Maize kernel growth and kernel water relations as affected by nitrogen supply

Improving maize (Zea mays L.) growing conditions near flowering by applying nitrogen (N) could affect both kernel number per unit area (KN) and potential kernel weight (KW). Potential kernel weight can be estimated with maximum kernel water content (MKWC), as final kernel weight and kernel water relations are strongly associated in maize. At the crop level, the product of KN per unit area and MKWC could provide an appropriate index of potential sink capacity. The main objective of this study was to determine if the decrease in potential sink capacity (i.e. the product of MKWC and KN), under N deficit and with a late planting date, is due to MKWC or KN reductions. Additionally, we evaluated sink growth rate per unit area (i.e. the product of KN and kernel growth rate) during grain fill period as related to potential sink capacity. Three N rates under optimal and late planting dates and two hybrids were evaluated in experiments carried out at Paraná, Argentina (31°50′S; 60°31′W) during 2002–2003 and 2003–2004 growing seasons (seasons 1 and 2, respectively). Except for the late planting date during season 1, there was a significant positive response on grain yield, KN, KW, and MKWC to N supply. Experiments explored a broad range of KN, from 1645 to 5066 kernel m⁻². MKWC and KN were positively correlated for DK682. Nitrogen increased the potential sink capacity and sink growth rate only as KN increases from a particular threshold in both hybrids. The sink growth rate was largely related to potential sink capacity, as MKWC was highly correlated with KGR across all treatments. Our analytical approach, considering potential sink capacity as a product of KN and MKWC, is integrative of sink demand both for individual kernel and crop levels. This work highlights the role of early establishment of potential sink capacity on yield determination under a wide range of N conditions.     

Source–sink relations and kernel weight differences in maize temperate hybrids

Maize (Zea mays L.) kernel weight (KW) response to changes in assimilate availability per kernel during grain filling suggests that plants establish an early kernel sink potential that place them to grow close to a saturating assimilate availability condition during late grain-filling, meaning source limitations are common only early in kernel development. As maize reproductive efficiency in kernel set is not constant across different plant growth rates (PGR) around flowering, we used PGR per kernel during this period as an indicator of source availability per kernel. We tested whether PGR per kernel during flowering or during the effective grain-filling period were correlated to genotypic and environmental differences in final KW. Plant growth rate during both periods, KW, kernel growth rate during the effective grain-filling period, total duration of grain filling and kernel number per plant were measured in 12 commercial genotypes differing in KW sown at two sites under full irrigation. As expected from the curvilinear response relating kernel number per plant and PGR around flowering, increased PGRs resulted in higher PGR per kernel around this period (r² = 0.86; p < 0.001). Differences in final KW due to genotypes or environments were significantly explained by the PGR per kernel around flowering (r² = 0.40; p < 0.001), and not by the PGR per kernel during the effective grain-filling period. Genotypes differed in kernel growth rate (p < 0.001) and grain-filling duration (p < 0.001). The former was well explained by PGR per kernel around flowering (r² = 0.66; p < 0.001), but showed no relationship with the PGR per kernel during the effective grain-filling period. Grain-filling duration was partially explained (r² = 0.27; p < 0.01) by the ratio between PGR per kernel during the effective grain-filling period and kernel growth rate, but differences in duration were negligible compared to those observed in the ratio (∼41% versus ∼130%, respectively). Together, these results support the importance of source availability per kernel during early grain filling on the determination of maize potential sink capacity and final KW. Early resource availability per kernel was accurately estimated as PGR per kernel around the period of kernel number determination, which helped explain genotypic and environmental differences in maize final KW as well as in kernel growth rate.     

Source/sink ratio and the relationship between maximum water content,maximum volume,and final dry weight of maize kernels

Final kernel weight (KW) is closely related to maximum kernel volume (KV) and maximum kernel water content (KWC). It is not clear, however, how changes in the reproductive sink capacity, assimilate availability during grain filling and physical restriction to kernel expansion affect the relationship between KW and KWC or between KW and KV. Three experiments were conducted at Balcarce, Argentina and Ames, USA. Defoliation, thinning, plant density, restricted pollination and volume restriction treatments were imposed to manipulate KV, sink and source capacity. KW varied from 111 to 436 mg across all hybrid–treatments combinations and was related to the source/sink ratio during grain filling (r² = 0.85). Treatment variation in KW was related primarily to changes in kernel growth rate, except for the complete defoliated treatment, which also shortened the duration of grain filling. KW was correlated with maximum KWC (r² = 0.77, p < 0.001) and with maximum KV (r² = 0.91, p < 0.001). The developmental patterns for KW, KWC and KV during grain filling were not affected by the source/sink manipulations, except for severe defoliation. In the latter case, maximum KWC was not a good estimate of final KW. KV, however, was sensitive to reductions in carbohydrate supply during grain filling and was closely correlated to KW. Physical restriction to kernel expansion reduced kernel weight 13% relative to its control (p < 0.01). But restricting kernel expansion did not alter the general relationships between KW and KWC or between KW and KV, because kernel density was not affected.     

Predicting maize kernel sink capacity early in development

Development of maize (Zea mays L.) kernels follows a predictable pattern involving rapid increase in dry weight and large changes in water content (WC). We showed previously that final kernel weight (KW) was closely correlated with maximum WC achieved during rapid grain filling. The objectives of the current work were (i) to test if percent moisture content (MC, measured on a fresh weight basis) could be used to normalize genetic and environmental variations in kernel development shown to affect final KW and (ii) to determine whether final KW could be predicted from kernel WC prior to rapid grain filling. The data examined included results from five hybrids varying more than 2-fold in final KW grown in the field, and from previously published results. When KW and WC were expressed relative to their maximum values obtained during kernel development, a single model described the relationship between dry weight accumulation and MC for the larger seeded hybrids (199–352 mg kernel⁻¹) and published results (222–359 mg kernel⁻¹). Two smaller seeded yellow-flint popcorn hybrids, however, accumulated less dry matter per unit moisture than expected. Nonetheless, all genotypes exhibited a common developmental relationship between kernel WC (expressed as a percent of the maximum value) and MC under well-watered conditions. A new model was developed to couple this developmental relationship to final KW. This model accurately predicted final KW from kernel WC values measured prior to rapid grain filling (∼80% MC; root mean square error, RMSE, of 28.9 mg kernel⁻¹) for all hybrids examined and all published results for which KW and kernel WC data were available. The model also provided a simple means to determine whether final KW was limited by photosynthate supply during kernel development.     

Plasticity of sorghum kernel weight to increased assimilate availability

Understanding source or sink limitations on crop yield is critical for the rational design of agricultural practices as well as breeding strategies. In the present article, we studied sorghum [Sorghum bicolor (L.) Moench] source–sink yield limitations during grain filling, and tested the hypothesis that the time in which kernel maximum water content is reached during grain filling defines a temporal limit for the crop to profit from source increases. Earlier studies have never tested increasing assimilate availability per kernel in different developmental stages. We conducted a field experiment increasing assimilate availability per kernel at anthesis and 15 days after anthesis in commercial hybrids. The anthesis treatment was aimed to increase assimilates per kernel from early grain filling, and the 15 days after anthesis treatment from the stage kernel maximum water content was achieved. Both treatments removed 50% of the kernels from one side of the panicle. Kernel dry weight (KW), kernel water content and kernel volume were measured in apical and basal positions of the panicle throughout grain filling. Increased assimilate availability always yielded a higher KW (34% increase). This KW increase was consistent across the two kernel developmental stages when the treatment was imposed, the panicle position and hybrid. Achieving maximum water content did not prevent kernels from increasing their weight when assimilates were subsequently increased. Final KW was closely related to maximum kernel volume (r² = 0.72; n = 42; p < 0.0001). Increased assimilate availability per kernel promoted changes in both kernel growth rate and duration of grain filling.

We applied a quantitative approach for determining the magnitude of sorghum KW changes in response to assimilate availability changes during grain filling. This allowed us to compare our data to previously published articles, and to determine any general response pattern across environments. The analysis supported our observation that sorghum KW is highly responsive to increased assimilates, and indicated that increased assimilate availability during filling always increased sorghum KW. As such, growth of sorghum kernels is predominately source limited; breeding and management practices aimed to increase assimilate availability per kernel will be likely to enhance sorghum yield. Results show that the crop has the capacity to profit from source increases even after the initial grain-filling stages have occurred.     

两种供氮水平下玉米穗部性状的QTL定位

以优良杂交种豫玉22两亲本Z3和87-1为基础构建一套F8家系的重组自交系群体为研究材料,在正常供氮和低氮两种氮水平下进行田间试验,利用复合区间作图法对玉米穗长、穗行数、行粒数、百粒重和单穗粒数进行QTL定位分析。两种氮水平下共定位到24个玉米穗部性状的QTL位点,其中正常供氮条件下定位到13个QTL,低氮水平下定位到11个QTL,集中分布在第1(8个QTL)、第5(6个QTL)和第8(5个QTL)染色体上。两种氮水平下共位或紧密连锁的QTL位点较少,表明玉米穗部性状在低氮水平下的遗传机制发生很大改变。研究发现,第1染色体umc1122/bnlg1556位点是一个控制低氮水平下玉米单穗粒数的主效QTL,单个QTL可解释19.7%的表型变异,该位点还同时影响低氮水平下玉米穗长、穗行数和百粒重的表型。与前人定位结果比较发现,该位点所在的染色体区域是一个产量及氮效率相关性状的QTL富集区,对此位点附近进行相关分子标记辅助选择,可能会在玉米氮高效分子育种上有所突破。     

Grain yield components in maize: II. Postsilking growth and kernel weight

Maize kernel weight (KW) results from kernel growth during two stages of grain filling, the lag phase (formative period) and the effective grain-filling phase. Environmental conditions may affect kernel biomass accumulation in each phase. This work analyzed: (1) changes in duration and rate of kernel growth on a thermal time (°C day) basis; and (2) KW response to postsilking biomass production kernel⁻¹ (source:sink ratio). Sowing date, plant population, and nitrogen fertilization experiments were conducted in France and Argentina to induce changes in assimilate availability per kernel. Hybrids of different KW were tested. Hybrids differed in the duration of the lag phase, which determined kernel growth rate during the effective grain-filling period for hybrids with similar grain-filling duration (ca. 745°C day). Environments with low air temperature (<19°C) and less incident solar radiation led to a smaller final KW due to reductions in photoassimilate production and its partition to the grains. A value of 240 to 270 mg kernel⁻¹ during grain filling was determined as a threshold to have mobilization or storage of reserves. Small-kernel hybrids (KW<300 mg), with large kernel number (3500 to 5500 kernels m⁻²), depended more on reserve mobilization than large-kernel hybrids (KW>300 mg) with reduced kernel number (2800 to 4000 kernels m⁻²). For the former, grain yield increments should not be based on increased kernel number but on increased biomass production.     

Crop management affects dry-milling quality of flint maize kernels

Dry-milling performance of maize (Zea mays, L.) kernels primarily depends on their hardness. The flint type is harder than the dent and semi-dent maize, yielding a higher proportion of big endosperm pieces in the mill. Nevertheless, crop growing conditions could modify milling properties. The objective of this work was to analyze the effect of different crop environments and management practices on dry-milling quality of flint maize kernels. Two orange-flint hybrids from different eras of breeding differing in flint type expression and grain yield potential were evaluated. They were grown at three different locations of the Argentina's main maize-production area under different sowing dates, plant densities, and fertilization rates during two growing seasons. Crop post-silking growth, grain yield and its components (kernel number and weight), kernel size and hardness-associated properties (test weight, percent floaters and milling ratio), and flaking-grit yield were analyzed. Most of observed differences in physical properties of kernels, particularly for the high-yielding new hybrid with unstable flint expression, were associated with the source-sink ratio established during the post-silking period (explored range from 154 to 617 mg kernel⁻¹). This variable mainly results from changes in crop growth during that period. Increases in weight per kernel improved hardness-associated properties. High crop grain yields together with top dry-milling quality were achieved when the new high-yielding hybrid was cropped with an appropriated crop management.     

Enhanced kernel set promoted by synchronous pollination determines a tradeoff between kernel number and kernel weight in temperate maize hybrids

Maize (Zea mays L.) grain yield is strongly related to the number of harvested kernels, where kernel number can be increased by synchronously pollinating silks rather than allowing them to be progressively pollinated as they naturally appear from the husks. However, there is scarce evidence on how this practice affects kernel weight (KW) and plant grain yield (PGY), and no report exists on its effects when combined with treatments aimed to reduce apical dominance, like male sterility and detasseling. Field experiments were conducted in two growing seasons (Exp₁ and Exp₂) using two hybrids, cropped at contrasting stand densities (3 and 9 plants per m²) and including (i) male-fertile and male-sterile versions, (ii) tasseled and detasseled plants, and (iii) natural (NP) and synchronous pollination (SP; pollen added manually to ears bagged 5 days after initial silking) systems. Tassel growth of sterile and fertile versions was also evaluated in a separate experiment (Exp₃). Detasseling increased the number of ears per plant reaching silking (P < 0.001) of NP plants, but this beneficial effect of reduced apical dominance did not improve kernel number per plant (KNP) or PGY. Similarly, the early arrest of anther growth in male-sterile plants had no clear benefit on KNP. In contrast, KNP was enhanced by synchronous pollination (range between −13% and +71%; average of +15.4% in Exp₁ and +3.9% in Exp₂). However, this pollination system promoted a decreased in KW (range between −30% and +4%; average of −11.8% in Exp₁ and −7.8 in Exp₂) such that the treatment had no effect on PGY (range between −19% and +37%; average of +1% in Exp₁ and −4% in Exp₂). Because plant growth rate around flowering was not different between pollination treatments, assimilate availability per kernel was reduced from ovary fertilization onwards in synchronously pollinated plants when compared to open pollinated plants. This explains the reduced KW when increasing KNP by synchronous pollination. In summary, none of the imposed treatments allowed grain yield to be increased at the plant level.     

不同基因型玉米氮素吸收利用效率研究进展

玉米氮效率的评价方法与指标不尽一致,导致对玉米基因型不同的分类结果。玉米氮效率研究主要集中于根系对氮素的吸收、叶片对氮素的还原同化、氮素在植株体内的积累和分配以及地上部生长势与氮效率的关系方面。以子粒为主要收获对象的玉米,穗、子粒发育状况对玉米产量起着关键作用,有关穗、子粒发育对玉米氮效率贡献率的大小、不同氮效率基因型玉米穗、子粒发育的差异以及内在生理生化机制研究较少。对不同氮效率基因型玉米子粒发育与氮效率之间关系、子粒发育尤其是顶部子粒的早期发育(决定穗粒数的形成)对氮素的反应、氮高效品种顶部子粒的早期发育是否优于氮低效型、氮素对不同氮效率基因型玉米子粒发育的影响机制等问题有待进一步研究。     

Kernel water relations and duration of grain filling in maize temperate hybrids

Kernel water relations play a key role in controlling the duration of grain filling. This duration is controlled by the relationship between kernel water and biomass development, as it determines the timing kernels reach a critical percent moisture content (MC, measured on a fresh weight basis) at which biomass accumulation stops. The time in which this critical percent MC is attained can be affected by the timing kernel net water uptake stops (i.e. maximum water content is reached), or by the relationship between water loss and biomass deposition after maximum water content is attained. Which of the two mechanisms could be behind genotypic differences in maize (Zea mays L.) grain-filling duration was unknown. We also studied the relationship between kernel water and volume development, as it was unknown in this species. Thirteen commercial hybrids were evaluated under different growing environments, and weight, water content and volume of their kernels were measured throughout grain filling.     

不同生产方式下的玉米产量构成影响因素分析

试验对不同生产方式下的玉米产量构成影响因素进行对比分析,制定"玉米田养鹅"模式下的玉米增产策略。结果表明,玉米田养鹅处理(RGC-E)玉米行粒数、穗粒重和产量显著低于对照(P0.05),RGC-E处理穗粒重与百粒重的相关系数比对照CK低0.453,穗粒重与穗行数的相关系数比CK高0.279,"玉米田养鹅"处理对穗粒重与穗行数、百粒重之间的相关关系产生明显影响。CK处理的百粒重通过行粒数对产量的正向间接作用最大,间接通径系数为0.475,RGC-E处理的穗行数通过行粒数对产量的正向间接作用最大,间接通径系数为0.301。因此,RGCE处理下的玉米产量构成因子的作用发生变化,在继续提高行粒数的基础上,通过提高玉米穗行数的遗传力来增加玉米产量。     

利用乙烯利塑造夏玉米凹形冠层对产量及其相关性状的影响

以紧凑型玉米品种浚单20为试验材料,通过拔节期不同的乙烯利喷施处理塑造不同的冠层结构,考察其对生长发育及产量性状的影响。结果表明:隔带(以2行为一带)喷施乙烯利的处理(间喷处理)可以形成凹形冠层,在高密度条件下,凹形冠层比全矮冠层(全层喷施乙烯利,全喷处理)及常规冠层(全层喷水处理,对照)表现出明显的增产效果,间喷处理增加了群体内边行优势并改善了群体下层受光状态。研究认为,通过人为措施(如隔带化控和高矮品种带状间作)塑造凹形群体结构是进一步提高玉米群体生产力的重要途径。     

遮光对不同基因型玉米叶片衰老和产量的影响

采用盆栽试验,研究了遮光对不同基因型玉米叶片衰老和产量的影响。结果表明,苗期遮光和穗期遮光均使玉米叶面积指数L(AI)降低,但粒期遮光则使玉米生育后期LAI下降减缓。遮光条件下生长的玉米叶片SOD酶活性升高,MDA含量降低。不同时期遮光处理均可导致玉米减产,减产程度为粒遮>穗遮>苗遮。除千粒重和穗粗外,遮光处理对其它穗部性状指标的效应值均达极显著水平。遮光对玉米叶片衰老和产量的效应在不同基因型之间表现出明显差异。     

Diallel cross analysis in durum wheat (Triticum durum Desf.): identification of best parents for some kernel physical features

A complete diallel cross study of three local populations (Ahmet, Dallı and Iri) and one cultivar (Çakmak-79) of durum wheat (Triticum durum Desf.) was carried out with parents and F₁ progeny, to determine heterotic patterns, correlations, heritability and combining ability of various kernel physical features. The relative importance of additive vs. non-additive genetic effects was also determined. The general combining ability (GCA) and specific combining ability (SCA) components of variance were significant for all of the features examined, but reciprocal effects (RE) were significant only for kernel projected area (KPA) and kernel rupture strength (KRS). GCA effects were dominant for kernel length (KL), KPA, kernel sphericity (KS) and thousand kernel weight (TKW). The magnitude of GCA variance was more pronounced than SCA variance for all these features. However, SCA effects were dominant for kernel width (KW), kernel height (KH) and KRS. KRS, an important parameter during sowing, harvest and milling, had significantly positive linear correlations with KL, KH, KPA and TKW and negative correlations with KS. TKW in durum wheat can be increased by selecting progenies with high KL, KH and KPA values whereas the opposite is true with higher KW and KS values. Accordingly, the parent Iri used in this study appears to be a suitable donor in breeding programs where improved kernel physical features are desired. Path and stepwise regression analyses revealed that KH has been the major feature in increasing TKW due to its high direct effect on this feature. On the other hand, KW and KS were the main features directly contributing to higher KRS values. It is suggested that early selection of breeding lines with respect to higher KH and to higher KW and KS should help breeders to improve cultivars with better KRS and TKW values, respectively.     

氮肥运筹对郑单1002和郑单958冠层特征和产量的影响

以郑单1002和郑单958为材料,0(N0)、150(N1)、300(N2)kg/hm2氮肥水平,常规尿素和一次性基施掺混控释肥两种氮肥类型,研究不同氮肥运筹对夏玉米冠层特征、干物质积累与分配和产量的影响。结果表明,增加施氮量,两个品种穗位层和近地表叶面积指数(LAI)比N0处理增加25.7%~52.5%,开花期和成熟期干物质积累、千粒重、穗粒数、穗长和产量显著增加,农学利用效率降低22.0%~40.0%。与常规尿素相比,掺混控释肥增加玉米生长后期穗位层和近地表的透光率和成熟期干物质积累,提高了千粒重、穗粒数、产量和氮肥农学效率,降低子粒含水率。在相同施肥条件下,与郑单958相比,郑单1002的LAI和穗粒数分别提高7.5%~14.8%和2.3%~11.5%,千粒重降低1.4%~6.2%,产量提高0.8%~6.2%。     

The effect of nitrogenous fertiliser application on leaf traits in durum wheat in relation to grain yield and development

Nitrogen (N) fertilisation boosts the grain yield of wheat through its influence on yield components, phenology and leaf traits. Both crop growth and senescence are dependent on N supply, as are the number of kernels set per unit area and per ear, and the mean kernel size. A two-season trial of four semi-dwarf durum wheat cultivars, grown at two levels of N, was used to illustrate the effects of N on canopy temperature, leaf resistance and flag leaf senescence pattern under irrigated conditions in a Mediterranean climate, and to explore the consequences of these effects on the crop phenology, its yield and its yield components. The well-fertilised crop developed a larger leaf area index at anthesis and a lower leaf resistance, thus generating a lower canopy temperature and delayed anthesis. Its grain fill duration was shorter, in spite of its lower canopy temperature, presumably because the increased N availability resulted in the development of a stronger sink (more kernels per unit area and per ear), which was associated with earlier senescence, thereby shortening the duration of grain fill, and led to reduced kernel weight.     

南方丘陵红壤旱地不同施肥模式对春玉米生物学特性及产量的影响

以当地常规施肥模式(CK)为对照,研究南方丘陵红壤旱地不同施肥模式(CO:常规施肥+有机肥;CB,常规施肥+生物有机肥;CP:常规施肥+钾肥)对春玉米生物学特性及产量的影响。结果表明,单株叶面积和叶面积指数大小顺序为CO>CP>CB>CK处理,全生育期单株叶面积和叶面积指数均显著高于对照,抽雄期和成熟期CO和CP处理均显著高于其他处理。拔节期、抽雄期和成熟期CO和CP处理植株根系干重、茎干重均显著高于其他处理,CO处理植株叶干重显著高于对照。CO处理穗长显著高于对照;CP处理行粒数、穗粒数和百粒重均显著高于对照。CO、CB和CP处理产量分别比对照增加19.36%、13.08%和22.10%,增产原因主要是行粒数、穗粒数和百粒重的增加。     

播期与密度对玉米物质生产及产量形成的影响

以郑单958为试验材料,研究播期与密度对玉米物质生产及产量形成的影响。结果表明,播期与密度和玉米群体干物质积累关系紧密,早播密植、晚播稀植有利于群体干物质积累;随播期推迟,产量呈下降趋势,且播期越晚,产量下降越显著。产量构成因素对产量的贡献率因气象条件而异,穗数和千粒重对产量贡献率较大,且随播期推迟均有所降低;花前充足的光辐射、花期适量的降水及花后适宜的有效积温对玉米产量有明显促进作用。苗后50~60 d的光辐射对穗数影响极显著,光辐射及降雨量与穗粒数也呈显著正相关;苗后70 d至成熟期的有效积温对千粒重影响显著。因此,适当调节播期,使玉米生长发育的关键时期处于最适的气象条件有利于发挥玉米高产潜力。     

深松与播期对玉米冠层结构及产量性状的影响

通过深松和播期对玉米冠层结构的调控,分析深松与旋耕条件下不同播期群体冠层结构特点,明确塑造高产群体冠层结构的耕作方式及适宜播期。采用裂区设计,主区耕法设2个水平(深松与旋耕),副区播期设3个水平(4月25日、5月10日和5月25日),研究深松与不同播期对玉米冠层结构及产量性状的影响。结果表明,深松可适当延长玉米生育进程,对玉米植株形态、叶面积指数(LAI)、群体光合势(LAD)、干物质积累特征参数及产量的影响均表现为深松>旋耕(CK);播期处理间其冠层结构、产量及产量构成因素存在显著差异,表现为早播>中播>晚播;随着播期推迟,早播(4月25日)产量较5月10日、5月25日分别提高3.61%和43.38%。说明深松条件下早播利于群体形成合理的冠层结构,可有效提高玉米产量。