Determination of grain number in sorghum

Grain number is an important component of grain yield in sorghum. Research in wheat and maize has indicated a dependency of grain number on the crop or panicle growth rate around anthesis (CGR_a and PGR_a respectively), but little quantitative information is available for sorghum. The aim of this paper was firstly to quantify the effect of CGR_a and PGR_a on grain number and secondly, to identify other parameters that could be used as substitutes for PGR_a. Analyses included data from a number of experiments, covering a range in nitrogen and drought treatments and including both tall (single dwarf) and short (triple dwarf) hybrids. CGR_a and SGR_a (stem growth rate) were calculated from the derivative of a curvilinear function fitted to experimental data, and PGR_a was obtained by subtraction of SGR_a from CGR_a. Results indicated a linear relationship between grain number and CGR_a, but the slope differed for tall and short hybrids. This was due to a difference in the proportion of dry matter allocated to the reproductive organs around anthesis (P_r), as PGR_a was closely related to grain number, irrespective of crop height. Since panicle dry mass at maturity (excluding grain) was closely correlated with reproductive biomass shortly after anthesis, this indicator represents an integration of panicle growth during the critical period for yield determination in sorghum (i.e. flag leaf until start of grain filling). Panicle biomass at maturity (excluding grain) was thus also linearly related to grain number, and the relationship was independent of crop height and of the timing, severity, or type of stress. Our results indicate that panicle mass at maturity could provide an alternative to PGR_a for the estimation of grain number.     

Characterization of sorghum genotypes for traits related to drought tolerance

Grain sorghum (Sorghum bicolor L. Moench) is a genetically diverse cereal crop grown in many semiarid regions of the world. Improving drought tolerance in sorghum is of prime importance. An association panel of about 300 sorghum genotypes from different races, representative of sorghum globally, was assembled for genetic studies. The objectives of this research were to (i) quantify the performance of the association panel under field conditions in Kansas, (ii) characterize the association panel for phenological, physiological and yield traits that might be associated with tolerance to limited moisture (drought), and (iii) identify genotypes with higher yield potential and stability under different environments that may be used in the sorghum breeding program. Results show large diversity for physiological and yield traits such as chlorophyll content, leaf temperature, grain numbers and grain weight per panicle, harvest index and yield. Significant differences were found for plant height, grain weight and numbers per panicle, harvest index, and grain yield among and within races. The US elite lines had the highest number of grains and grain weight per panicle while the guinea and bicolor races recorded the lowest. Harvest index and yield was highest for the US elite lines and the caudatum genotypes. Overall, there was a negative correlation between plant height and grain weight, grain numbers and yield. Harvest index and grain numbers were negatively affected by moisture limitation for all the races. Among the races, the caudatum genotypes were more stable in grain yield across the different environments. Overall, there was a wide variability within the association panel for physiological and yield traits that may prove to be useful for improving drought tolerance in sorghum.     

Identification of deletion mutants with improved performance under water-limited environments in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a semi-aquatic member of the grass family that is poorly adapted to dry environments and has greater sensitivity to water-deficits than other important cereals in this family. To increase productivity in aerobic or water-limited environments rice must overcome its adaptations to flooded environments. Deletion mutants offer an alternative genetic resource for improving drought tolerance. Almost 3500 IR64 deletion mutants were screened under vegetative and reproductive stage drought stress in the field and evaluated for leaf drying and/or grain yield. Seven novel conditional mutants of rice which showed gain of function through continued growth as drought stress developed compared to the wild type were identified. Mutant recovery rate was 0.1%. Further evaluation of putative drought mutants revealed that their average shoot biomass at maturity and grain yield per plant under stress exceeded those of the wild type by two-fold. Studies under controlled conditions confirmed mutants to have continued growth of both roots and shoots as drought developed compared to the wild type, and a tendency for greater water extraction. We propose that deletions in these mutants have affected a regulator of the highly conservative growth response common to irrigated lowland rice cultivars. Our results suggest that screening deletion mutants for performance under managed drought stress in the field could be a highly effective way to identify valuable genetic resources for improved drought response and aerobic adaptation in rice.     

Growth and development in tall and dwarf isogenic lines of spring wheat

The objective of the experiments reported here was to analyse the nature of the effects of the Rht dwarfing genes on yield potential in spring wheats, using near-isogenic lines of Yaqui 50 and Ciano 67 grown controlled environments. Although tall and dwarf lines had similar relative growth rates at all stages, the taller plants were consistently larger throughout due to faster and more uniform germination. Stem weight at anthesis-whether total or residual-was reduced by the Rht genes in proportion to height. Leaf length and area were much less affected by the Rht genes than was stem length, and later-formed leaves of dwarf plants could even be larger than in their tall counterparts at cool temperatures. Peak photosynthetic rates were similar in talls and dwarfs, the small differences usually reflecting differences in leaf size or specific leaf weight. Root weight was initially heavier in the taller lines, but after the stage of rapid stem elongation it tended to be heavier in the dwarfs. Tillering could be greater or less in the dwarfs depending on environmental conditions, stage, and genotype.Inflorescence initiation was somewhat earlier in the dwarf lines and their inflorescences were therefore initially heavier, and remained so up to anthesis under low irradiance and warm temperatures. But under high irradiance and/or cool temperatures, after an initially slower start the inflorescences of the taller lines eventually became the heavier. Ear weight at anthesis was closely correlated with grain number per ear at maturity and with grain yield per ear in Yaqui 50, but less closely in Ciano 67 lines, in which grain set was reduced at lower temperature when additional Rht genes were present. No evidence was found for a specific effect of the Rht genes in raising grain number. Ear weight at anthesis was relatively less affected than stem weight by adverse conditions, especially in the shorter lines. Nevertheless, across all conditions there was a close relation between stem and ear weights at anthesis, which differed between lines of different height but which closely fitted one regression when ear weight was related to the weight per unit length of stem. Under low irradiance and high temperature the greater stem growth of the taller lines was associated with smaller ears, but at high irradiance and cool temperatures both ears and stems were heavier in the taller lines.Treatments with GA₃ or CCC, to which only the tall lines responded, showed that ear weight at anthesis did not vary with large increase or decreases in stem weight, but grain set and kernel weight could be changed substantially.The yield-determining effects of the Rht genes thus varied with stage of development and environmental conditions, and with genetic background, which may have to be adjusted in order to optimise the effects of the Rht genes on yield potential, suggesting that comparisons of isogenic lines may not always provide a satisfactory indication of the potential value of major genes in breeding programs.     

种植密度对不同穗型冬小麦品种结实特性和产量的影响

为了明确种植密度对冬小麦结实特性和产量的影响，于2020-2021年以大穗型品种衡观35和多穗型品种济麦22为试验材料，设置4个种植密度水平，分别为每公顷基本苗180万（D180）、300万（D300）、420万（D420）和540万（D540）株，比较分析了不同种植密度下冬小麦小花结实、籽粒空间分布特征和产量的差异。结果表明，随着种植密度的降低，衡观35主茎穗上部和I分蘖穗下部、济麦22主茎和I分蘖穗中上部小穗位的结实粒数呈增加的趋势。降低种植密度促进了两个品种穗中部小穗位弱势小花、上部和下部小穗位强势小花的结实。衡观35主茎穗中上部和I分蘖穗中部小穗位的结实粒数均高于济麦22。开花期穗干重与可孕小花数呈显著正相关。低种植密度处理下开花期穗干重的增加为其获得较高的穗粒数奠定了良好的物质基础。种植密度对千粒重影响不显著，但显著降低了衡观35的穗数。由于产量构成三要素的协调作用，两个品种均在D300处理下获得了最高产量，但与其余种植密度处理间差异均不显著。综合来看，在保证穗数的前提下，适当降低种植密度会促进冬小麦主茎和分蘖穗结实，进而增加穗粒数和产量，可节约生产成本，有利于冬小麦绿色高产高效生产。     

Plant characteristics associated with weed competitiveness of rice under upland and lowland conditions in West Africa

Weeds are a major constraint to rice (Oryza spp.) production in West Africa. Superior weed competitive rice genotypes may reduce weed pressure and improve rice productivity. Two upland and two lowland experiments were conducted in southern Benin to examine genotypic variations in weed-suppressive ability and grain yield under weedy conditions, and to identify plant characteristics that could be used as selection criteria for improved weed competitiveness. A total of 19 genotypes, including Oryza sativa and Oryza glaberrima genotypes and interspecific hybrids developed from crossing O. sativa and O. glaberrima, were grown under weed-free and weedy conditions in an upland with supplemental irrigation and in a flooded lowland. In weedy plots, hand weeding was done once or not at all. Mean relative yield loss across all genotypes due to weed competition ranged from almost 0% to 61%. Large genotypic variations in weed biomass and grain yield under weedy conditions were found. Visual growth vigor at 42 and 63 days after sowing (DAS) under weed-free conditions significantly correlated with weed biomass at maturity in both upland and lowland experiments (R² = 0.26–0.48). Where weed pressure was low to moderate, with mean relative yield loss less than 23%, the multiple regression models using grain yield and plant height at maturity or only grain yield measured under weed-free conditions as independent variables could explain 66–88% of the genotypic variation in grain yield under weedy conditions. At higher weed pressure (mean relative yield loss: 61%), as observed in one of the upland experiments, biomass accumulation of rice at 42 days after sowing was associated with higher grain yield under weedy conditions. Biomass accumulation also significantly correlated with visual growth vigor at the same sampling dates. Therefore, we conclude that grain yield, plant height at maturity and visual growth vigor at 42–63 DAS under weed-free conditions appear to be useful selection criteria for developing superior weed competitive rice genotypes.     

Comparative toxicity of selected insecticides to pea plants and growth promotion in response to insecticide-tolerant and plant growth promoting Rhizobium leguminosarum

Laboratory and field/pot experiments were conducted to determine the effect of two insecticides, fipronil and pyriproxyfen, on growth, symbiotic properties (nodulation and leghaemoglobin content), amount of N and P nutrients in plant organs, seed yield and seed protein of pea plants. In addition, the role of the most promising fipronil and pyriproxyfen tolerant Rhizobium leguminosarum strain MRP1 having plant growth promoting traits such as, production of phytohormones and siderophores, was also assessed in the presence and absence of both insecticides. Generally, fipronil and pyriproxyfen at the tested rates (recommended and higher doses) decreased the growth of both R. leguminosarum inoculated or uninoculated pea plants. Of the various concentrations of the two insecticides, pyriproxyfen at all concentrations in general, showed comparatively more severe toxicity to pea plants by decreasing plant biomass, symbiotic attributes, nutrients (nitrogen and phosphorus) uptake, seed yield and grain protein over the uninoculated control. The sole application of 3900 μg pyriproxyfen kg⁻¹ soil (three times the recommended dose) showed the highest toxicity and decreased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 20%, 27%, 25%, 29%, 15% and 2% respectively, compared to the control. Interestingly, when the inoculant strain MRP1 was used with any concentration of the two insecticides, it significantly (P ≤ 0.05) increased the measured variables (plant dry weight, nodule numbers, dry nodule biomass, leghaemoglobin, nitrogen and phosphorus uptake, seed yield and grain protein) when compared to the plants grown in sandy clay loam soils treated solely (without inoculant) with the same individual treatment of each insecticide. For instance, three times the recommended dose of pyriproxyfen with strain MRP1 showed a highest stimulatory effect and increased the root nitrogen, shoot nitrogen, root phosphorus, shoot phosphorus, seed yield and grain protein by 108%, 124%, 119%, 153%, 112% and 6% respectively, compared to the plants grown in soil treated solely with three times the recommended dose of pyriproxyfen.     

Evaluation of CIMMYT conventional and synthetic spring wheat germplasm in rainfed sub-tropical environments. II. Grain yield components and physiological traits

CIMMYT hexaploid spring wheat (Triticum aestivum L.) germplasm has played a global role in assisting wheat improvement. This study evaluated four classes of CIMMYT germplasm (encompassing a total of 273 lines), along with 15 Australian cultivars (Oz lines) for grain yield, yield components and physiological traits in up to 27 environments in Australia's north-eastern region, where terminal drought frequently reduces grain yield and grain size.Broadly-adapted CIMMYT germplasm selected for grain yield had greater yield potential and improved performance under drought stress, being up to 5% greater yielding in High-yielding (mean yield 429 g m⁻²) and 4-10% greater yielding than adapted Oz lines in Low-yielding environments (mean yield 185 g m⁻²). Whilst maintaining statistically similar harvest index and spikes m⁻² compared to broadly-adapted Oz lines across all environments, sets of selected CIMMYT lines had greater canopy temperature depression (0.18-0.27 °C), dry weight stem⁻¹ (0.20-0.37 g), increased grains spike⁻¹ (0.8-3.4 grains), grain number m⁻² (ca. 20-800 grains), and maturity biomass (56-83 g m⁻²). Compared to selected Oz lines, broadly-adapted CIMMYT lines had a smaller reduction in Low compared to High-yielding environments for these traits, especially dry weight stem⁻¹, such that CIMMYT lines had ca. 25% and 10% greater dry weight stem⁻¹ than the Oz lines in Low- and High-yielding environment groups, respectively. Broadly-adapted CIMMYT germplasm also had slightly higher stem water soluble carbohydrate concentration at anthesis (ca. 6 mg g⁻¹), which contributed to their higher grain weight (ca. 0.5 mg grain⁻¹), and maintained an agronomically appropriate time to anthesis and plant height. Thus current CIMMYT germplasm should be useful donor sources of traits to enrich breeding programs targeting variable production environments where there is a high probability of water deficit during grain filling. However, as multiple traits were important, efficient introgression of these traits in breeding programs will be complex.     

大麦株高近等基因系的磷素利用效率特性分析

为明确大麦株高对磷素利用效率的影响,采用土培盆栽试验,以4对两种遗传背景下的大麦株高近等基因系为材料,设置施磷(P_2O_5:60 mg·kg~(-1)土)和不施磷两种磷处理,于成熟期采样,分析其农艺性状、磷含量、磷素利用效率等差异。结果表明,施磷处理下大麦近等基因系株高、单株产量、单株秸秆干重及收获指数均较不施磷处理增高,高秆大麦的株高、穗长、芒长、产量及收获指数均显著大于矮秆大麦,而其单株秸秆干重小于矮秆大麦。施磷处理下近等基因系根系、秸秆、籽粒磷含量及磷积累量整体高于不施磷处理。不施磷处理下,高秆大麦的秸秆磷含量及磷积累量整体小于矮秆大麦,而其籽粒磷积累量整体大于矮秆大麦,最大高出矮秆大麦89.87%。施磷处理下大麦的根系、秸秆及籽粒磷素利用效率小于不施磷处理,秸秆磷素利用效率变化最大,施磷为不施磷的25%～68%,其中高秆大麦变化幅度大于矮秆大麦。经相关性分析,大麦单株产量与籽粒磷积累量呈显著正相关,与根系磷积累量呈极显著或显著负相关;穗长与秸秆磷利用效率、株高与磷收获指数以及芒长与磷收获指数在施磷和不施磷处理下分别呈显著负相关和正相关。相较于矮秆大麦,高秆大麦在低磷环境下具有更高的收获指数及磷收获指数,说明高秆大麦具有更高的耐低磷特性。因此,在缺磷土壤中选择株高较高的大麦能获得更好的经济效益。     

Ecophysiological determinants of biomass and grain yield of wheat under P deficiency

Grain yield of crops can be expressed as a function of the intercepted radiation, the radiation use efficiency and the partitioning of above-ground biomass to grain yield (harvest index). When a wheat crop is grown under P deficiency the grain yield is reduced but it is not clear how these three components are affected. Our aim was (i) to identify which of these components were affected in spring bread wheat under P deficiency at field conditions and (ii) to relate the grain yield responses to processes of grain yield formation during the spike growth period. Three field experiments were conducted in the potentially high wheat yielding environment of southern Chile. All experiments had two levels of P availability: with (155 kg P ha⁻¹) or without P fertilization (average soil P-Olsen concentration of 10 ppm, a medium level of P availability). High wheat grain yields were obtained varying between 815 and 1222 g m⁻² with P applications. Experiments showed a grain yield reduction caused by P deficiencies of 35, 16 and 18% in experiments 1, 2 and 3, respectively. This was related (R² = 0.99, P < 0.01) to a reduction in the total above-ground biomass at harvest and not to the harvest index. Reductions in above-ground biomass were due to a reduction in radiation intercepted under P deficiency without effecting radiation use efficiency. Grain number per square meter was the main yield component (R² = 0.99, P < 0.01) that explained the grain yield reduction caused by the P deficiency which was due to low spike biomass at anthesis (R² = 0.96, P < 0.05). The reduction in spike biomass at anthesis was related (R² = 0.86, P < 0.01) to reductions in crop growth rate during the spike growth period as a consequence of a lower radiation intercepted during this period. This study showed that under high wheat yield conditions the main effect of a P deficiency on grain yield reduction was a negative impact on the total above-ground biomass due to the negative impact on intercepted radiation, particularly during the spike growth period, affecting negatively spike biomass at anthesis and consequently grain number and yield.     

Agronomic assessment of Bt trait and seed or soil-applied insecticides on the control of corn rootworm and yield

Corn rootworm (Diabrotica spp.) has become the most concern and widespread insect pest of corn (Zea mays L.) production in North America. Two field experiments were conducted to assess the agronomic and yield performance of transgenic rootworm trait, Bacillus thuringiensis (Bt) Cry3Bb, seed-coating treatment, and a soil-applied insecticide under natural corn rootworm infestation. Experiment 1 compared a conventional corn hybrid with and without insecticide (Force 3G) with its near isoline Bt hybrid from 2003 to 2005, on a clay loam soil. Experiment 2 investigated the same treatments as in Experiment 1 plus an additional seed-coated Poncho treatment on a sandy loam in 2004 and 2005. Rootworm population before the crop anthesis, root node injury and root:shoot dry weight ratio during the early grain filling stage, and stalk lodging and grain yield were determined. Our data showed that rootworm population diminished over the 3 years owing to rootworm displacement and adverse weather conditions. At the clay loam site, both Force 3G and the Bt hybrid significantly reduced the larval populations, root injury and lodging score, and increased root:shoot ratio. Over the 3 years, grain yields of the Bt hybrid were 11–66% greater than the untreated non-Bt isoline hybrid; yield of the non-Bt hybrid treated with Force 3G was also significantly greater than the same untreated non-Bt hybrid in 2 of 3 years. Despite less root node injury in the first rows of non-Bt plants adjacent to the Bt plots was observed, yield benefit of this effect remained to be proven. On sandy loam soil, the larval population was very low and there were no differences in root node injury and plant lodging among all the four treatments in either 2004 or 2005. The yield of the Bt hybrid was up to 10% greater than its non-Bt isoline hybrid treated or not with an insecticide in 1 year. Our data showed that Bt rootworm seed technology was effective to control the rootworm larvae and protected grain yield under severe infestation. Furthermore, our data suggest that some of the gain in Bt hybrid yield may be attributed to the genetic transformation as observed in sandy loam soil experiment. In all cases, corn producers should be aware of the pest history, rootworm pressure in relation to economic threshold, soil type and the expected cost-to-benefit ratio before deciding to adopt any protective measures.     

Functional dynamics of the nitrogen balance of sorghum: I. N demand of vegetative plant parts

Stay-green, an important trait for grain yield of sorghum grown under water limitation, has been associated with a high leaf nitrogen content at the start of grain filling. This study quantifies the N demand of leaves and stems and explores effects of N stress on the N balance of vegetative plant parts of three sorghum hybrids differing in potential crop height. The hybrids were grown under well-watered conditions at three levels of N supply. Vertical profiles of biomass and N% of leaves and stems, together with leaf size and number, and specific leaf nitrogen (SLN), were measured at regular intervals. The hybrids had similar minimum but different critical and maximum SLN, associated with differences in leaf size and N partitioning, the latter associated with differences in plant height. N demand of expanding new leaves was represented by critical SLN, and structural stem N demand by minimum stem N%. The fraction of N partitioned to leaf blades increased under N stress. A framework for N dynamics of leaves and stems is developed that captures effects of N stress and genotype on N partitioning and on critical and maximum SLN.     

Use of uniconazole to control plant height for an industrial/pharmaceutical maize platform

A variety of crops and their production systems have been proposed as platforms for plant-made pharmaceuticals (PMPs) and plant-made industrial compounds (PMICs), each with their own advantages and challenges. Maize grown in isolated, confined environments avoids several challenging issues associated with future production of PMPs/PMICs. When grown under optimizing conditions of temperature, nutrition, and water status, however, maize tends to elongate excessively, which contributes to lodging and interferes with delivery of sufficient overhead electric lighting to the inner foliar canopy where ears develop. Suppression of extensive stem elongation without compromising grain yield would help in delivering overhead light into the foliar canopy for efficient grain production. The plant-growth retardant uniconazole (UCZ) was tested for its effects on maize height and grain yield. UCZ reduced plant height effectively, but dosages that strongly suppressed stem elongation also decreased grain yield, ear length, and cob weight. Duration of growth suppression was prolonged at high UCZ concentrations. UCZ also induced branching of maize, which was enhanced as concentrations increased. A range of ear types occurred on branches, with some conversion of ears to tassels at high UCZ concentrations. Minimum stem diameter declined with increasing UCZ concentration. Plant height was reduced from 306 cm to 232 cm (−25%) using a concentration of 1.0 mg/L UCZ without affecting grain yield of 180-200 g per plant. This low UCZ concentration caused 1-2 basal branches to form that would not affect planting density in a cropping situation.     

6-BA对小麦开花期渍害的缓减效应

为了解6-苄氨基嘌呤(BA)对小麦开花期渍害的减缓效应,在大田条件下,于2012-2013和2013-2014年度,以郑麦9023为材料,研究了开花期喷施BA对小麦光合、干物积累及产量的影响。结果表明,开花期渍水使小麦两年分别减产51.4%和52.3%,减产的主要原因是千粒重和穗粒数降低,尤其是千粒重的下降,而穗粒数的减少主要归因于弱势粒的减少(两年分别减少21.4%和71.4%)。渍水前喷施6-BA处理比渍水处理显著增产,两年分别增产7.8%和31.6%,增产的主要原因是提高了千粒重和穗粒数。渍水前喷施6-BA可提高旗叶光合速率及SPAD值、干物质积累总量及收获指数,缓减旗叶及倒三叶衰老。说明渍水前喷施6-BA可通过促进小麦光合作用和干物质积累及其向籽粒的分配,减缓渍水对产量形成的不利影响。     

叶面喷施亚硒酸钠对黑粒小麦籽粒硒含量、产量及品质的影响

为了明确亚硒酸钠对黑粒小麦籽粒硒含量、产量及品质的影响,以黑粒小麦品种山农紫麦1号为材料,在大田进行叶面喷施亚硒酸钠,亚硒酸钠设4个浓度:0(CK)、15(C_1)、30(C_2)和45(C_3)g·hm~(-2),分别于小麦拔节和开花期各喷施一次,分析了不同浓度亚硒酸钠黑粒小麦花后叶面积指数、干物质积累与分配、产量、籽粒硒含量及品质性状。结果表明,开花后各时期的叶面积指数(LAI),C_1、C_2处理均显著高于CK,C_3处理在开花后14～21d显著高于CK;成熟期植株干物质重及籽粒、茎秆+叶鞘、穗轴+颖壳的干物质重,C_1、C_2处理均显著高于CK,但叶片干物质重及占比显著低于CK;花后干物质积累量,C_2、C_3处理显著高于CK,C_1处理与CK无显著差异。三种喷亚硒酸钠处理(C_1、C_2和C_3)的成穗数均显著高于CK,而穗粒数和千粒重差异不显著,产量较CK分别增加7.89%、9.96%和9.19%。叶面喷施亚硒酸钠显著提高黑粒小麦籽粒的硒含量,CK、C_1、C_2和C_3处理籽粒硒含量分别为0.056、0.238、1.295和1.207mg·kg-1。籽粒粗蛋白含量,C_1、C_2处理较CK分别提高9.49%和4.29%,差异显著;C_1、C_2、C_3处理面筋指数分别较CK提高4.67%、13.06%和3.77%;C_1处理面团形成时间及稳定时间均显著高于CK,C_2、C_3处理与CK差异不显著;各喷施亚硒酸钠处理间的湿面筋含量、沉淀指数和吸水量差异不显著。本研究条件下,黑粒小麦拔节期和开花期各喷施30mg·kg-1亚硒酸钠,可以明显提高籽粒产量、硒含量与品质。     

花后弱光对江汉平原稻茬小麦的产量及碳、氮分配效应的影响

为了探究连阴雨天气弱光逆境导致小麦减产的机理,于2017-2018年度对长江中下游流域适宜推广的48个小麦品种开展了灌浆期全程遮光试验（遮去自然光强的45%）,初步筛选出两个弱光敏感品种（扶麦1228和生选6号）和两个弱光钝感品种（襄麦55和扬麦158）,2018-2019年以此4个品种和江汉平原主推品种郑麦9023为供试材料,研究了开花期至成熟期遮光对小麦干物质积累与分配、植株氮素转运及籽粒产量的影响。结果表明：（1）花后遮光后小麦籽粒产量显著降低,两年度5个品种平均减产49.1%～61.1%,千粒重平均下降34.4%～42.5%,遮光对穗数和穗粒数的影响两年度均未达0.05显著水平。（2）花后遮光抑制了小麦干物质的积累,显著减少各营养器官干物质积累量,使成熟期干物质积累总量较CK平均下降23.4%,降低籽粒灌浆速率。花后遮光增大了营养器官花前同化物的转运量及其对籽粒产量的贡献率,而减少了花后光合同化物量及其贡献率,降低收获指数。（3）花后遮光后营养器官中氮素向籽粒的再分配受抑,较多的氮素滞留在营养器官中,茎鞘氮素积累量平均增加了88.0%,穗轴与颖壳次之,叶片增加了32.8%。遮光导致各营养器官花前贮存氮素向籽粒的转运量和转运效率均显著下降,使籽粒氮素积累对花后吸收氮素的依赖加大。总之,花后遮光会导致小麦显著减产,其主要原因是粒重大幅度下降;遮光加大了籽粒干物质积累对花前碳水化合物再分配的依赖,以及籽粒氮素积累对花后氮素吸收的依赖。襄麦55和扬麦158遮光条件下籽粒产量下降幅度较小,是稻麦周年高产适宜推广品种。     

Physiological and Agronomic Consequences of Rht Genes in Wheat

Summary

Yield of wheat has risen dramatically and world-wide in the last two decades, in part because of the widespread introduction of Rht genes that reduce the length of tillers of wheat. We review the physiological consequences of incorporating reduced height genes into wheat. The Rht₁ or Rht₂ genes modulate the morphology and physiology of wheat in a manner that involves compensation among several physiological processes. For instance, Rht genes decrease leaf area, but photosynthesis per unit area increases, so biomass accumulation is rarely altered. Although Rht genes increase leaf permeability to water vapor, plant water status changes in compensation to minimize differences in water use efficiency. Perhaps due to less competition for carbohydrate during stem elongation, semidwarf wheat has greater harvest index than tall wheat at maturity. Although tall wheat has a greater weight per kernel at maturity, this does not completely compensate for greater grain number per spike in semidwarf wheat. The compensation that leads to greater yield in semidwarf wheat appears to fail in Rht₁Rht₂ or Rht₃ dwarf wheat. Either specific photosynthesis does not completely compensate for decreased area per leaf, or the reduction in plant height retards canopy closure and efficient interception of solar radiation, resulting in lower biomass and yield of dwarf wheat. Drought stress reduces yield and harvest index of dwarf wheat more than tall wheat. Rht genes have insignificant effects on rate of development or winter hardiness. The effects of Rht genes on physiology appear to be similar in winter, spring and durum wheat.     

Evaluation of the yield potential and physicochemical properties of the biomass of Salix viminalis × Populus tremula hybrids

This study presents the characteristics of four Salix viminalis × Populus tremula hybrids, produced for the first time in the world grown in a three-year field experiment. Shoot weight per plant and major biomass yield components, including plant height, number of shoots per rootstock and shoot diameter, were determined. The infection severity caused by leaf rust (Melampsora sp.) was also evaluated. The biomass of three-year-old hybrid plants was subjected to chemical analyses and calorimetric tests to determine the energy value of biomass as solid fuel. Among the studied genotypes the highest yield was achieved by one of the studied hybrids. Its biometric parameters did not differ significantly from the standard genotype, and they were superior to the parameters of the maternal form. All Salix × Populus hybrids were more susceptible to rust infections than their maternal form and one hybrid was more resistant to infections caused by fungi of the genus Melampsora. Two hybrids have optimal biomass parameters as regards both calorific value and amount of carbon, hydrogen, sulfur and nitrogen.     

冀东地区种植密度对小麦京冬8号抗倒伏能力和产量的影响

为明确冀东地区种植密度对冬小麦抗倒伏能力和产量的影响,于2011-2013年度以当地推广的冬小麦品种京冬8号为材料,设每公顷375万、525万、675万和825万株4个种植密度处理,分析了不同密度下小麦茎秆质量、抗倒伏指数和产量的差异.结果表明,密度增大使小麦基部第1节间增长,增加了基部节间长在茎长中所占的比例、株高和重心高度,导致茎秆变细,茎秆机械强度和抗倒伏指数降低.当密度达到每公顷675万株时,小麦出现倒伏,密度再增加,倒伏时间提前,倒伏程度增大.群体干物质积累量在生育前期随密度增加而增加,但大密度导致植株分蘖衰亡较多,降低生育后期干物质生产能力,至成熟时以每公顷525万株的干物质积累量和花前营养器官贮存干物质向籽粒的运转量最多.虽然每公顷675万株的有效穗数最多,但由于倒伏严重,其千粒重最轻,每公顷825万株的有效穗数和穗粒数均较少,因此这两个高密度处理的产量均较低.综合来看,在冀东地区,适期播种条件下,小麦京冬8号以种植密度为每公顷375万～525万株为宜,此密度下茎秆质量较高,抗倒伏能力较强,产量较高.     

Genotypic variation in linear rate of grain growth and contribution of stem reserves to grain yield in wheat

Grain growth in wheat depends on current photosynthesis and stem water-soluble carbohydrates (WSC). In semiarid regions with terminal drought, grain filling in wheat crops may depend more on stem WSC content than on current assimilates. Reduction in grain yield under drought is attributed to shorter duration of linear grain growth despite increased contribution of stem reserves to grain yield. The amount of stem reserves is measured either by changes in stem dry weight (indirect method) or by stem WSC content (direct method). Genotypic variation in the rate and duration of linear grain growth and in percent contribution of stem reserves to grain yield has not been evaluated in wheat. The objectives of this study were: (i) to quantify the relationship between the direct and indirect measurement of stem reserves during and across the grain-filling period and (ii) to measure the extent of genotypic variation in rate and duration of linear grain growth and in percent contribution of stem reserves to grain yield. Dry weight, WSC content and grain yield of the main stem were measured at 10-day intervals in 11 diverse wheat genotypes under well-watered and droughted-field conditions across 2 years. Drought reduced stem WSC content from 413 to 281 mg and grain yield from 4.6 to 2.5 t ha⁻¹. Stem WSC content and dry weight were positively correlated. Genotypic differences in linear rate of grain growth were significant in well-watered (ranging from 48.9 to 72.4 mg spike⁻¹ day⁻¹) and in droughted-field (ranging from 33.2 to 59.9 mg spike⁻¹ day⁻¹) conditions. Drought, on average, reduced the linear rate and duration of grain growth by 20 and 50%, respectively. Reduction in linear rate ranged from 13 to 43%. The amount of current assimilates and stem reserves contributed to grain yield was reduced, respectively, by 54 and 11% under drought. Genotypic differences in percent contribution of stem reserves to grain yield were significant in well-watered (ranging from 19.1 to 53.6%) and in droughted-field (ranging from 36.6 to 65.4%) conditions. The wheat genotypes responded differently to drought. Main spike grain yield was reduced by 43% under drought due to 26 and 11% reduction in grain weight and number of grains, respectively. Grain yield was correlated with linear grain growth under well-watered (r = 0.96) and droughted (r = 0.83) conditions. The genotypic variation observed indicates that breeding for a higher rate of linear grain growth and greater contribution of stem reserves to grain yield should be possible in wheat to stabilize grain yield in stressful environments.