abstract

In rice (Oryza sativa L.), the maintenance of high photosynthetic rate of flag leaves and the carbon remobilization from leaf sheaths after heading is a critical physiological component affecting the yield. To clarify the genetic basis of RuBisCO content of the flag leaf, a major determinant of photosynthetic rate, and non-structural carbohydrate (NSC) concentration in the third leaf sheath at heading, we carried out quantitative trait loci (QTL) analysis with 39 Koshihikari/Kasalath chromosome segment substitution lines (CSSLs) and backcross progeny F₂ population derived from target CSSL holding the QTL/Koshihikari in the field. QTLs for RuBisCO content and NSC concentration at heading were detected between R2447-C1286 and R2447-R716 on chromosome 10, respectively, by comparing Koshihikari with four CSSLs for chromosome 10 (SL-229, -230, -231 and -232). The progeny QTL for RuBisCO content and for NSC concentration at heading qRCH-10 and qNSCLSH-10-1, respectively, were detected at similar marker intervals between RM8201 and RM5708. In addition, QTLs for RuBisCO content at 14 d after heading, qRCAH-10-1 and qRCAH-10-2, were detected in regions different from that of qRCH-10. No QTL for NSC concentration at 14 d after heading was detected between RM8201 and R716, the region analyzed in this study. The QTLs qRCH-10 and qRCAH-10-1 for RuBisCO content would have additive effects. These QTLs for RuBisCO content and NSC concentration newly found using CSSLs and their backcross progeny F₂ population should be useful for better understanding the genetic basis of source and temporary-sink functions in rice and for genetic improvement of Koshihikari in terms of their functions.     

Perennial O. sativa × O. rufipogon interspecific hybrids: I. Photosynthetic characteristics and their inheritance

A survey of 24 wild Oryza accessions identified Oryza australiensis and Oryza rufipogon as potential sources of enhanced photosynthetic rate for introgression into cultivated rice. Photosynthetic capacity per unit leaf area (CER) was associated with leaf N content but not with leaf chlorophyll concentration, flag leaf area, or specific leaf area. Eight fertile, perennial F₁ hybrids between O. sativa and O. rufipogon were grown in non-flooded soil, and CER was measured at flowering under saturating light. Two F₁ hybrids had greater CER than the average of 26.1 μmol m² s⁻¹. The F₂ progeny from these hybrids were screened for CER in the field, and segregants with even greater rates of photosynthesis were selected. The basis of high photosynthetic rate in the F₂ populations was not leaf thickness or leaf chlorophyll content. One F₂ line had exceptionally high CER and stomatal conductance. Broad-sense heritability on an individual plant basis for CER in two F₂ populations was 0.44 and 0.37. A highly significant offspring-parent regression of 0.89 for CER was observed in a replicated field evaluation (four blocks, five plants per plot) of 20 vegetatively propagated F₂ selections and their F₃ seedling progeny. Broad-sense heritability for CER on a plot-mean basis was estimated as 0.74 for both selected F_2:3 families and for the selected F₂ clones. Genetic resources in the genus Oryza may represent a source of alleles to increase leaf photosynthetic rate in the cultivated species, which we have demonstrated to be a heritable, though environmentally variable, trait in an O. sativa/O. rufipogon population.     

Growth and Physiological Performance of Aerobic and Lowland Rice as Affected by Water Stress at Selected Growth Stages

Aerobic rice technology is still new in Malaysia, and information regarding MARDI Aerob 1 (MA1), the first local aerobic rice variety, is still lacking. Therefore, comparative studies were carried out to determine the physiological performance of aerobic rice variety MA1 and lowland rice variety MR253 under water stress given at the panicle initiation, flowering and ripening stages. This experiment was arranged in a randomized complete block design. Stomatal conductance (g_s), chlorophyll a fluorescence (F_v/F_m), leaf relative water content (leaf RWC), and soil moisture content (SMC) as well as yield component parameters such as panicle number, grain yield and 100-grain weight were measured. Results revealed that g_s and leaf RWC for both varieties decreased with depletion of SMC. The correlation study between the physiological parameters and SMC indicated that F_v/F_m was not affected by water stress, regardless of varieties. The yield components (panicle number, grain yield and 100-grain weight) for both varieties greatly decreased when water stress was imposed at the panicle initiation stage. This study showed that the panicle initiation period was the most sensitive stage to water stress that contributed to a substantial reduction in yield for both varieties. Under the aerobic condition (control), MR253 produced higher panicle number, 100-grain weight and yield than MA1. Although MR253 is bred for lowland, it is well adapted to aerobic condition.     

Genotypic Variation of Stomatal Conductance in Relation to Stomatal Density and Length in Rice (Oryza sativa L.)

Abstract

Stomatal conductance (g_s) is an important trait responsible for the genotypic difference in gas diffusion for photosynthesis and transpiration in rice (Oryza sativa L.). We measured g_s, stomatal density and stomatal length (guard-cell length) at two weeks before heading for 64 accessions from a rice diversity research set of germplasm (RDRS) and for three high-yielding cultivars (HYC) under field conditions. Considerable variations in g_s, and stomatal length were observed among varieties in RDRS, and it was considered that RDRS covers the species diversity of the stomatal characteristics in rice. When it was compared among the varieties with similar plant earliness, g_s was higher in HYC than in most varieties of RDRS. Stomatal density did not correlate with g_s, and there was a negative correlation between stomatal density and stomatal length. However, noticeable variance existed in the latter relation, where HYC exhibited a higher stomatal density and slightly shorter stomatal length than RDRS. High g_s in HYC is attributable to their high stomatal density and moderate specific stomatal conductance (g_s / stomatal density) while the high-g_s varieties in RDRS tended to have a lower stomatal density and higher specific stomatal conductance. Stomatal length is related to specific stomatal conductance, but there are remarkable differences between these traits. Specific stomatal conductance in HYC has not reached the upper limit for their stomatal size, which raises a possibility of further improvement of HYC in g_s.     

Varietal differences in tiller and panicle development determining the total number of spikelets per unit area in rice

ABSTRACT

Rice varietal differences were compared between japonica type (JAT) and indica type (INT) and between panicle number type (PNT) and panicle weight type (PWT) in terms of tiller and panicle development. Rice varieties PNT-JAT Hinohikari, PWT-JAT Akenohoshi, PNT-INT IR36, and PWT-INT Takanari were used in the field experiments. Tiller bud formation and tiller leaf emergence occurred slightly later in the PWT than in the PNT varieties. These parameters occurred slightly earlier in the INT than in the JAT varieties. The maximum number of tillers was greater in IR36 than in Takanari, Hinohikari, and Akenohoshi. The number of panicles per unit area (PN) was greater in IR36 and Hinohikari than in Akenohoshi and Takanari. The widths of the shoot apical meristem (SAM) just before panicle initiation were in the order of Akenohoshi > Hinohikari = Takanari > IR36. The number of spikelets per panicle (SN) was in the order of Takanari = Akenohoshi > IR36 > Hinohikari. In conclusion, the PWT varieties, which had relatively wider SAM, presented with the promotion of main shoot development and the suppression of tiller development. Consequently, PN decreased and SN increased in PWT varieties. INT varieties presented with the promotion of tiller and rachis branch development, which resulted in increases in both PN and SN. These developmental factors may determine varietal differences in the total number of spikelets per unit area.     

Leaf photosynthesis is enhanced in normal oil maize pollinated by high oil maize hybrids

The grain yield of normal oil maize (Zea mays L.) might increase when pollinated by high oil maize (HOM) hybrids because of heterosis. To testify that the grain yield increase might be a result of improved photosynthetic rate and related traits, the normal oil maize (NOM) hybrid, Nongda108, was cross-pollinated by three HOM hybrids, HOM202, HOM115 and HOM4515 (for short as ND108pHOM202, ND108pHOM115 and ND108pHOM4515). We found that the ND108pHOM202 and ND108pHOM115 exhibited higher net photosynthetic rate (P_n), accompanied by larger stomatal conductance (g_s) and transpiration rate (E). Moreover, delayed leaf senescence was observed in their leaves, including larger leaf area index (LAI) and higher Chl content and Chl a/b ratio. Apart from higher phosphoenolpyruvate carboxylase (PEPCase) activity, the soluble proteins were also higher in the two cross-pollinations. The higher leaf photosynthesis could explain the grain increase in ND108pHOM202 and ND108pHOM115. However, ND108pHOM4515 exhibited a decreased photosynthetic characteristic and yield performance. Significantly positive relation between grain yield and biomass (r² = 0.96, P < 0.05), P_n and biomass (r² = 0.74, P < 0.05) also suggested that the yield increase in the two cross-pollination treatments was generally owing to the higher photosynthetic rate and related photosynthetic traits.     

Genomic regions associated with the degree of red coloration in pericarp of rice (Oryza sativa L.)

The degree of red coloration (DRC) in pericarp of rice depends on the content of flavonoid compounds which have beneficial health effects for humans. In this study, 182 backcross-recombinant inbred lines (BILs) derived from Koshihikari (white pericarp)/Kasalath (red pericarp)//Koshihikari were used to detect the genomic regions associated with DRC through the QTL mapping approach. As a result, a total of four genomic regions were found to associate with DRC on chromosomes 1, 7, 9 and 11, respectively. Interestingly, the two genomic regions having the largest effects corresponded to previously characterized Rc and Rd genes on chromosome 7 and 1, respectively. In addition, two novel genomic regions having minor effects on DRC and located on chromosomes 9 and 11, respectively, are reported here for the first time. These results and the identification of tightly linked molecular markers that flank the genomic regions provide an opportunity for marker-aided improvement of red coloration in pericarp of rice.     

N applications that increase plant N during panicle development are highly effective in increasing spikelet number in rice

Efficient use of nitrogen fertilizer is critical in improving yield stability in rice. The objective of this study was to determine the effect of nitrogen (N) top-dressing on the number of total spikelet (fertile plus sterile) production and evaluate the effect among rice cultivars. We analyzed 136 sets of experimental data on growth and spikelet production for three lowland cultivars, grown under various regimes of N over 10 seasons at Kyoto, Ibaraki and Kanagawa, Japan. In each season, one to three of the lowland cultivars, Nipponbare (japonica), Koshihikari (japonica) and Takanari (indica), were studied. In 1986, 1995 and 1999-2001, the N regimes included basal application only, light basal and heavy top-dressing from the panicle initiation stage onward, heavy basal and heavy top-dressing from the spikelet formation stage onward, and no applications. In 2002 and 2005-2008, we set up experimental plots with varied time of N top-dressing, with or without N basal application. Takanari had the largest spikelet number averaged over all plots and was considered better efficient in spikelet production per applied N than the other cultivars. Although the trend is not clear, the effect of time of top-dressing on spikelet number was generally the greatest when N was top-dressed from 35 to 30 days before heading. The variation of observed spikelet number was analyzed with a linear regression of plant N 14 days before heading and by a model that estimates spikelet production accounting for plant N 14 days before heading and crop growth rate (CGR) during the 14-day period preceding heading. For the variation of spikelet number within each cultivar, the linear function model expressed the observed spikelet number than the two function model with R² 0.43** versus 0.13*-0.28** for the former and later models, respectively. When the results of all cultivars were combined, the two function model was much better for estimation of spikelet number than the linear function model (R² = 0.36** vs. 0.20*). This indicates that yearly and varietal variation of spikelet number was caused mainly by plant N status at the late spikelet differentiation stage. The varietal variation in spikelet production efficiency is explained by CGR during this 14-day period. We concluded that N applications that increase plant N 14 days before heading is highly effective in maximizing spikelet production among cultivars.     

The high yield of irrigated rice in Yunnan,China: ‘A cross-location analysis’

A number of field trials on rice productivity have demonstrated very high yield, but reported limited information on environmental factors. The objective of this study was to reveal the environmental factors associated with high rice productivity in the subtropical environment of Yunnan, China. We conducted cross-locational field experiments using widely different rice varieties in Yunnan and in temperate environments of Kyoto, Japan in 2002 and 2003. The average daily radiation throughout the growing season was greater at Yunnan (17.1 MJ m⁻² day⁻¹ average over 2 years) relative to Kyoto (13.2 MJ m⁻² day⁻¹). The average daily temperature throughout the growing season was 24.7 °C at Yunnan, and 23.8 °C at Kyoto. The highest yield (16.5 tonnes ha⁻¹) was achieved by the F1 variety Liangyoupeijiu at Yunnan in 2003, and average yield of all varieties was 33% and 39% higher at Yunnan relative to Kyoto in 2002 and 2003, respectively. There was a close correlation between grain yield and aboveground biomass at maturity, while there was little variation in the harvest index among environments. Large biomass accumulation was mainly caused by intense incident radiation at Yunnan, as there was little difference in crop radiation use efficiency (RUE) between locations. Large leaf area index (LAI) was also suggested to be an important factor. Average nitrogen (N) accumulation over 2 years was 49% higher at Yunnan than at Kyoto, and also contributed to the large biomass accumulation at Yunnan. The treatments of varied N application for Takanari revealed that the ratio of N accumulated at maturity to the amount of fertilized N was significantly higher at Yunnan than at Kyoto, even though there was no great difference in soil fertility. The Takanari plot with high N application showed a N saturation in plant growth at Kyoto, which might be related to low radiation and relatively high temperatures during the mid-growth stage. These results indicate that the high potential yield of irrigated rice in Yunnan is achieved mainly by intense incident solar radiation, which caused the large biomass and the N accumulation. The low nighttime temperature during the mid-growth stage was also suggested to be an important factor for large biomass accumulation and high grain yield at Yunnan.     

Genetic relationship between grain chalkiness,protein content,and paste viscosity properties in a backcross inbred population of rice

A backcross inbred line population derived from a cross between Koshihikari and Kasalath was used to dissect the genetic relationship among chalkiness, protein content, and paste viscosity properties in rice in three environments. A total of 11 traits (or parameters) were analyzed, including percentage of grains with chalkiness (PGWC), protein content (PC) and protein index (PI), and eight parameters from the viscosity profile. PGWC, PC and PI were significantly correlated with the paste viscosity parameters. We identified 39 QTLs in three environments; ten QTL clusters emerged. Eight QTLs were consistently detected across the three environments and further confirmed using a set of chromosome segment substitution lines (CSSLs) where Kasalath was used as the donor parent and Koshihikari as the recurrent parent. One and two major clusters on chromosome 6 corresponded to the Wx and Alk loci, respectively. The former was responsible for PGWC and most of the viscosity parameters, and the latter for PI and some viscosity parameters. Particularly, QTL qPI-6.1 was linked with both the Wx and Alk loci. The co-locations of QTLs for PGWC and viscosity parameters and the linkage of qPI-6.1 and qBDV-6 at the Wx locus could be largely responsible for the phenotypic correlations between these traits.     

Evaluation of the Effect of Photosynthesis on Biomass Production with Simultaneous Analysis of Growth and Continuous Monitoring of CO2 Exchange in the Whole Plants of Radish,cv Kosena under Ambient and Elevated CO2

Abstract

The effects of elevated CO₂ (approximate doubling of atmospheric CO₂ concentration) on the rate of photosynthesis estimated from continuous monitoring of CO₂ exchange in whole plants were investigated in radish cv. Kosena accompanied with simultaneous analysis of growth for 6 days from 15 to 21 days after planting (DAP). The elevated CO₂ increased the dry weights of hydroponically grown radish plants by 59% at 21 DAP.

The increase in dry weight was due to a combined effect of increased leaf area and increased photosynthetic rate per unit leaf area. Leaf area and the photosynthetic rate were increased by elevated CO₂ by 18-43% and 9-20%, respectively, during 15 to 21 DAP. Namely, an increase in the rate of photosynthesis is accompanied by an increase in leaf area, both having a significant effect on biomass production.     

Effects of yield-related QTLs SPIKE and GPS in two indica rice genetic backgrounds

Recent progress in rice genomics has promoted the identification of quantitative trait loci (QTLs) associated with yield and its related traits. SPIKE, a QTL controlling spikelet number per panicle, and GPS, a QTL controlling leaf photosynthesis rate, were identical to NAL1. To assess the effect of SPIKE/GPS on yield potential, we compared DNA sequences of these alleles and conducted yield experiments in the field of Japan using the near-isogenic lines NIL-SPIKE (allele from Daringan in IR 64 genetic background), NIL-GPS (allele from Koshihikari in Takanari genetic background), and a chromosome segment substitution line, SL2115 (allele from Koshihikari in IR 64 genetic background). Despite the two SNPs in the promoter regions between Koshihikari and Daringan, both alleles were effective to increase the number of spikelets per panicle both in Takanari and IR 64 backgrounds. However, the extent of the increase was smaller and unstable in Takanari background than that in IR 64 background. In addition, SPIKE/GPS improved percentage of filled spikelets only in the IR 64 background. These results suggest that the effects of SPIKE/GPS alleles are similar but are affected by the difference of the genetic backgrounds. Because the increasing effect of spikelets number per panicle was canceled by the decrease of the number of panicles, which seems to be affected by environmental factors, none of NIL-SPIKE, SL2115, or NIL-GPS significantly out-yielded their parental cultivars. These results indicate the importance to consider genetic backgrounds and QTL-environment interaction toward the future use of SPIKE/GPS.     

Performance of a High-Yielding Modern Rice Cultivar Takanari and Several Old and New Cultivars Grown with and without Chemical Fertilizer in a Submerged Paddy Field

Abstract

A high nitrogen-uptake capacity and effective use of absorbed nitrogen for dry matter and grain production are required to improve the production cost and environmental pollution. We characterized grain yield, dry matter production and nitrogen accumulation in six rice cultivars: Sekitori (released in 1848) and Aikoku (1882), referred to as SA cultivars hereafter; Koshihikari (1956); Nipponbare (1963) and Asanohikari (1987), referred to as NA cultivars hereafter; and Takanari (in 1990) as a high-yielding modern cultivar. The plants were grown with and without chemical fertilizer in a submerged paddy field. When plants were supplied with manure and chemical fertilizer, Takanari consistently produced the heaviest grain and dry matter, followed by the NA cultivars, and the SA cultivars the lightest. Dry matter production before heading was greater in Takanari and the NA cultivars due to the longer duration of vegetative growth. Dry matter production after heading was greatest in Takanari, with a larger crop growth rate (CGR), and smallest in the SA cultivars with a shorter ripening time. Greater dry matter production during ripening was accompanied by the greater accumulation of nitrogen by Takanari and NA cultivars. These plants developed a larger amount of roots. The smaller light extinction coefficient of the canopy was also attributed to the higher CGR in Takanari. When plants were grown without chemical fertilizer, Takanari also produced heavier grain and dry matter, followed by the NA cultivars. The heavier grain in these cultivars resulted from the greater dry matter production before heading, which was due to the longer period of vegetative growth. The greater dry matter production and nitrogen accumulation by Takanari and NA cultivars were evident when plants were grown with chemical fertilizer. Koshihikari was characterized by a higher CGR and greater nitrogen accumulation during ripening in the absence of chemical fertilizer which should be noted in efforts to decrease rates of nitrogen application.     

Variations in structural,biochemical, and physiological traits of photosynthesis and resource use efficiency in Amaranthus species (NAD-ME-type C4)

C₄ plants show higher photosynthetic capacity and productivity than C₃ plants owing to a CO₂-concentrating mechanism in leaves, which reduces photorespiration. However, which traits regulate the photosynthetic capacity of C₄ plants remains unclear. We investigated structural, biochemical, and physiological traits associated with photosynthesis and resource use efficiency in 20 accessions of 12 species of Amaranthus, NAD-malic enzyme-type C₄ dicots. Net photosynthetic rate (P_N) ranged from 19.7 to 40.5 μmol m^?2 s^?1. P_N was positively correlated with stomatal conductance and nitrogen and chlorophyll contents of leaves and was weakly positively correlated with specific leaf weight. P_N was also positively correlated with the activity of the C₃ enzyme ribulose-1,5-bisphoshate carboxylase/oxygenase, but not with the activities of the C₄ enzymes phosphoenolpyruvate carboxylase and NAD-malic enzyme. Structural traits of leaves (stomatal density, guard cell length, leaf thickness, interveinal distance, sizes of mesophyll and bundle sheath cells and the area ratio between these cells) were not significantly correlated with P_N. These data suggest that some of the biochemical and physiological traits are involved in interspecific P_N variation, whereas structural traits are not directly involved. Photosynthetic nitrogen use efficiency ranged between 260 and 458 μmol mol^?1 N s^?1. Photosynthetic water use efficiency ranged between 5.6 and 10.4 mmol mol^?1. When these data were compared with previously published data of C₄ grasses, it is suggested that common mechanisms may determine the variations in resource use efficiency in grasses and this dicot group.