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.     

Effects of Flag Leaves and Panicles on Light Interception and Canopy Photosynthesis in High-Yielding Rice Cultivars

Abstract

The effects of flag leaves and panicles on canopy photosynthesis in a leading cultivar (Nipponbare) and two high-yielding rice cultivars (Takanari and Ghugoku 117) bred in Japan were compared. The total dry matter production was in the order of Takanari > Ghugoku 117 > Nipponbare. Canopy photosynthesis was highest in Takanari throughout the growth season, and was higher in Chugoku 117 than in Nipponbare during the ripening period. The photosynthetic rate in the flag leaf was in the order of Nipponbare > Takanari > Chugoku 117. The light extinction coefficient of canopy was higher in Takanari than in the others. At the middle ripening stage, canopy photosynthesis increased 35 and 17% in Nipponbare and Takanari, respectively, by the removal of panicles and decreased 37 and 48%, respectively, by the removal of flag leaves. In Chugoku 117, canopy photosynthesis was hardly influenced by these treatments. Clearly, the panicles intercept more radiation at the upper layer of the canopy in Nipponbare than in Takanari and flag leaves contribute more to canopy photosynthesis in Takanari than in Nipponbare. However, these effects were small in Chugoku 117. In conclusion, Takanari produces more dry matter than the others due to larger, wider, longer and more erect 1st (flag) and 2nd leaves above the panicles, which intercept more radiation. Chugoku 117 had erect panicles which allowed more radiation to penetrate into the deeper layer of the canopy, resulting in a high dry matter production. The lower panicle height relative to leaf layer and erect panicles are important characteristics for higher yield in rice.     

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.     

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.     

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.     

Contribution of Nitrogen Absorbed during Ripening Period to Grain Filling in a High-Yielding Rice Variety,Takanari

Absract

High-yielding rice varieties require a large accumulation of N in panicles. The objectives of this study were to clarify the change in N allocation during the ripening period (Exp. 1) and to quantify the contribution of N absorbed during the ripening period to panicle N at maturity (Exp. 2) in the high-yielding variety Takanari in comparison with that in Nipponbare as a control. In Exp. 1, ¹⁵N-labeled N (¹⁵N) was applied at heading to investigate the distribution of newly absorbed N as well as the allocation of plant N. In Exp. 2, split ¹⁵N application was performed during the filling period to estimate the above contribution. In Exp. 1, the allocation of plant N and absorbed ¹⁵N to the panicles was larger and that to the leaves was smaller in Takanari than in Nipponbare during the ripening period, although Takanari accumulated more N at maturity. The difference in N allocation suggested that the difference in N demand in panicles would be larger than that in N uptake. In Exp. 2, the varietal difference in the grain filling duration was observed: Nipponbare accumulated little N in the panicles after 28 d after heading (DAH), while Takanari accumulated about a quarter of its panicle N during that time. An estimate showed that in Takanari, 13.5% of the panicle N was derived from N absorbed after 28 DAH. These results suggest that the utilization of newly absorbed N until a later period after heading is important for the achievement of high yields.     

Grain yield responses of lowland rice varieties to increased amount of nitrogen fertilizer under tropical highland conditions in central Kenya

Tropical highland conditions in Mwea Kenya, ensure the high radiation and the large day–night temperature differences. Such conditions are generally believed to promote rice growth and yield, but the current grain yield is lower than the expectation. In the current standard N fertilizer practice in Mwea, 75 kg nitrogen (N) ha^?1 is applied in three splits at fixed timing. The effects of increases in N fertilizer amount (125, 175, and 225 kg N ha^?1) on rice growth and yield were evaluated to test the hypothesis that unachieved high rice grain yield in Mwea is due to insufficient amount of N fertilizer. Two popular lowland varieties in Mwea (Basmati 370 and BW196) and two varieties reported as high yielding in other countries (Takanari and IR72) were used. Shoot dry weight (DW) increased with increases in the amount of N fertilizer applied in three splits at fixed timing, irrespective of variety. It reached approximately 20 t ha^?1 under increased N conditions (>75 kg N ha^?1) in several cases, indicating that high biomass production could be achieved by increasing N application rate. However, the increased biomass did not increase grain yield, due to decreased grain filling under high N conditions in all varieties. Thus, N amounts above 75 kg ha^?1 were ineffective for increasing grain yields in Mwea, where N fertilizer was applied in three splits at fixed timing. Increasing influence of low temperature under high N conditions may be one of the reasons for the decreased grain filling in Mwea.     

生态环境对籼粳交后代株型特性和产量构成的影响

 以两个籼粳稻杂交F2群体（F2 A：晚轮422/沈农265;F2 B：泸恢99/沈农265）为试材,在四川和辽宁同年种植,研究生态环境对株型特性、产量构成及其相互关系的影响。结果表明,生态环境对株型特性和产量构成因素具有较为明显的影响。从四川到辽宁,株高和穗弯曲度显著提高,而穗长、剑叶长、剑叶宽及剑叶张角则表现出降低趋势。在辽宁,有效穗数、千粒重、结实率以及产量均显著高于四川,每穗粒数则显著低于四川。千粒重、结实率和产量表现为Cw（长剑叶、弯穗）> Cz（长剑叶、直穗） > Dw（短剑叶、弯穗） > Dz（短剑叶、直穗）,穗数和每穗粒数以Dz最低,Cz和Cw较高。剑叶长与产量构成因素间的相关性均未达到显著水平,而剑叶宽与每穗粒数均呈显著或极显著正相关,在辽宁,剑叶宽与结实率呈显著负相关。穗弯曲度只在四川分别与结实率及产量显著或极显著正相关,在辽宁则表现为与大多数产量构成因素相关不显著。     

Characterizing N uptake and use efficiency in rice as influenced by environments

To compare N uptake and use efficiency of rice among different environments and quantify the contributions of indigenous soil and applied N to N uptake and use efficiency, field experiments were conducted in five sites in five provinces of China in 2012 and 2013. Four cultivars were grown under three N treatments in each site. Average total N uptake was 10–12 g m^?2 in Huaiji, Binyang, and Haikou, 20 g m^?2 in Changsha, and 23 g m^?2 in Xingyi. Rice crops took up 54.6–61.7% of total plant N from soil in Huaiji, Binyang, and Haikou, 64.3% in Changsha, and 63.5% in Xingyi. Partial factor productivity of applied N and recovery efficiency of applied N in Changsha were higher than in Huaiji, Binyang, and Haikou, but were lower than in Xingyi. Physiological efficiency of soil N and fertilizer N were lower in Changsha than in Huaiji, Binyang, and Haikou, while the difference in them between Changsha and Xingyi were small or inconsistent. Average grain yields were 6.5–7.5 t ha^?1 (medium yield) in Huaiji, Binyang, and Haikou, 9.0 t ha^?1 (high yield) in Changsha, and 12.0 t ha^?1 (super high yield) in Xingyi. Our results suggest that both indigenous soil and applied N were key factors for improving rice yield from medium to high level, while a further improvement to super high yield indigenous soil N was more important than fertilizer N, and a simultaneous increasing grain yield and N use efficiency can be achieved using SPAD-based practice in rice production.     

氮肥运筹对水稻产量及氮素利用率的影响

以北方超级稻沈农265为材料,研究了氮肥运筹对水稻产量形成及氮素利用率的影响.结果表明:施纯氮210kg/hm2,且基蘖肥与穗粒肥比为6∶4时,由于单位面积有效穗数较其他处理提高2.4％～21.1％,致使产量提高3.3％～20.2％;同一基蘖肥与穗粒肥施用比例下,随施氮量的增加,沈农265的总吸氮量呈上升趋势,而氮素利用率有下降趋势;不同施氮量条件下,穗粒肥比例增加有利于总吸氮量和氮素利用率的提高;适宜施氮量和基蘖肥与穗粒肥比例,能为水稻整个生育期提供比较平衡的氮素供应,提高氮肥利用效率,协调产量构成因素,从而提高产量,节本增效.     

不同密度杂草稻对栽培稻群体形态特征及产量的影响

在沈农265田中插入不同密度的杂草稻WR03-12,研究杂草稻对栽培稻生产的影响。结果表明:杂草稻的竞争对栽培稻的叶片长宽和株高影响不大,对栽培稻的产量影响较大,在9、7、5、3、1株杂草稻/m2处理中,栽培稻分别减产44.65%、36.89%、24.67%、17.58%、1.37%,其中使栽培稻显著减产的最低密度为3株杂草稻/m2。杂草稻的竞争使栽培稻的穗数和穗粒数显著减少,结实率和千粒重略有降低。     

Yield potential and water use efficiency of aerobic rice (Oryza sativa L.) in Japan

Intensive rice farming in aerobic soil, referred to herein as aerobic rice, can greatly reduce the water input compared to that of flooded rice cultivation. The objective of this study was to compare the potential productivity of aerobic rice and flooded rice using high-yielding varieties at two locations in Japan in two successive years. In aerobic fields, the total amount of water supplied (irrigation plus rainfall) was 800–1300 mm. The soil water potential at 20-cm depth averaged between −15 and −30 kPa each growing season, but frequently reached −60 kPa. The average yield under aerobic conditions was similar to or even higher than that achieved with flooded conditions (7.9 t ha⁻¹ in 2007 and 9.4 t ha⁻¹ in 2008 for aerobic versus 8.2 t ha⁻¹ for flooded). The average water productivity under aerobic conditions was 0.8–1.0 kg grain m⁻³ water, slightly higher than common values in the literature. The super-high-yielding cultivar Takanari achieved yields greater than 10 t ha⁻¹ with no yield penalty under aerobic conditions in 3 out of 4 experiments. The favorable agronomic characteristic of Takanari was its ample sink capacity (grain number × grain weight). In conclusion, high-productivity rice cultivation in aerobic soil is a promising technology for water conservation. With continued breeding, future aerobic rice varieties will possess large numbers of spikelets and sufficient adaptation to aerobic conditions such that they will consistently achieve yields comparable to the potential yield of flooded rice.     

Identification of quantitative trait loci for panicle structure and grain filling using a cross between indica- and japonica-type high-yielding rice cultivars

ABSTRACT

To enhance the yield potential of rice by breeding, it is important to reveal the genetic factors affecting yield components in high-yielding cultivars. Quantitative trait loci (QTL) analysis for panicle structure and spikelet weight as an index of grain filling was conducted using recombinant inbred lines (RILs) derived from a cross between an indica-dominant high-yielding cultivar, Takanari, and a japonica-dominant high-yielding cultivar, Momiroman in 2012 and 2013 in eastern Japan. The grain-filling ability of Takanari is reported to be better than that of Momiroman. Since grain filling is generally better near the tip of the panicle and decreases as the number of branches from the rachis increases, we classified whole panicles into upper and lower side panicles and spikelets into primary, secondary, and tertiary spikelets according to the number of branches from the rachis. On chromosomes 1, 4, and 6, QTLs regulating the number of spikelets per panicle and panicle structure were detected and were most likely identical to GN1a, SPIKE, and APO1, respectively, which has been previously reported as QTLs regulating the number of spikelets per panicle. Takanari produced much heavier secondary and tertiary spikelets than Momiroman on the lower side panicle. On chromosome 5, novel QTLs regulating spikelet weight were detected. The Takanari allele enhanced secondary and tertiary spikelet weight on the lower side panicle. These results indicate that it may be possible to enhance sink capacity and translocation of source with a combination of novel QTLs detected on chromosome 5 and GN1, APO1, and SPIKE.     

两种穗型粳稻穗内粒间直链淀粉含量变异与粒位分布特征

以6个直穗型和4个弯穗型粳稻品种为材料,对两者在相同栽培条件下的穗内粒间直链淀粉含量变异及其频数分布、粒位特征进行了比较分析。结果表明：水稻穗型虽然与品种间的直链淀粉含量高低无直接关系,但对其穗内不同籽粒间的直链淀粉含量差异存在着较大的影响;直穗型粳稻品种单一稻穗内直链淀粉含量的粒间差异明显大于弯穗型品种,其直链淀粉含量的粒间变异系数与离散程度均高于后者;同一稻穗内不同籽粒间的直链淀粉含量变化与其相应的粒位有关,两种穗型粳稻品种均表现为穗顶部籽粒的直链淀粉含量相对较高、穗基部籽粒的直链淀粉含量相对较低这一基本趋势。但与弯穗型粳稻品种相比,直穗型粳稻品种大量低直链淀粉含量籽粒产生的部位是在其稻穗的中部,而不仅仅局限在稻穗基部的3个枝梗上。     

寒地直立穗型与弯曲穗型水稻干物质生产与转运研究

对直立穗型与弯曲穗型水稻不同生育时期干物质生产转运进行对比分析。结果表明,两种穗型水稻苗期充实度差异达显著水平,直立穗型高于弯曲穗型;营养生长期直立穗型干物质积累有高于弯曲穗型水稻的趋势;两种穗型水稻茎鞘输出率截然相反,弯曲穗型输出而直立穗型却有积累;两种穗型水稻抽穗后的干物质积累对产量的贡献率都大于85%,直立穗型水稻后期贡献大于弯曲穗型,且均超过90%;直立穗型水稻抽穗前干物质转运率低于弯曲穗型。     

氮肥不同施肥方法对超高产水稻品种“沈农265”生理特性的影响

进行了氮肥不同施肥方法对超高产水稻品种"沈农265"主要生理性状的研究。试验结果表明:"沈农265"最佳施肥方法为施肥法A;CGR、NAR均与叶片叶绿素含量呈正相关;SLW与叶片含氮量呈显著正相关;在5个主要生育期叶氮、叶碳、叶绿素含量的最适值均与产量存在回归关系。     

氮素穗肥运筹对两个杂交中籼稻叶片形态、光合生产及产量的影响

【目的】为探究氮素穗肥不同促花肥和保花肥比例对水稻光合生产和产量的影响,并为水稻氮素穗肥管理提供依据,【方法】以株型和产量均存在较大差异的2个杂交中稻品种(德香4103和宜香3724)为材料,在常规施氮量(180 kg/hm2)下,研究了占总氮40%的穗肥不同促花肥和保花肥运筹比例(1∶3,2∶2,3∶1,4∶0)对水稻叶片生长、形态、光合生产及产量的影响。【结果】2个水稻品种均在低促花肥、高保花肥时(1∶3)表现出叶片直立、受光形态好,净光合速率高和群体干物质积累量大的特点,并最终获得较高产量;而在高促花肥、低保花肥下,2个水稻品种的剑叶、倒2叶叶面积和叶角增大,披垂度增加,群体质量变差,结实率和粒重下降,产量降低。德香4103因其颖花量较大,上3叶叶面积和总叶面积相对适宜,粒叶比高,且在不同穗肥运筹下叶面积和叶角变幅较小,因而受光姿态和群体质量更优,干物质积累量更大,产量更高。【结论】水稻氮素穗肥运筹应塑造良好叶片形态和群体质量,并增加花后物质积累量才能有助于产量提高;并对水稻株叶型选育进行了探讨。     

超高产粳稻品种抗倒伏性的初步研究

以沈阳农业大学水稻研究所培育的超高产粳稻品种为材料,研究了超高产粳稻品种的抗倒伏能力及与倒伏密切相关的各性状指标。结果表明:齐穗后30 d左右是水稻最容易发生倒伏的时期,株高与水稻倒伏指数呈极显著正相关,茎秆基部伸长节间性状与倒伏关系密切,茎秆维管束数目、厚壁细胞层数、淀粉和可溶性糖含量均对倒伏有一定影响。超高产粳稻品种沈农265和沈农9741与常规粳稻品种辽粳294和辽粳371相比,表现出较好的抗倒性能。     

硅肥对北方粳稻产量和品质的影响

 以沈农265和丰优2000为材料,在盆栽条件下,研究了硅肥不同施用量对水稻产量和品质的影响。结果表明,施用硅肥能提高水稻产量,其中有效硅240 kg/hm2使沈农265显著增产,有效硅180 kg/hm2对丰优2000增产效果达到显著水平。从产量构成因素上看,施用硅肥能提高每穴穗数、一次枝梗上籽粒千粒重、二次枝梗上籽粒千粒重、每穗粒数。施用硅肥能显著改善稻米品质,主要表现为稻米的糙米率、精米率和整精米率显著提高,稻米的垩白粒率和垩白度显著降低。相关分析表明,两品种的精米率和整精米率与有效硅施用量呈正相关。沈农265的稻米脂肪酸含量与有效硅施用量呈正相关,食味值与有效硅施用量呈负相关。有效硅施量在0~240 kg/hm2内,两品种直链淀粉含量和蛋白质含量与有效硅施用量相关不显著。综合考虑各处理稻米产量和品质,以180~240 kg/hm2的有效硅施用量较好。     

减氮后中日粳稻品种杂交后代株型、产量和米质的变化及其相互关系

【目的】研究氮肥减施后中日粳稻品种杂交构建的重组自交系(RIL)群体株型、产量和米质性状的变化规律及其相互关系。【方法】以中国东北地区典型的直立穗型水稻辽粳5号与日本的优质米水稻秋田小町（弯曲穗型）杂交构建的RIL群体为试材,在高氮和低氮两种施肥模式下,调查株型、产量及米质性状,分析三者间的关系,探讨高产、稳产、高食味值类型株系的共同特征。【结果】氮肥减施后RIL群体齐穗期提前,株高降低,剑叶、倒2叶、倒3叶叶片变窄变短,剑叶基角变小,倒3叶基角变大,结实率、千粒重、经济系数增大,单株穗数减少,产量下降,糙米率和精米率提高,食味值提高。在两种施肥模式下,高产高食味值类型株系与低产低食味类型株系的显著区别是植株较高,叶片长,穗子长,一次枝梗结实率高,着粒密度较小;高产稳产类型株系的共同特征是剑叶较窄、剑叶基角较大;高产稳产高食味值类型株系的共同特征是剑叶和倒2叶较窄。【结论】株型特征可以用来间接选择高产、稳产、高食味值的水稻品种。