Late Grain-filling Stage Research Articles

Wetting alternating with partial drying during grain filling increases lysine biosynthesis in inferior rice grain

Lysine content is a criterion of the nutritional quality of rice. Understanding the process of lysine biosynthesis in early-flowering superior grain (SG) and late-flowering inferior grain (IG) of rice would advance breeding and cultivation to improve nutritional quality. However, little information is available on differences in lysine anabolism between SG and IG and the underlying mechanism, and whether and how irrigation regimes affect lysine anabolism in these grains. A japonica rice cultivar was grown in the field and two irrigation regimes, continuous flooding (CF) and wetting alternating with partial drying (WAPD), were imposed from heading to the mature stage. Lysine content and activities of key enzymes of lysine biosynthesis, and levels of brassinosteroids (BRs) were lower in the IG than in the SG at the early grain-filling stage but higher at middle and late grain-filling stages. WAPD increased activities of these key enzymes, BR levels, and contents of lysine and total amino acids in IG, but not SG relative to CF. Application of 2,4-epibrassinolide to rice panicles in CF during early grain filling reproduced the effects of WAPD, but neither treatment altered the activities of enzymes responsible for lysine catabolism in either SG or IG. WAPD and elevated BR levels during grain filling increased lysine biosynthesis in IG. Improvement in lysine biosynthesis in rice should focus on IG.

Physiological Characteristics, Crop Growth and Grain Yield of Twelve Wheat Varieties Cultivated in the North China Plain

Climate change and water resource shortages have become important problems limiting winter wheat production in the North China Plain (NCP). Understanding the physiological characteristics of different wheat varieties and their relationship with crop growth and yield is of great importance for addressing climate change through a scientific approach, adopting reliable wheat varieties, and ensuring food production. This study was conducted throughout three winter wheat seasons from 2018 to 2021. The crop growth, physiological indicators, crop yields, and water productivity (WP) of 12 wheat varieties widely cultivated in the NCP were measured to investigate the relationships between physiological characteristics and crop yield. The results showed that among the three wheat seasons, the maximum plant height of each wheat variety was relatively stable, while the changes in maximum plant density (PDm), maximum leaf area index (LAIm), and maximum dry matter (DMm) were highly variable. The gas exchange parameters and fluorescence parameters of wheat flag leaves varied with growth stage, and certain varieties were sensitive to water stress. The wheat grain yield, seasonal crop evapotranspiration (ETa), and WP of the 12 varieties were similar in the 2019–2020 and 2020–2011 seasons and were approximately 25%, 7%, and 19% higher than those in the 2018–2019 season, respectively, in which there were consecutive cool events in the winter and spring. Generally, the grain yields were positively correlated with PDm, LAIm, DMm, ETa, the harvest index, and WP, at a significance level of 0.01. The high-yield wheat varieties had higher photosynthetic rates in the middle and late grain-filling stages. Based on these relationships, high-yield wheat varieties may be selected to address climate change in the NCP as well as other regions in the world. Considering the variations in yield and WP in the three different climatic conditions, we recommend Yingbo700, Lunxuan103, Shimai26, Shinong086, Han6172, and Hanong1412 as high-yield and drought-resistant wheat varieties to be used in the NCP.

Cell-type proteomic and metabolomic resolution of early and late grain filling stages of wheat endosperm.

The nutritional value of wheat grains, particularly their protein and metabolite composition, is a result of the grain-filling process, especially in the endosperm. Here, we employ laser microdissection (LMD) combined with shotgun proteomics and metabolomics to generate a cell type-specific proteome and metabolome inventory of developing wheat endosperm at the early (15 DAA) and late (26 DAA) grain-filling stages. We identified 1803 proteins and 41 metabolites from four different cell types (aleurone (AL), sub-aleurone (SA), starchy endosperm (SE) and endosperm transfer cells (ETCs). Differentially expressed proteins were detected, 67 in the AL, 31 in the SA, 27 in the SE and 50 in the ETCs between these two-time points. Cell-type accumulation of specific SUT and GLUT transporters, sucrose converting and starch biosynthesis enzymes correlate well with the respective sugar metabolites, suggesting sugar upload and starch accumulation via nucellar projection and ETC at 15 DAA in contrast to the later stage at 26 DAA. Changes in various protein levels between AL, SA and ETC support this metabolic switch from 15 to 26 DAA. The distinct spatial and temporal abundances of proteins and metabolites revealed a contrasting activity of nitrogen assimilation pathways, e.g. for GOGAT, GDH and glutamic acid, in the different cell types from 15 to 26 DAA, which can be correlated with specific protein accumulation in the endosperm. The integration of cell-type specific proteome and metabolome data revealed a complex metabolic interplay of the different cell types and a functional switch during grain development and grain-filling processes.

Difference in Starch Structure and Physicochemical Properties between Waxy Wheat and Non-Waxy Wheat Subjected to Temporary Heat Stress during Grain Filling

The formation process of starch in the grain is influenced by both genetic characteristics and environmental factors, which can affect starch quality. Waxy wheat Yangnuo1 (YN1) and non-waxy wheat Yangmai15 (YM15) were subjected to heat stress at the early, medium, and late grain-filling stages using artificial intelligence temperature control. Heat stress increased the short-chain content of amylopectin in both cultivars and decreased their amylose contents. The effect of heat stress on the wheat amylopectin structure was most pronounced 16–20 days after anthesis (DAA). The crystallinity and enthalpy of starch decreased, as did the swelling potential, solubility, and transmittance, but the retrogradation degree showed an opposite trend after heat stress. Compared with YM15, YN1 exhibited superior physical and chemical properties as well as anti-aging properties of starch and consequently had greater thermal stability under heat stress due to its higher degree of branching. The most sensitive stage to heat stress for yield was 6–10 DAA, which resulted in significant decreases in grain number and 1000-grain weight, followed by 16–20 DAA, which resulted in a significant decrease only in 1000-grain weight. Our study indicated that heat stress during the early stage of grain filling resulted in a decrease in both grain weight and yield, whereas during the middle stage of grain filling, it led to a decline in starch quality, especially in non-waxy wheat.

Don't panic any more: MORE PANICLES 3 increases rice yield at elevated CO2 levels.

Don't panic any more: MORE PANICLES 3 increases rice yield at elevated CO2 levels.

Influence mechanism of awns on wheat grain Pb absorption: Awns' significant contribution to grain Pb was mainly originated from their direct absorption of atmospheric Pb at the late grain-filling stage

The spike is the organ that contributes the most to lead (Pb) accumulation in wheat grains. However, as an important photosynthetic and transpiration tissue in spike, the role of awn in wheat grain Pb absorption remains unknown. A field experiment was conducted to investigate the influence mechanism of awn on grain Pb accumulation through two comparative treatments: with and without awns (de-awned treatment). The de-awned treatment decreased wheat yield by 4.1 %; however, it significantly lowered the grain Pb accumulation rate at the late filling stage (15 days after anthesis) and led to a 22.8 % decrease in grain Pb concentration from 0.57 to 0.44 mg·kg-1. Moreover, the relative contribution of awn-to-grain Pb accumulation gradually increased with the filling process, finally reaching 26.6 % at maturity. In addition, Pb isotope source analysis indicated that the Pb in the awn and grain mainly originated from atmospheric deposition, and the de-awned treatment decreased the proportion of grain Pb from atmospheric deposition by 8.9 %. Microstructural observations further confirmed that the contribution of awns to grain Pb accumulation mainly originated from their direct absorption of atmospheric Pb. In conclusion, awns play an important role in wheat grain Pb absorption at the late grain-filling stage; planting awnless or short-awn wheat varieties may be the simplest and effective environmental management measure to reduce the health risks of Pb in wheat in regions with serious atmospheric Pb contamination.

Application of multi-layer neural network and hyperspectral reflectance in genome-wide association study for grain yield in bread wheat

Grain yield (GY) is a primary trait for phenotype selection in crop breeding. Rapid and cost-effective prediction of GY before harvest from remote sensing platforms can be integrated with practical breeding activities. In this study, a natural population containing 166 wheat cultivars and elite lines was used for time-series prediction of GY using ground-based hyperspectral remote sensing. Canopy hyperspectral data (350–2500 nm) was collected at the flowering, early grain-filling (EGF), mid grain-filling (MGF), and late grain-filling (LGF) stages under four environments. GY was predicted by using full bands reflectance as input of multi-layer neural network. Genome-wide association study (GWAS) was performed using 373,106 markers from 660 K and 90 K single-nucleotide polymorphism (SNP) arrays in 166 wheat genotypes. Prediction accuracy for GY characterized by R 2 values were 0.68, 0.69, 0.76, and 0.65 at flowering, EGF, MGF, and LGF, respectively. Among the 26 loci identified by predicted GY, 13 were located in similar positions to previously reported loci related to yield, and another 13 were potentially new loci. Linear regression ( R 2 ) ranged from 0.87 to 0.94 indicating that distinct cumulative effects of favorable alleles detected by predicted GY were increasing as compared to measured GY. This study highlights the feasibility of combining remote sensing with machine learning for wheat breeding decisions and to understand the underlying genetic basis of crop yield. • The use of hyperspectral reflectance to predict wheat yield is investigated. • Higher accuracy of yield prediction at the mid grain-filling stage. • Predicted yield can detect QTLs that are consistent with the measured yield.

The end-use quality of wheat can be enhanced by optimal water management without incurring yield loss.

In China, water-saving irrigation is playing important roles in ensuring food security, and improving wheat quality. A barrel experiment was conducted with three winter wheat (Triticum aestivum L.) genotypes and two irrigation pattens to examine the effects of regulated deficit irrigation (RDI) on wheat grain yield, water-use efficiency (WUE), and grain quality. In order to accurately control the soil water content, wheat was planted in the iron barrels set under a rainproof shelter, and the soil water content in the iron barrel was controlled by gravity method. The mechanisms whereby water management influences the end-use functional properties of wheat grain were also investigated. The results revealed that RDI improved the end-use functional properties of wheat and WUE, without significant yield loss (less than 3%). Moderate water deficit (60% to 65% field capacity) before jointing and during the late grain-filling stage combined with a slight water deficit (65% to 70% field capacity) from jointing to booting increased grain quality and WUE. The observed non-significant reduction in wheat yield associated with RDI may be attributed to higher rate of photosynthesis during the early stage of grain development and higher rate of transfer of carbohydrates from vegetative organs to grains during the later stage. By triggering an earlier rapid transfer of nitrogen deposited in vegetative organs, RDI enhances grain nitrogen content, which in turn could enhance dough elasticity, given the positive correlation between grain nitrogen content and dough midline peak value. Our results also indicate that the effects of RDI on grain quality are genotype dependent. Therefore, the grain end-use quality of some specific wheat genotypes may be enhanced without incurring yield loss by an optimal water management.

Rapid prediction of winter wheat yield and nitrogen use efficiency using consumer-grade unmanned aerial vehicles multispectral imagery.

Rapid and accurate assessment of yield and nitrogen use efficiency (NUE) is essential for growth monitoring, efficient utilization of fertilizer and precision management. This study explored the potential of a consumer-grade DJI Phantom 4 Multispectral (P4M) camera for yield or NUE assessment in winter wheat by using the universal vegetation indices independent of growth period. Three vegetation indices having a strong correlation with yield or NUE during the entire growth season were determined through Pearson's correlational analysis, while multiple linear regression (MLR), stepwise MLR (SMLR), and partial least-squares regression (PLSR) methods based on the aforementioned vegetation indices were adopted during different growth periods. The cumulative results showed that the reciprocal ratio vegetation index (repRVI) had a high potential for yield assessment throughout the growing season, and the late grain-filling stage was deemed as the optimal single stage with R2, root mean square error (RMSE), and mean absolute error (MAE) of 0.85, 793.96 kg/ha, and 656.31 kg/ha, respectively. MERIS terrestrial chlorophyll index (MTCI) performed better in the vegetative period and provided the best prediction results for the N partial factor productivity (NPFP) at the jointing stage, with R2, RMSE, and MAE of 0.65, 10.53kg yield/kg N, and 8.90kg yield/kg N, respectively. At the same time, the modified normalized difference blue index (mNDblue) was more accurate during the reproductive period, providing the best accuracy for agronomical NUE (aNUE) assessment at the late grain-filling stage, with R2, RMSE, and MAE of 0.61, 7.48kg yield/kg N, and 6.05kg yield/kg N, respectively. Furthermore, the findings indicated that model accuracy cannot be improved by increasing the number of input features. Overall, these results indicate that the consumer-grade P4M camera is suitable for early and efficient monitoring of important crop traits, providing a cost-effective choice for the development of the precision agricultural system.

Improvement of Wheat Growth Information by Fusing UAV Visible and Thermal Infrared Images

To improve and enrich the wheat growth information, visible and thermal infrared (TIR) remote sensing images were simultaneously acquired by an unmanned aerial vehicle (UAV). A novel algorithm was proposed for fusing the visible and TIR images combing the intensity hue saturation (IHS) transform and regional variance matching (RVM). After registering the two images, IHS transform was first conducted to derive the Intensities of two images. Wavelet transform was then applied to the Intensities for obtaining the coefficients of low- and high-frequency sub-bands. The fusion rules of the fused image were developed based on regional correlation of wavelet decomposition coefficients. More specifically, the coefficients of low-frequency sub-bands were calculated by averaging the coefficients of two images. Regional variance was used to generate the coefficients of high-frequency sub-bands using the weighted template of a 3 × 3 pixel window. The inverse wavelet transform was used to create the new Intensity for the fused image using the low- and high-frequency coefficients. Finally, the inverse IHS transform consisting of the new Intensity, the Hue of visible image, and the Saturation of TIR image was adopted to change the IHS space to red–green–blue (RGB) color space. The fusion effects were validated by the visible and TIR images of winter wheat at the jointing stage and the middle and late grain-filling stage. Meanwhile, IHS and RV were also comparatively evaluated for validating our proposed method. The proposed algorithm can fully consider the correlation of wavelet coefficients in local regions. It overcomes the shortcomings (e.g., block phenomenon, color distortion) of traditional image fusion methods to obtain smooth, detailed and high-resolution images.

Agronomic and Physicochemical Properties Facilitating the Synchronization of Grain Yield and the Overall Palatability of Japonica Rice in East China

Understanding the agronomic and physicochemical characteristics related to grain yield and grain quality is an ongoing hotspot. In 2018 and 2019, high-yielding rice with good palatability (HYGP), high-yielding rice with poor palatability (HYPP), and low-yielding rice with good palatability (LYGP) were grown in paddy fields to explore the main traits underlying the better grain yield and overall palatability of HYGP. HYGP and HYPP demonstrated a 18.1–20.7% higher grain yield (p < 0.05) than LYGP; HYGP and LYGP gave an overall palatability from 75.2 to 77.0, higher (p < 0.05) than HYPP. The higher grain yield of HYGP compared to that of LYGP resulted from a larger sink size because of the spikelets per panicle and the higher total shoot biomass weight (p < 0.05). HYGP exhibited more (p < 0.05) panicles per m2 but lower spikelets per panicle and 1000-grain weight than HYPP and maintained a similar grain yield to HYPP. Compared with HYPP and LYGP, HYGP exhibited more (p < 0.05) biomass accumulation from heading to maturity, supported by the higher leaf area index, post-heading leaf photosynthetic rate, and SPAD values. HYGP had higher (p < 0.05) adenosine diphosphate glucose pyrophosphorylase and starch branching enzyme activities at the middle and late grain-filling stages than HYPP and LYGP. HYGP and LYGP had a lower (p < 0.05) chalky area, chalky degree, amylose content, setback, grain protein content, and prolamin content than HYPP, while it had a higher (p < 0.05) gel consistency, breakdown, and ratio of glutelin content to prolamin content. Our results suggested that optimized yield components, more biomass accumulation through improved leaf photosynthetic capacities, a lower amylose content with coordinated enzyme activities involved in starch synthesis, and a lower grain protein content with a better composition were the main traits facilitating the better grain yield and overall palatability of rice in east China.

Effects of Humic Acid Added to Controlled-Release Fertilizer on Summer Maize Yield, Nitrogen Use Efficiency and Greenhouse Gas Emission

Humic acid plays an important role in improving grain yield and reducing N losses. In order to explore the effects of humic acid added to controlled-release fertilizer on summer maize yield, nitrogen use efficiency (NUE) and the characteristics of greenhouse gas (GHG) emissions in maize farmland soil, a two-year field experiment was set up. The treatments consisted of two fertilizers: 3% humic acid added to controlled-release fertilizer (HACRF), controlled-release fertilizer (CRF) and a control (without N fertilizer, N0). The results demonstrate that the yield and NUE of summer maize were significantly increased with the addition of humic acid in N fertilizer. Compared with N0 and CRF, the yield of maize was increased by 99.1% and 5.0%, respectively. Compared with CRF, the contents of soil ammonium–nitrogen (NH4+-N) and nitrate–nitrogen (NO3−-N) in HACRF were higher during early maize growth stage but lower during the late grain-filling stage. The NUE and soil nitrogen interdependent rate of HACRF were significantly increased by 4.6–5.4% and 7.2–11.6%, respectively, across the years compared with those of CRF. Moreover, the annual cumulative N2O emissions in HACRF were decreased by 29.0% compared with the CRF. Thus, the global warming potential and greenhouse emission intensity of HACRF were significantly decreased by 29.1% and 32.59%, respectively, compared with CRF. In conclusion, adding humic acid to controlled-release fertilizer can result in higher yield and nitrogen uptake, improve nitrogen use efficiency and reduce greenhouse gas emissions, which have better yield and environmental effects.

Nitrogen application affects maize grain filling by regulating grain water relations

Grain water relations play an important role in grain filling in maize. The study aimed to gain a clear understanding of the changes in grain dry weight and water relations in maize grains by using hybrids with contrasting nitrogen efficiencies under differing nitrogen levels. The objectives were: 1) to understand the changes in dry matter and percent moisture content (MC) during grain development in response to different nitrogen application rates and 2) to determine whether nitrogen application affects grain filling by regulating grain water relations. Two maize hybrids, high N-efficient Zhenghong 311 (ZH311) and low N-efficient Xianyu 508 (XY508), were grown in the field under four levels of N fertilizer: 0, 150, 300, and 450 kg N ha–1 during three growing seasons. Dry weight, percent MC and water content (WC) of basal–middle and apical grains were investigated. The difference in the maximum WC and filling duration of basal–middle and apical grains in maize ears resulted in a significant difference in final grain weight. Grain position markedly influenced grain drying down; specifically, the drying down rate of apical grains was faster than that of basal–middle grains. Genotype and grain position both influenced the impact of nitrogen application rate on grain filling and drying down. Nitrogen rate determined the maximum grain WC and percent MC loss rate in the middle and the late grain-filling stages, thus affecting final grain weight. The use of high N-efficient hybrids, combined with the reduction of nitrogen application rate, can coordinate basal–middle and apical grain drying down to ensure yield. This management strategy could lead to a win–win situation in which the maximum maize yield, efficient mechanical harvest and environmental safety are all achieved.

Dissecting of the Deterioration in Eating Quality for Erect Panicle (Ep) Type High Yield Japonica Super Rice in Northest China

Ep type is an important morphological improvement (following dwarf breeding and ideal plant type) that has contributed to breeding super-high yielding, and shows a pleiotropic effect in increasing grain yield and also nitrogen-use efficiency (NUE) in rice. Nevertheless, it remains unclear whether Ep has adverse effects on eating quality and how it affects nitrogen uptake and assimilation. In this study, we developed a pair of near-isogenic lines (NILs) for panicle type (NIL-Ep, NIL-non Ep) in the Liaogeng 5 (LG5) and Akihikari (AKI) backgrounds. Rice plants of the NIL-Ep had higher grain numbers per panicle in the middle to bottom spike positions than plants of the NIL-non Ep. The increased grain number is not only is the key factor leading to increased yield but also is the reason for reduced the eating quality. The content of prolamin and glutelin was significantly higher in NIL-Ep, which resulted in higher hardness and worse viscosity of rice after cooking. In addition, the activity of several essential enzymes catalyzing nitrogen metabolism was higher in the NIL-Ep line grains than in the NIL-non Ep, especially from the mid to late grain filling stage. Based on these results, we conclude that Ep positively regulates grain protein accumulation, primarily through enhancing the activity of enzymes involved in nitrogen assimilation and redistribution during the mid to late grain-filling stage, resulting in excessive accumulation of grain protein and decreased eating quality.

In situ measurements of winter wheat diurnal changes in photosynthesis and environmental factors reveal new insight into photosynthesis improvement by super-high-yield cultivation

In past 30 years, the wheat yield per unit area of China has increased by 79%. The super-high-yield (SH) cultivation played an important role in improving the wheat photosynthesis and yield. In order to find the ecophysiological mechanism underneath the high photosynthesis of SH cultivation, in situ diurnal changes in the photosynthetic gas exchange and chlorophyll (Chl) a fluorescence of field-grown wheat plants during the grain-filling stage and environmental factors were investigated. During the late grain-filling stage at 24 days after anthesis (DAA), the diurnal changes in net CO2 assimilation rate were higher under SH treatment than under high-yield (H) treatment. From 8 to 24 DAA, the actual quantum yield of photosystem II (PSII) electron transport in the light-adapted state (ΦPSII) in the flag leaves at noon under SH treatment were significantly higher than those under H treatment. The leaf temperature, soil temperature and soil moisture were better suited for higher rates of leaf photosynthesis under SH treatment than those under H treatment at noon. Such diurnal changes in environmental factors in wheat fields could be one of the mechanisms for the higher biomass and yield under SH cultivation than those under H cultivation. ΦPSII and CO2 exchange rate in wheat flag leaves under SH and H treatments had a linear correlation which could provide new insight to evaluate the wheat photosynthesis performance under different conditions.

Glutathione and ethylene biosynthesis reveal that the glume and lemma have better tolerance to water deficit in wheat

As senescence progresses, the sensitivity of wheat organs to plant hormones during the grain-filling stages cannot be ignored. Especially under water deficit situation, non-leaf organs (spikes) have better photosynthesis and drought-tolerance traits than flag leaves. However, the mechanism of ethylene synthesis in wheat organs under water deficit remains unclear. We have studied the influence of water deficit in wheat flag leaves and spike bracts on photosynthetic parameters and on the expression of key enzymes involved in the ethylene biosynthesis pathway during the late grain-filling stages. More stable chlorophyll content (Chl), maximum PSII quantum yield (Fv/Fm), nonphotochemical quenching (NPQ) and maximal efficiency of PSII photochemistry under light adaptation (Fv’/Fm’) were observed in the spike bracts than that in the flag leaves during the late grain-filling stages. In addition, the activity of glutathione reductase (GR), γ-glutamylcysteine synthetase (γ-ECS), 1-aminocyclopropane-1-carboxylic (ACC) acid synthase (ACS), and ACC oxidase (ACO) induced ethylene synthesis and influenced plant growth. Further analysis of genes encoding cysteine-ethylene related proteins (γ-ECS, GR, ACO, ACS1, and ASC2) demonstrated that ear organs and flag leaves exhibited different expression patterns. These findings will facilitate future investigations of the regulatory senescence response mechanisms of cysteine interaction with ethylene in wheat under conditions of drought stress.

LPS1, Encoding Iron-Sulfur Subunit SDH2-1 of Succinate Dehydrogenase, Affects Leaf Senescence and Grain Yield in Rice.

The iron-sulfur subunit (SDH2) of succinate dehydrogenase plays a key role in electron transport in plant mitochondria. However, it is yet unknown whether SDH2 genes are involved in leaf senescence and yield formation. In this study, we isolated a late premature senescence mutant, lps1, in rice (Oryza sativa). The mutant leaves exhibited brown spots at late tillering stage and wilted at the late grain-filling stage and mature stage. In its premature senescence leaves, photosynthetic pigment contents and net photosynthetic rate were reduced; chloroplasts and mitochondria were degraded. Meanwhile, lps1 displayed small panicles, low seed-setting rate and dramatically reduced grain yield. Gene cloning and complementation analysis suggested that the causal gene for the mutant phenotype was OsSDH2-1 (LOC_Os08g02640), in which single nucleotide mutation resulted in an amino acid substitution in the encoded protein. OsSDH2-1 gene was expressed in all organs tested, with higher expression in leaves, root tips, ovary and anthers. OsSDH2-1 protein was targeted to mitochondria. Furthermore, reactive oxygen species (ROS), mainly H2O2, was excessively accumulated in leaves and young panicles of lps1, which could cause premature leaf senescence and affect panicle development and pollen function. Taken together, OsSDH2-1 plays a crucial role in leaf senescence and yield formation in rice.

Wheat ear counting using K-means clustering segmentation and convolutional neural network

BackgroundWheat yield is influenced by the number of ears per unit area, and manual counting has traditionally been used to estimate wheat yield. To realize rapid and accurate wheat ear counting, K-means clustering was used for the automatic segmentation of wheat ear images captured by hand-held devices. The segmented data set was constructed by creating four categories of image labels: non-wheat ear, one wheat ear, two wheat ears, and three wheat ears, which was then was sent into the convolution neural network (CNN) model for training and testing to reduce the complexity of the model.ResultsThe recognition accuracy of non-wheat, one wheat, two wheat ears, and three wheat ears were 99.8, 97.5, 98.07, and 98.5%, respectively. The model R2 reached 0.96, the root mean square error (RMSE) was 10.84 ears, the macro F1-score and micro F1-score both achieved 98.47%, and the best performance was observed during late grain-filling stage (R2 = 0.99, RMSE = 3.24 ears). The model could also be applied to the UAV platform (R2 = 0.97, RMSE = 9.47 ears).ConclusionsThe classification of segmented images as opposed to target recognition not only reduces the workload of manual annotation but also improves significantly the efficiency and accuracy of wheat ear counting, thus meeting the requirements of wheat yield estimation in the field environment.

Use of NDVI for indirect selection of high yield in tropical rice breeding

Plant breeders evaluate large numbers of breeding lines/accessions and measure various traits in the field in order to identify and select elite genotypes with high yield. Therefore, information on highly correlated yield-related traits and simple high-throughput methods to predict grain yield would be useful for rice breeders. The objective of this study was to examine the usefulness of various traits as indirect selection criteria for high yield in tropical rice breeding, with an emphasis on rapid and non-destructive measurements. We evaluated a wide range of germplasm, including popular varieties, elite genotypes, and donor parents, in the irrigated rice breeding program at the International Rice Research Institute, in the Philippines, during the 2015 wet season and 2016 dry season. We measured the normalized-difference vegetation index (NDVI), leaf chlorophyll content (SPAD value), agronomic traits, and grain yield. Harvest index, NDVI at the heading and late grain-filling stages, and SPAD value at the late grain-filling stage were significantly correlated with yield during the wet season, whereas plant height, panicle length, and NDVI from panicle initiation to the booting stage during the dry season. Our results indicate that pre-harvest analysis of primary and secondary traits such as NDVI has potential for selecting high-yielding accessions in tropical rice breeding programs. By using low-cost portable equipment, NDVI measurements could be incorporated into breeding programs. Trait associations with yield differed between the dry and wet seasons, which has important implications for breeding new varieties and germplasm evaluation in different seasons.

Improving grain yield and protein concentration of maize (Zea mays L.) simultaneously by appropriate hybrid selection and nitrogen management

The simultaneous improvement of grain yield and protein concentration in crop production is an important global challenge. In maize, genotype selection and nitrogen (N) management are potential methods to improve grain yield and protein concentration. A field experiment was conducted in 2015–2016 in the North China Plain to evaluate the response of grain yield and protein concentration of different modern hybrids (XY1266, ZD958 and DH618) under different N rates (0–259 kg ha−1). The highest grain dry matter and protein concentration were observed in DH618. The averaged maximal grain dry matter over the 2 years was 10.3 Mg ha−1 for DH618, 6.1 % higher than for ZD958 (9.7 Mg ha−1) and 9.9 % higher than for XY1266 (9.4 Mg ha−1), and the maximal grain protein concentration in DH618 was 8.6 %, 11.1 % higher than for XY1266 (7.8 %) and 10.1 % higher than for ZD958 (7.9 %). DH618 had higher post-silking biomass accumulation, a stable high harvest index (HI), and higher post-silking N uptake as well as N harvest index (NHI) compared to the other two hybrids, meanwhile without reducing N remobilization efficiency (NRE). In DH618, high leaf N concentration after silking facilitated a higher rate of photosynthesis, further leading to greater post-silking biomass and N accumulation, and quickly remobilization of leaf N at late grain-filling stage improved the NRE and NHI. Together with choosing the right hybrid, optimisation of N management with split N application as well as appropriate N rate taking into account the residual soil mineral N could ensure both high grain dry matter and increased protein concentration in maize.