Spikelet Positions Research Articles

Image facilitated assessment of intra-spike variation in grain size in wheat under high temperature and drought stress

In wheat (Triticum aestivum L.), the grain size varies according to position within the spike. Exposure to drought and high temperature stress during grain development in wheat reduces grain size, and this reduction also varies across the length of the spike. We developed the phenomics approach involving image-based tools to assess the intra-spike variation in grain size. The grains were arranged corresponding to the spikelet position and the camera of smart phone was used to acquire 333 images. The open-source software ImageJ was used to analyze features of each grain and the image-derived parameters were used to calculate intra-spike variation as standard deviation (ISVAD). The effect of genotype and environment were highly significant on the ISVAD of grain area. Sunstar and Raj 4079 contrasted in the ISVAD of grain area under late sown environment, and RNA sequencing of the spike was done at 25 days after anthesis. The genes for carbohydrate transport and stress response were upregulated in Sunstar as compared to Raj 4079, suggesting that these play a role in intra-spike assimilate distribution. The phenomics method developed may be useful for grain phenotyping and identifying germplasm with low intra-spike variation in grain size for their further validation as parental material in breeding.

Seed position in spikelet as a contributing factor to the success of the winter annual invasive grass Aegilops tauschii.

Seed position – dependent effects on seed dormancy/germination are well documented at the inflorescence/infructescence level, but less is known about seeds at different positions within a dispersal unit. For the invasive winter annual grass Aegilops tauschii, we quantified morphology, mass and dormancy/germination of seeds from basal (1), middle (2), and distal (3) positions in two spikelet types (Left and Right). We also investigated seedling emergence, survival, plant size and seed production of plants from seeds in different spikelet positions of two spikelet types under different soil nutrient and water conditions. We found that these seed, seedling and plant traits performed as mirror images between the Left and Right spikelet types. The middle seed was significantly the longest and had the maximum mass, while the basal seed was the shortest and had medium mass. Middle seeds had the highest increase in mass during imbibition and the highest germination percentages and rates, while basal seeds had the lowest. Seedling emergence and survival, plant size and seed production for each position of seeds were highest in the added fertilizer combined with regular watering treatment and lowest in the no fertilizer combined with natural moisture, while height of plants derived from the middle and the distal seeds was significantly higher than that of plants derived from the basal seeds under all soil nutrient and water conditions. Seedling survival, number of tillers per plant and seed production per plant from the middle and distal seeds were significantly lower than those from basal seeds under all soil nutrient and water treatments. The considerable variation in seedling emergence and survival, plant size and seed production between seeds in different positions in the spikelet results in much flexibility in all stages of the life cycle, thereby likely contributing to the invasiveness of A. tauschii.

Variation of floret development and grain setting characteristics in winter wheat responses to delayed sowing.

Wheat floret development has been a focus of research due to a desire to improve spike fertility, which majorly influences grain yield. Sowing date plays a vital role on grain yield in wheat, and increase in the grain number per spike of winter wheat (Triticum aestivum L.) has been obtained by delayed sowing. During the 2014-2015 and 2015-2016 growing seasons, variation in these developmental patterns was explored involving two winter wheat cultivars (Jimai 22 and Tainong 18) and five sowing dates (24 September; 1, 8, 15 and 22 October). We noticed clear differences in the grain number per spikelet; delayed sowing had a greater impact on the number of fertile florets at anthesis than grain set. Significant differences in the developmental patterns of florets among spikelet positions corresponded to variations in the floret developmental rate, with faster floret development associated with higher floret fertility. Delayed sowing did not affect the grain number near the rachis, but significantly promoted grain set on distal florets. Increased spike dry weight (SDW) did not compensate for floret size or grain weight, mainly due to enhanced assimilate partitioning to florets. Delayed sowing significantly affects floret developmental dynamics, causing differences in winter wheat floret fertility. An increased SDW concomitant with improved intra-spike partitioning before anthesis contributes to increase the distal floret numbers per spike and then optimize winter wheat spike fertility. © 2022 Society of Chemical Industry.

DEP1 affects rice grain weight and quality at different spikelet positions

AbstractGrains at different positions on rice panicles differ greatly in weight and quality, but few studies have focused on the effect of dep1 that influences panicle morphology and grain number on grain weight and quality at different spikelet positions and under different backgrounds. To clarify this, we compared spikelet characteristics and grain quality in the superior spikelets (SS) and inferior spikelets (IS), as well as sink‐, source‐ and flow‐related traits between NIL‐dep1 (AKI‐dep1 and LG5‐dep1) and NIL‐DEP1 (AKI‐DEP1 and LG5‐DEP1) under the Akitakomachi (AKI) and Liaogeng5 (LG5) backgrounds. The grain weight and quality in SS did not significantly differ between NIL‐dep1 and NIL‐DEP1 under the two backgrounds. However, the effect of dep1 on grain weight and quality in IS varied with background. AKI‐dep1 significantly decreased the grain weight, processing quality, and eating and cooking quality in IS compared with AKI‐DEP1, possibly due to poor grain filling and the lack of an adequate source supply and vascular system to fully meet the increased sink size. With the exception of appearance quality, the grain weight and quality of IS of LG5‐dep1 were similar to LG5‐DEP1, mainly due to the enlarged vascular system and similar grain filling rate and source supply. We concluded that the varied effects of dep1 on grain weight and quality under the two backgrounds could be attributed to differences in grain filling and source−sink−flow relationships.

Shading decreases rice yield by impeding grain‐filling progress after heading

AbstractShading stress decreases both the yield and quality of rice (Oryza sativa L.), which has become a serious problem in rice production worldwide. However, the effect of shading stress on the grain‐filling progress of rice is not well understood. In this study, field experiments were conducted to investigate the effect of shading on the grain‐filling progress and grain yield of rice at Hanyuan and Wenjiang in Sichuan, China, between 2018 and 2019. The results showed that shading after heading significantly decreased the spikelet‐filling rate and grain weight, as well as the dry weight of grains panicle–1, 30 d after shading; these traits were closely related to the grain yield of rice. Hence, the grain yield decreased by 13.72–22.54% and 6.86–14.35% at Hanyuan and Wenjiang, respectively. However, the influence of shading stress on the spikelet‐filling rate, grain weight, and dry weight of grains panicle–1 30 d after shading differed according to spikelet positions. In general, these influences were greater on spikelets at the bottom and middle positions than on those at the top position. Furthermore, the effects of shading stress on rice differed across study sites; shading stress had a greater effect on grain weight at Hanyuan, but a greater effect on spikelet‐filling rate at Wenjiang. Therefore, it is critical to improve both spikelet‐filling rate and grain weight of spikelets at the bottom and middle positions to maintain the grain yield of rice under shading stress.

Endosperm enrichment and physicochemical properties of superior and inferior grain starch in super hybrid rice.

A significant asynchronous phenomenon exists in super hybrid rice because of the differences in spike and spikelet positions, which affect the accumulation and properties of starch. However, little is known about the endosperm enrichment and physicochemical properties of starch in superior and inferior grains in super hybrid rice. Rice YY2640 was selected as study material to investigate the enrichment and physicochemical properties of starch in superior and inferior grains in super rice using semi-thin sections, X-ray diffraction and related technologies. Superior grain filling was a continuous process, whereas inferior grain only started 8-10days after anthesis. The order of starch accumulation starts in the central endosperm, then in the endosperm of the proximal vascular bundle and finally in the aleurone layer. Compared with the inferior grains, the superior grains have a higher 1000-grain weight, apparent amylose content, total starch content, average starch granule size, relative crystallinity, solubility and a resonance peak ratio at 1022/995cm-1 , whereas the swelling power and ratio of the resonance peak at 1045/1022cm-1 were lower. The final degree of hydrolysis of HCl, AAG and PPA of the superior grains were significantly lower than those of the inferior grains. The findings indicate that the different physicochemical properties of starch were mainly related to the development order of superior and inferior grains and the spatial enrichment of starch.

Comparison of the chemical and textural properties of germ‐remaining soft rice grains from different spikelet positions

AbstractBackground and objectivesRice with very low amylose content tends to have a good taste, while germ‐remaining rice is nutritive because it retains nutrient‐rich embryos. We cultivated a batch of new germ‐remaining rice varieties with very low amylose content, and good nutrition and taste. We tested the differences in taste quality between superior and inferior grains.FindingsThe plumule ratio of superior grain was significantly higher than that of inferior grain. The elasticity of the surface layer and whole layer of superior grains was greatly reduced, whereas quality of balance (stickiness/hardness) and tackiness were increased. The proportion of apparent amylose content (AAC) and amylopectin long‐chain branching (Fb3) decreased, whereas the proportion of medium‐length branches (Fb1+2) increased significantly. Correlation analysis showed that small value of aspect ratio and low proportion Fb3, especially the former, can improve the quality of balance of rice. Moreover, plumule ratio showed a high correlation with grain shape and filling degree.ConclusionsTherefore, for the specially developed rice, plumule ratio and edibility can be improved by promoting grain plumpness and weight ratio of the embryo, especially the inferior grain.Significance and noveltyFor rice taste improving, the contribution of grain filling was greater than that of chemical changes in the endosperm composition, and breeders should pay attention to grain shape improvement and filling to improve the taste of rice.

Radiotracer and radiation application for rapid measurement of contribution of stem assimilates towards grain filling and for alleviating terminal heat stress in wheat

Contribution of stem photoassimilates towards grain filling may have significance under stress, since it may force the plant to initiate an early leaf senescence, thereby limiting the availability of flag leaf photosynthates for grain filling. Radiotracer feeding of 14C-sucrose to the internode by stem injection method at 20 days stage after anthesis and measurement of 14C activity in grains at 5 days after foliar application of potassium iodide, meant to inhibit current photosynthesis by inducing leaf senescence, showed a gradual decline in flag leaf chlorophyll but an increase in accumulation of 14C particularly in the basal spikelet grains. However, a reduction in grain filling at all the sink positions within the wheat ear was measured with hastened leaf senescence. On the other hand, abiotic stresses such as high temperature stress, is known to cause an abortion of the basal florets in wheat and induce an early flag leaf senescence. We have earlier shown that seed gamma irradiation, at 0.1 kGy causes an increase in grain mass at middle and basal spikelet positions. In this paper we report that the reduction in grain yield in response to terminal heat stress can be compensated by gamma irradiation, owing to better stem reserve mobilization into the basal and middle spikelet under condition of stress induced senescence.

Grain number determination in durum wheat as affected by drought stress: An analysis at spike and spikelet level

Yield studies show that increases in grain yield are always accompanied by an increase in grain number and, hence, further increases in yield potential may require additional improvements in grain number. The improvement of modern durum wheat was mainly based on the introduction of semidwarf genes. A 2‐year field drought stress experiment, concerning two different genotype groups (landraces vs modern cultivars), was carried out under a rainout shelter in order (a) to assess the effect of water deficit on floret dynamics and grain number determination, (b) to explore the relationship between plant water status with grain number per spike and its components (i.e., spikelets per spike, fertile florets per spikelet and grain set) and (c) to quantify the importance of several plant traits in determining the final number of grains per spike and fertile florets per spike when the main source of variation is water availability. Compared to control (well irrigated), grain number per spike was reduced, depending on year, genotype and water availability level, by 12.4–58.7% and this reduction was evident almost in all spikelet positions along the spike. Although there were some doubts in the past about the increased sensitivity of semidwarf cultivars to drought stress, they were not confirmed from our results. In most of the cases, the variation in plant water status (by means of water potential index [WPI]) during floret primordia phase (FPP) explained most of the variance in grain number per spike, fertile florets per spikelet, grain set and fertile spikelets per spike. In general, increasing water stress intensity decreased grain number per spike by an average rate of 13.5 and 9.4 grains per 0.2 MPa decrease in WPI, in modern cultivars and landraces, respectively. However, seasonal and genotypic effects were evident by modifying the slopes of the linear regressions between WPI and the studied plant traits. Commonality analysis revealed that the number of fertile florets per spikelet was the best predictor of grain number per spike, indicating that there is still much space for further improvement for this trait in landraces. However, this trait has been clearly improved in modern cultivars, especially at the basal and central spikelets. Although the number of spikelets per spike was the best unique predictor of the number of grains per spike in modern cultivars, grain set presented the highest total effect.

Shading stress increases chalkiness by postponing caryopsis development and disturbing starch characteristics of rice grains

Chalkiness, one of the key factors in determining the market price and quality of rice grains, is markedly influenced by the environment. This study aimed to investigate the effectiveness of shading on rice chalkiness by conducting a field experiment in Wenjiang, Sichuan, China, in 2013 and 2015. Rice cultivars IIyou 498 and Yixiangyou 2115 were selected and shaded during the grain filling period; this resulted in a 53% shading environment. The results showed that chalkiness, caryopsis and amyloplast development, amylose content, and amylopectin chain-length distribution of rice grains, were markedly affected by shading. Shading significantly increased chalky rice rate and chalkiness degree of rice grains at the bottom of the panicle, which contributed to the increase in chalkiness of the entire panicle. Shading had a greater influence on grains at the bottom spikelet positions than on those at the top and middle positions. More loosely packed amyloplasts with greater airspace and reduction in amylose content of grains at the bottom spikelet positions were possibly due to the significant delay in the development of caryopsis. Furthermore, except for the bottom spikelet positions of Yixiangyou 2115, a reduction in short-length chains coupled to an increase in long-length chains of amylopectin was noted under shading. Shading increased rice chalkiness primarily by postponing caryopsis development at the bottom spikelet positions and disturbing the starch characteristics of rice grains. Therefore, more attention needs to be focused on the grains positioned at the bottom of panicle.

Relationships among the chalkiness, kernel size and endosperm cell morphology of rice kernels at different spikelet positions within a panicle

ABSTRACTThe occurrence of chalky kernels in rice is causally related to kernel size and endosperm morphology. This study aimed to investigate the occurrence of chalky kernels by analyzing kernel size, and the number and area of endosperm cells. Spikelets were sampled from upper and middle primary branches and lower secondary branches in a panicle, and divided into four categories: upper, middle, and lower perfect (PF) kernels and lower milky-white (MW) kernels. On the lower secondary branches, there was a higher percentage of chalky kernels, with smaller kernel lengths, widths and thicknesses, than the kernels on the upper and middle primary branches. MW kernels were smaller in size than PF kernels even on the same lower secondary branches. Regardless of grain appearance quality traits, the total areas of endosperm cross sections in lower kernels were significantly smaller than in upper kernels owing to the decreased cell area, and there was a significant negative correlation between the number of cells and average cell area. When the numbers and the areas of cells were analyzed using angular 30° intervals from the line connecting the center point and the dorsal vascular bundle, the MW kernels had significantly less cells than PF kernels near the ventral side at 120–180°. Thus, the decrease in the number of cells near the ventral side was a main causal factor in the decrease in MW kernel widths compared with PF kernel widths, and this suggested that cell division in MW kernels was inhibited at the early grain-filling stage.

Grain number and grain filling of two-row malting barley in response to variation in post-anthesis radiation: Analysis by grain position on the ear and its implications for yield improvement and quality

Grain weight is reported to be a relatively well conserved characteristic across spring barley (Hordeum vulgare L.) crops that vary in grain number m−2. Understanding the mechanisms that promote stability in grain weight is important to ensure that efforts to increase grain number beyond current high levels successfully increase yield without compromising grain quality. The aims of this study were to establish 1) whether post-anthesis grain abortion contributes to the stability of grain weight by helping match grain numbers to post-anthesis assimilate supply and 2) whether variations in post-anthesis assimilation per unit grain number affect the heterogeneity of grain weight. Field experiments were conducted in a high-yield potential environment for spring barley in 2011 and 2012. Crops were either shaded post anthesis (a 59% reduction in radiation incident on the crop) to reduce net carbon assimilation or grown unshaded. Grain growth was measured at different spikelet locations on the ear and on different shoots (main shoot and tillers) of the same plant. Shading crops from 14 days after anthesis until harvest maturity reduced yield by 19–20%, mean grain weight (MGW) by 12–16% and harvest index by 5–6%, but did not significantly affect grain number in either year. The magnitudes of these effects were considerably lower than the reduction in radiation imposed by shading suggesting some compensatory adjustment in radiation use efficiency or dry matter partitioning to grain after shading. The rate of grain filling was higher for grains in central spikelets than grains at distal or basal locations on the ear. Shading reduced the rate of grain filling to a similar extent (23–27%) at most locations evaluated on the ear, but had no effect on the duration of grain filling. In spite of the comparable effects of shading on grain growth across different spikelet positions and hierarchy of shoots, crops harvested after shading tended to have a more variable individual grain weight (larger interquartile range and coefficient of variation) than crops that were unshaded. The results show that post-anthesis grain abortion does not contribute to the stability of MGW in spring barley. Moreover, low levels of post-anthesis radiation in crops of large grain number m−2 (sink capacity) can increase heterogeneity of grain weight, which may have negative consequences for grain quality.

飼料用米水稲新品種候補「岩手122号」の収量構成要素および穂の着粒構造の解析

飼料用米水稲新品種候補「岩手122号」の収量構成要素および穂の着粒構造の解析

Stage-dependent temperature sensitivity function predicts seed-setting rates under short-term extreme heat stress in rice

Seed-setting rate of rice (Oryza sativa L.) significantly decreases under high temperatures during the reproductive period largely due to heat-induced spikelet sterility. The effects depend largely on the timing and severity of heat stress, but the variation in the sensitivity of seed-setting rate in response to heat stress at different growth stages is not yet well simulated by most of the present crop models. To investigate the quantitative relationships between seed-setting rates of rice and various exposures of heat stress, we conducted four-year phytotron experiments with four different temperature regimes (the target maximum/minimum temperatures, 32 °C/22 °C, 35 °C/25 °C, 38 °C/28 °C and 41 °C/31 °C in 2011 and 2012; 32 °C/22 °C, 36 °C/26 °C, 40 °C/30 °C and 44 °C/34 °C in 2014 and 2015) with factorial combinations of durations (2, 4 and 6 days in 2014 and 2015; 3, 5 and 7 days in 2011; 3, 6 and 9 days in 2012) and the timings (0, 6 or 12 days after flowering), using three japonica cultivars. The duration and intensity of heat stress were quantified by the heat degree-days (HDD), defined as the temperature sum above a critical temperature value, which varied from 35 to 36 °C, depending on the cultivars. The observed seed-setting rates were well expressed as a logistic function of HDD, but the temperature sensitivity parameter varied with the timing of heat stress and the spikelet positions on the panicle. The variation in timing of flowering was apparent among upper, middle and lower parts of the panicles: 1 and 3-day delay of flowering for the spikelets on the middle and lower parts of the panicles, respectively, compared with upper ones. We therefore developed a simulation model that reflects the changes in the sensitivity of seed-setting rate to HDD to estimate the effects of heat stress with different intensities or durations at any time from flowering onward. The model with the stage-dependent parameters improved substantially the root mean square error (RMSE) and mean bias error (MBE) of seed-setting % from 20.1 and 6.0 to 7.6 and 0.2, respectively, compared to that with the stage-independent parameters. The proposed model needs to be tested under field conditions, but will be an important basis for accurate prediction of seed-setting rates in rice, which is critical for reliable estimates of crop production under climate change.

Epichloë fungal endophyte colonisation and seed quality in developing grass florets – effect of different fertiliser applications

ABSTRACTPerennial ryegrass is an important pasture, forage and turf plant, and in New Zealand, it is commonly and intentionally inoculated with selected beneficial endophyte strains. These endophytes provide enhanced traits to their host grasses with AR37, a market leading strain, conferring a broad spectrum of insect deterrence coupled with excellent animal performance. The effect of different nitrogen forms, with and without potassium, on a range of seed quality parameters, and presence of AR37, was determined. TSW and seed germination did not respond to nitrogen application. However, a combination of nitrogen and potassium reduced TSW and seed germination and increased empty seed percentage. There was no influence of spikelet position on any of the seed quality parameters measured. However, within a spikelet, there was an effect of floret position on TSW, empty seed and endophyte presence. The effect varied depending on whether nitrogen was applied as nitrate or ammonium.

Effect of Cold Pretreatment, Anthers Orientation, Spikelet Position and Donor Tiller on the Callusing Response in Barley Anther In vitro Culture

Effect of Cold Pretreatment, Anthers Orientation, Spikelet Position and Donor Tiller on the Callusing Response in Barley Anther In vitro Culture

Differences in Viscosity of Superior and Inferior Spikelets of Japonica Rice with Various Percentages of Apparent Amylose Content.

Viscosity, a crucial characteristic for rice palatability, is affected by endosperm characters. We compared correlations between differences in viscosity of japonica rice with various palatability and endosperm characters. Changes in apparent amylose and protein contents (AAC% and PC%, respectively) and amylopectin side-chain distribution and the relationship of these traits with palatability were investigated in superior and inferior spikelets of good cultivars with low amylose content from Hokkaido and common cultivars from northeastern Japan, using rapid visco analyzer characteristics and rice-grain microstructures. Significant differences occurred in PC%, AAC%, breakdown, setback, peak time, and pasting temperature of different cultivars and grain positions. Amylopectin components showed remarkable differences in grain surfaces, surface layers, and section structure between the grain varieties. Hokkaido cultivars showed better viscosity than northeastern cultivars, particularly initial stage grains. Correlation analysis indicated viscosity was mainly AAC%-dependent, whereas differences in endosperm characteristics between spikelet positions were mainly due to grain-filling temperature.

Gene interaction at seed-awning loci in the genetic background of wild rice

Seed awning is one of the important traits for successful propagation in wild rice. During the domestication of rice by ancient humans, plants with awnless seeds may have been selected because long awns hindered collection and handling activities. To investigate domestication of awnless rice, QTL analysis for seed awning was first carried out using backcross recombinant inbred lines between Oryza sativa Nipponbare (recurrent parent) and O. rufipogon W630 (donor parent). Two strong QTLs were detected in the same regions as known major seed-awning loci, An-1 and RAE2. Subsequent causal mutation surveying and fine mapping confirmed that O. rufipogon W630 has functional alleles at both loci. The gene effects and interactions at these loci were examined using two backcross populations with reciprocal genetic backgrounds of O. sativa Nipponbare and O. rufipogon W630. As awn length in wild rice varied among seeds even in the same plant, awn length was measured based on spikelet position. In the genetic background of cultivated rice, the wild alleles at An-1 and RAE2 had awning effects, and plants having both wild homozygous alleles produced awns whose length was about 70% of those of the wild parent. On the other hand, in the genetic background of wild rice, the substitution of cultivated alleles at An-1 and RAE2 contributed little to awn length reduction. These results indicate that the domestication process of awnless seeds was complicated because many genes are involved in awn formation in wild rice.

Effects of Spikelet and Grain Positions on Grain Weight and Protein Content of Different Wheat Varieties

Effects of Spikelet and Grain Positions on Grain Weight and Protein Content of Different Wheat Varieties

Genotypic variation in spike fertility traits and ovary size as determinants of floret and grain survival rate in wheat.

Spike fertility traits are critical attributes for grain yield in wheat (Triticum aestivum L.). Here, we examine the genotypic variation in three important traits: maximum number of floret primordia, number of fertile florets, and number of grains. We determine their relationship in determining spike fertility in 30 genotypes grown under two contrasting conditions: field and greenhouse. The maximum number of floret primordia per spikelet (MFS), fertile florets per spikelet (FFS), and number of grains per spikelet (GS) not only exhibited large genotypic variation in both growth conditions and across all spikelet positions studied, but also displayed moderate levels of heritability. FFS was closely associated with floret survival and only weakly related to MFS. We also found that the post-anthesis process of grain set/abortion was important in determining genotypic variation in GS; an increase in GS was mainly associated with improved grain survival. Ovary size at anthesis was associated with both floret survival (pre-anthesis) and grain survival (post-anthesis), and was thus believed to 'connect' the two traits. In this work, proximal florets (i.e. the first three florets from the base of a spikelet: F1, F2, and F3) produced fertile florets and set grains in most cases. The ovary size of more distal florets (F4 and beyond) seemed to act as a decisive factor for grain setting and effectively reflected pre-anthesis floret development. In both growth conditions, GS positively correlated with ovary size of florets in the distal position (F4), suggesting that assimilates allocated to distal florets may play a critical role in regulating grain set.