Grain-filling Stage Research Articles

Pseudomonas spp. Producing Antimicrobial Compounds Regulate Fungal Communities Inhabiting Wheat Crown in Southern Chile

The 2,4-Diacetylphloroglucinol (2,4-DAPG) and phenazine (PCA)-producing Pseudomonas inhibit wheat pathogens’ development, but the relationship between communities of pathogens and genotypes of these bacteria has been little studied. Relationships between wheat crown fungi associated with the presence of 2,4-DAPG and PCA-producing pseudomonads were evaluated in four commercial wheat crops located in the La Araucanía and Los Lagos Regions of Chile, during two crops seasons. Portions of the base of the first internode of the culm collected during the grain-filling stage were cultured in an artificial medium for fungal isolation, while roots of the same wheat plants and from plants collected previous harvest, and also used to assess yield and plant height, were used for the detection of 2,4-DAPG and PCA-producing Pseudomonas spp. using PCR with specific primers. Genera Phaeosphaeria, Fusarium, Rhizoctonia, and Microdochium were repeatedly isolated (52.6%, 22.1%, 7.8%, and 4.9%, respectively) and the genetic composition of 2,4-DAPG and PCA-producing Pseudomonas spp. varied between fields and sampling periods. Genetic groups A, B, D, K, L, and P associated with the phlD gene were detected. The presence of 2,4-DAPG-producing bacteria benefited crop health, relating their existence with increasing yield and plant height, and the reduction in the incidence and severity of disease caused by pathogenic microorganisms on the first internode of wheat culms.

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.

Exogenous ABA Enhances the Antioxidant Defense System of Maize by Regulating the AsA-GSH Cycle under Drought Stress

When drought occurs during the maize-filling period, the probability of yield decline increases. Abscisic acid (ABA) plays a regulatory role in physiological and metabolic activities during plant development. However, its effect on the antioxidant system of maize leaves during the grain-filling stage is unclear. Maize plants (Zhengdan958) were used as an experimental material, and ABA was sprayed on the leaves during the grain-filling stage. The plants were placed under drought conditions to analyze the relationship between the ascorbate-glutathione (AsA-GSH) cycle and hydrogen peroxide (H2O2) removal. Exogenous ABA significantly reduced the malondialdehyde content, relative electrolyte leakage, and H2O2 under drought stress. This is similar to the exogenous ABA effect on the AsA-GSH cycle. Exogenous ABA upregulated the transcription of related genes and alleviated the inhibition of drought stress on the monodehydroascorbate reductase and dehydroascorbate reductase activities, thereby further increasing the ascorbate peroxidase and glutathione reductase activities. It contributed to an increase in the AsA and GSH levels and inhibited the decrease in the AsA/dehydroascorbic acid and GSH/oxidized glutathione ratios. Therefore, exogenous ABA plays an important role in improving the antioxidant capacity and drought resistance physiology of maize by enhancing antioxidant enzyme activity and stabilizing the AsA and GSH redox state.

Effect of mineral N fertilizer and organic input on maize yield and soil water content for assessing optimal N and irrigation rates in Central Kenya

Maize ( Zea mays L.) is an important food crop in Kenya, while low and erratic rainfall, and low nutrient input mainly result in low maize yield. This study were to assess optimal nutrient and irrigation management practice for maize in central Kenya based on field experiment combined with modeling simulation. On-farm experiment with four treatments including no fertilizer (N0), N applied at dose of 100 kg ha –1 only in the form of a chemical fertilizer (N100) or combined with animal manure (N100M) or straw (N100S) has been conducting since 2013 in central Kenya. The Decision Support System for Agro-technology Transfer–Cropping System Model (DSSAT–CSM) was firstly calibrated under the relative optimal treatment N100M, and it was then evaluated for the rest three treatments for 6 maize growing seasons from 2014 to 2018. The responses of grain yield to different irrigation and fertilizer regimes were simulated using the calibrated DSSAT–CSM. The combination of fertilizer and manure (N100M) resulted in the highest yield and that of fertilizer and straw (N100S), in the highest level of soil water content in each soil layer. The model (DSSAT-CSM) successfully predicted both grain yield (normalized root mean square error, or nRMSE , of 21–37% and the index of agreement, or d , of 0.89–0.93) and changes in water content of each soil layer ( nRMSE < 20% and d > 0.70) in all treatments except N100S. The yield was most sensitive to any deficit in soil water content (dry spells) at the beginning of grain-filling stage, and the best regime for high yield, high water-use efficiency, and high agronomic efficiency comprised irrigation at 50–70 mm during that stage combined with fertilizer N at 100–120 kg ha –1 . The estimated magnitude yield gain with respect to optimal nutrition and irrigation ranged from 2 to 4 t ha –1 in different crop seasons. Optimal application of irrigation at the sensitive stage, fertilizer N, animal manure, and straw mulching holds great potential as an integrated farming practice for high grain yield and for efficient use of resources in maize cultivation in semi-arid parts of Kenya. • Optimal fertilizer practice and irrigation strategy was assessed for maize in Kenya. • The combination of mineral fertilizer, manure, and straw mulching is recommended. • DSSAT can be used to predict maize yield and soil water content in central Kenya. • Irrigation at 50 mm in early grain filling together with N at 100 kg ha –1 is optimal.

Epoxiconazole Improved Photosynthesis, Yield Formation, Grain Quality and 2-Acetyl-1-Pyrroline Biosynthesis of Fragrant Rice

Epoxiconazole is a triazole compound. However, the effects of epoxiconazole on crop productivity and quality were rarely reported. In this study, we investigated the effects of epoxiconazole application on yield formation, grain quality attributes, and 2-acetyl-1-pyrroline (2-AP) content in fragrant rice. A three-year field experiment was carried out with a fragrant rice variety, Meixiangzhan 2. At the heading stage, 0, 0.02, 0.04, 0.08, 0.16 and 0.32g/L epoxiconazole solutions were foliar applied to fragrant rice plants, respectively. The results showed that epoxiconazole application significantly increased grain yield, seed-setting rate and 1000-grain weight. Chlorophyll content and net photosynthetic rate of fragrant rice during the grain-filling stage significantly increased due to epoxiconazole application. Foliar application of epoxiconazole at 0.08g/L increased grain protein content and decreased both chalky rice rate and chalkiness area ratio of fragrant rice. Epoxiconazole also substantially increased grain 2-AP content by inducing the regulation in contents of related synthetic precursors, including proline, pyrroline-5- carboxylic acid, Δ1-pyrroline and methylglyoxal. Overall, foliar application of epoxiconazole could be used for the improvement in grain yield, grain quality and 2-AP content in fragrant rice production when applied concentration at 0.08–0.32g/L. Our findings provided the new roles of epoxiconazole in crop production.

Transparent plastic film combined with deficit irrigation improves hydrothermal status of the soil-crop system and spring maize growth in arid areas

Plastic film mulching and irrigation amount greatly affect soil hydrothermal status and spring maize (Zea mays L.) productivity in arid areas. Yet the coupled effects of film mulching with different optical properties and deficit irrigation on water and temperature variation within the soil-crop system and on plant growth in arid areas have not been well-investigated. A two-year field experiment was conducted with five treatments: 1) full irrigation without mulching (FN), 2) full irrigation with transparent plastic film mulching (FT), 3) full irrigation with black plastic film mulching (FB), 4) deficit irrigation with transparent plastic film mulching (DT), and 5) deficit irrigation without mulching (DN). The results showed that plastic film mulching significantly increased soil water in the 80–120 cm soil layer and canopy air humidity. The alternating wet-dry behavior of soil water caused by plastic film mulching was an effective water utilization strategy that increased crop water productivity. DT stimulated the alternating wet-dry behavior of soil water in the 0–80 cm layer more than the FN. This alternating behavior was characterized by relatively wet soil at the 12-leaf growth stage (V12), relatively dry soil from V12 to the grain-filling growth stage (R3), and relatively wet soil again after R3. Alternating wet-dry behavior changed from wet to dry at V12 in 2019 and was earlier than V12 in 2020. Plastic film mulching significantly increased soil temperature at the six-leaf growth stage (V6) and decreased canopy air temperature during the whole maize growing seasons. The higher net photosynthesis rate was observed at the canopy air relative humidity of 78.6%. Net photosynthesis rate decreased with increasing canopy air temperature. FT, FB, DT, and FN significantly increased grain yields over DN by 39.7–45.8%, 25.5–41.8%, 18.2–33.4%, and 9.0–17.0%, respectively, and increased net income over DN by 894–1127, 436–979, 343–844, and 166–429 USD ha–1, respectively. DT decreased net income and output/input ratio by 28.1% and 10.9% in 2019, respectively, compared with FT. However, these values were 12.3% and 4.0% in the relatively wet growing season in 2020. Deficit irrigation combined with transparent plastic film mulching can ensure an acceptable maize grain yield and net income in arid areas with limited water resources, especially in growing seasons with greater rainfall.

Improvement in winter wheat productivity through regulating PSII photochemistry, photosynthesis and chlorophyll fluorescence under deficit irrigation conditions

Deficit irrigation is critical to global food production, particularly in arid and semi-arid regions with low precipitation. Given water shortage has threatened agricultural sustainability under the dry-land farming system in China, there is an urgent need to develop effective water-saving technologies. We carried out a field study under two cultivation techniques: (1) the ridge and furrow cultivation model (R); and (2) the conventional flat farming model (F), and three simulated precipitation levels (1, 275 mm; 2, 200 mm; 3, 125 mm) with two deficit irrigation levels (150 and 75 mm). We demonstrated that under the ridge furrow (R) model, rainfall harvesting planting under 150 mm deficit irrigation combined with 200 mm simulated precipitation can considerably increase net photosynthesis rate (Pn), quantum yield of PSII (ΦPSII), electron transport rate (ETR), performance index of photosynthetic PSII (Fv/Fm′), and transformation energy potential of PSII (Fv/Fo). In addition, during the jointing, anthesis and grain-filling stages, the grain and biomass yield in the R model are 18.9 and 11.1% higher than those in the flat cultivation model, respectively, primarily due to improved soil water contents. The winter wheat fluorescence parameters were significantly positively associated with the photosynthesis, biomass and wheat production. The result suggests that the R cultivation model with irrigation of 150 mm and simulated precipitation of 200 mm is an effective planting method for enhancing Pn, biomass, wheat production, and chlorophyll fluorescence parameters in dry-land farming areas.

施氮量对宁夏引黄灌区麦后复种糜子生长、产量及氮素利用的影响

<p id="C3">The objective of this study is to clarify the growth rule, yield, and nitrogen utilization efficiency of proso millet under different nitrogen rates, the relationship between morphological characteristics and grain yield and nitrogen utilization was explored, and the suitable nitrogen rate for multiple cropping proso millet after spring-wheat in Irrigation Area of Ningxia was determined. The field experiments were conducted by single factor randomized block design, with four nitrogen rates [0 (N0), 90 (N1), 120 (N2), and 150 kg hm ^-2 (N3)] were set in 2019, and six nitrogen rates [180 (N4) and 210 kg hm ^-2 (N5) were added] in 2020. The results showed that the plant height, stem diameter, leaf area, root morphology, and dry matter accumulation at the key growth stages of proso millet were significantly promoted by nitrogen application, however, nitrogen application rate exceeded 150 kg hm ^-2, these indexes declined slightly except for the stem diameter and leaf area. With the increase of nitrogen rate, the root-shoot ratio decreased first and then increased and then decreased slightly, and it reached the minimum under N2 treatment at most growth stages. The root-shoot ratio at jointing, heading, grain-filling and maturity stage under N2 treatment were 0.119, 0.087, 0.054, and 0.052, respectively. The grain yield, 1000-grain weight, and grain number per plant were significantly increased by nitrogen application, and with the increase of nitrogen application rate, the yield increased initially then slightly decreased, and achieved the best effect in N2 and N3 treatments. The grain yields of N2 and N3 treatments were 2979.41 kg hm ^-2 and 3084.67 kg hm ^-2, respectively, which were 76.22% and 83.21% higher than those of N0 treatment. Nitrogen harvest index (NHI), nitrogen fertilizer apparent recovery rate (NRE), agronomic efficiency (NAE), and partial productivity (NPFP) under N2 treatment were 60.23%, 61.81%, 10.77 kg kg ^-1, and 24.83 kg kg ^-1, respectively. Furthermore, grain yield was significantly positively correlated with each growth index, and there was significant positive correlation between each growth index, and the root morphological characteristics were significantly positively correlated with nitrogen accumulation. These results revealed that nitrogen application could improve the root morphological characteristics of proso millet to promote the absorption of nitrogen, and further promote the growth of canopy, which was conductive to yield formation. In view of the growth, grain yield and nitrogen utilization, the reasonable nitrogen rate for multiple cropping proso millet in Irrigation Area of Ningxia was 120-150 kg hm ^-2.

Influence of meteorological parameters on wheat yield under different sowing conditions

Field experiments were conducted on the research farm of IARI, New Delhi during Rabi 2016-17 and 2017-18. Three varieties of wheat (PBW-723, HD-2967 and HD-3086) were sown on three different dates for generating different weather condition during various phenological stages of crop. Results showed that during early crop growth stages soil moisture had higher value and soil temperature had lower value and with progress of crop growth stage, the moisture in the upper layer decreased and soil temperature increased significantly as compared to the bottom layers. During tillering and jointing stage, air temperature within canopy was more and relative humidity was less while during flowering and grain filling stage, air temperature within canopy was less and relative humidity was more in timely sown crop as compared to late and very late sown crop. Radiation use efficiency and relative leaf water content had significantly higher value while leaf water potential had lower value in timely sown crop followed by late and very late sown crop. Yield had higher value in HD-3086 followed by HD-2967 and PBW-723 in all weather conditions. Canopy air temperature difference had positive value in very late sown crop particularly during flowering and grain-filling stages. This reflects in the yield. Yield was more in timely sown crop as compared to late and very late sown crop.&#x0D;

UAV-Based Hyperspectral and Ensemble Machine Learning for Predicting Yield in Winter Wheat

Winter wheat is a widely-grown cereal crop worldwide. Using growth-stage information to estimate winter wheat yields in a timely manner is essential for accurate crop management and rapid decision-making in sustainable agriculture, and to increase productivity while reducing environmental impact. UAV remote sensing is widely used in precision agriculture due to its flexibility and increased spatial and spectral resolution. Hyperspectral data are used to model crop traits because of their ability to provide continuous rich spectral information and higher spectral fidelity. In this study, hyperspectral image data of the winter wheat crop canopy at the flowering and grain-filling stages was acquired by a low-altitude unmanned aerial vehicle (UAV), and machine learning was used to predict winter wheat yields. Specifically, a large number of spectral indices were extracted from the spectral data, and three feature selection methods, recursive feature elimination (RFE), Boruta feature selection, and the Pearson correlation coefficient (PCC), were used to filter high spectral indices in order to reduce the dimensionality of the data. Four major basic learner models, (1) support vector machine (SVM), (2) Gaussian process (GP), (3) linear ridge regression (LRR), and (4) random forest (RF), were also constructed, and an ensemble machine learning model was developed by combining the four base learner models. The results showed that the SVM yield prediction model, constructed on the basis of the preferred features, performed the best among the base learner models, with an R2 between 0.62 and 0.73. The accuracy of the proposed ensemble learner model was higher than that of each base learner model; moreover, the R2 (0.78) for the yield prediction model based on Boruta’s preferred characteristics was the highest at the grain-filling stage.

The effect of water flooding at grain-filling stage on the uptake of heavy metal(loid)s by rice in slightly alkaline paddy soil.

Continuous flooding has been widely used in paddy field to decrease the accumulation of heavy metal(loid)s by rice due to their decreased solubility and bioavailability of most heavy metal(loid)s under water flooding condition. A field experiment with six drainage treatments during grain-filling stage was performed to investigate the influence of different water flooding conditions on availability of cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As), and mercury (Hg) and their accumulation by rice in alkaline paddy soil. The results showed at the end of experiment, the availability of Cd and Pb in soil with continuous flooding for above 25days after full heading significantly decreased compared with draining immediately after full heading of rice. But some increase of the As availability in soil with different water regimes was observed at 15days after beginning of experiment where the As availability was below its detection limit. Meanwhile, the concentrations of Cd and Cr both in rice grains and straws were decreased evidently with prolonged flooding at rice filling stage. The concentrations of Pb and Hg in grain were all below the detection limit, but increased in straw with draining 15days later compared with draining immediately after full heading of rice. However, water regimes during grain-filling stage had little effect on As uptake by rice in alkaline paddy soil. Moreover, this study also discovered that organic matter may played a critical role in controlling availability of heavy metal(loid)s in alkaline soil. This work demonstrated that at alkaline paddy soil, maintaining water flooding until 5days before harvest in rice grain-filling stage was an effective method to improve rice safety without decreasing yields in paddy field polluted with Cd, Cr, and As, but careful consideration is required for Pb and Hg.

Comparison of antioxidant activity assays in fresh purple waxy corn (Zea mays L.) during grain filling

Purple waxy corn is a good source of antioxidant compounds such as anthocyanins and polyphenols. Promotion of its use requires an appropriate assay to determine antioxidant activity. The aim of this study is to verify compatibility of the antioxidant activity assays by comparing five different assays in daily kernel samples of the fresh purple waxy corn during grain filling. The levels of antioxidants measured by 2,2-diphenyl-1-picrylhydrazyl, ferric reducing antioxidant power, and chemiluminescence showed significant positive correlations with the levels measured by the other assays (r = 0.761–0.893; p < 0.01) and with anthocyanin content (r = 0.798–0.924; p < 0.01). Reducing capacity of 2,2ʹ-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) and total phenolic content also showed significant correlations (r = 0.764; p < 0.01). However, during late grain filling, the levels of antioxidants measured by all methods showed strong correlations with each other (r > 0.699; p < 0.05). The inconsistencies among the measurements are largely dependent on the developmental stage of the corn kernel. The combination of at least two assays is required to ensure reliable antioxidant activity estimates, especially for early grain-filling stages. These results will inform efforts to promote fresh purple corn as a source of antioxidants.

Moderate drought alleviates the damage to grain quality at high temperatures by improving the starch synthesis of inferior grains in japonica rice

In agricultural production, temperature and moisture are important factors affecting grain yield and quality. Although moderate drought at the grain-filling stage can effectively alleviate the damage caused by high temperature, the specific regulatory mechanism driving the effect of moderate drought at the high temperature on starch synthesis is still unclear. To explore the effects and mechanisms of high temperature and moderate drought on rice starch synthesis at the grain-filling stage, the activities of enzymes and expression levels of the genes involved in starch synthesis under four different treatments involving high temperature and/or water stress (CK, HT, WS, and HT+WS) were investigated in this study. The starch synthesis of a japonica inbred rice was measured under the four treatments during the grain filling. The results show that the effects of high temperature and moderate drought on grain filling mainly occur in the inferior grains of rice. Through the regulation of enzymes involved in starch synthesis and the expression levels of their main genes, the synthesis of rice starch can be affected. Therefore, the high temperature and moderate drought were antagonistic, and moderate drought can alleviate the damage to grain quality at a high temperature by improving the starch synthesis of inferior grains in japonica rice. This study provides a basis for stress-resistance cultivation and breeding strategies of rice with high temperature tolerance.

Physiology, yield, and water use efficiency of drip-irrigated upland rice cultivars subjected to water stress at and after flowering

SummaryWater scarcity due to global warming can increase the water demand for upland rice at critical stages of crop development. However, there is little research on cultivar responses to this scenario and technologies that enhance water use efficiency (WUE). To determine the influence of water stress at and after flowering stages of drip-irrigated upland rice cultivars on physiology, yield, and WUE, a shelter experiment was conducted using a randomized block design with a split-plot arrangement of treatments. Three modern and one traditional cultivar were subjected to five irrigation managements: 100% of the field capacity considered the reference management (RM), 70 and 40% of the RM at the flowering stage, and 70 and 40% of the RM at the grain-filling stage. In general, the modern cultivars tended to maintain higher photosynthetic rate, stomatal conductance, transpiration, leaf water potential, and lower crop water stress index compared to the traditional cultivar under water stress. The WUE decreased for all cultivars under severe stress, averaging 0.55 and 0.62 kg m−3when stress occurred at flowering and grain-filling, respectively, whereas moderate stress imposed at grain-filling maintained WUE for all cultivars, averaging 1.21 kg m−3. In addition, grain yield (GY) showed a similar variation trend under drought stress as WUE, and its reduction was mainly associated with low filled grain percentage. Among the five irrigation treatments, both GY and WUE were the highest in the RM; the best cultivar recorded 9.3 Mg ha−1and 1.62 kg m−3, respectively. Findings suggest that attending to the full water demand under precision drip irrigation and appropriate cultivar selection can enhance upland rice production at significant levels.

LEAF AREA INDEX AND GRAIN YIELD OF DURUM WHEAT IN SOUTHERN SONORA, MEXICO, DURING THE SEASON 2020-2021

The objective was to determine the relationship between leaf area index (LAI) and wheat grain yield with durum cultivar CIRNO C2008, in thirty fields in the Yaqui (YV) and Mayo Valleys (MV), Sonora, Mexico, during the season 2020-2021. Field surveys were carried out to monitor crop development and to take LAI readings at different phenological stages using a linear ceptometer. Four samples of 1 m-2 in each field were harvested to calculate yield and count the spikes produced; also, grain protein and incidence of yellow berry were determined. Temperature, relative humidity, and cold units were recorded in an hourly format from 16 stations from the automated weather station network in Sonora, and which were closest to the fields. The LAI increased as the crop progressed, and had its highest expression (7.768) during the half grain-filling stage in YV, and at the end of flowering (8.109) in MV; the regression between grain yield and LAI had an R2 of 0.324. The avg. grain yield in YV was 7.95 t ha-1, while 7.24 in MV, but the latter had one less irrigation. The avg. spike number m-2 was 400 in YV and 370 in MV. The avg. grain protein content in YV was 10.49% and 39.6% for yellow berry, while in MV 11.26% and 13.8%, respectively. The overall avg. temperature during the season, relative humidity and the accumulated cold units for YV and MV were 16.96 and 16.97 °C, 68.31 and 69.13%, and 817 and 867, respectively

IDEOTYPE DESIGN FOR HIGH GRAIN YIELD POTENTIAL ON HEAT STRESS WHEAT

A wheat ideotype is represented by a set of cultivar parameters in a model, which could be optimized for best wheat performance under projected heat-tolerant conditions. Globally, heat stress significantly limits the yield. So, a major challenge of the 21st century is to achieve food supply security under a changing climate androughly a doubling in food demand by 2050. Global warming became a serious threat to crop productivity as heat stress sig nificantly reduced grain yield. Although the different traits related to high grain yield have beenidentified, the combination of traits that optimize high grain yield has not been established. The later sown experiments were exposed to higher temperatures at the critical reproductive and grain-filling stages of development. The influence of high temperatures was highest during anthesis, and with every 1% increase in average maximum temperature over the optimum of 25 degrees Celsius, grain yield was lowered by 4% to 7%. High temperature reduced yield, plant height, grain weight and days to anthesis and maturity, and increased the percentage of screenings and grain protein content. Genotypes that produced higher yield under heat stress had shorter days to flowering and maturity, higher NDVI during grain filling, greater chlorophyll content at the milk stage of grain fill, taller plants, greater grain weight and number, and lower screenings compared with the benchmark cultivar Sun top (main factors contributing to yield increase/parameters).

First report of Alternaria alternata causing brown leaf spot on wild rice (Oryza rufipogon) in China.

Oryza rufipogon Griff is a wild rice germplasm that might contain genes valuable for rice breeding. In May to June 2019, a leaf disease on wild rice (O. rufipogon cv. 'Haihong-12') was observed in a 3.3 ha field in Zhanjiang (20.93° N, 109.79° E), Guangdong, China. Early symptoms were yellow spots from the tip of leaves. Later, the spots gradually expanded downward the entire leaf to turn brown in turn. Symptoms were found in the tillering to the grain-filling stages (Supplementary Figure 1). The disease incidence on plants was between 10% and 40%. Twenty diseased leaves were collected from the field. The margin of the diseased tissues was cut into 2 mm × 2 mm pieces, surface-disinfected with 75% ethanol and 2% sodium hypochlorite for 30 s and 60 s, respectively, and rinsed three times with sterile water before isolation. The tissues were plated onto potato dextrose agar (PDA) medium and incubated at 28 °C. After 5-day incubation, grayish fungal colonies appeared on PDA. Single-spore isolation method was used to recover pure cultures for three isolates (Aas-1, Aas-2, and Aas-3). The colonies first produced light-grayish aerial mycelia, which turned dark grayish upon maturity. Conidiophores were branched. Conidia were two to four in chains, dark brown, ovoid or ellipsoid, and mostly beakless; had one to four transverse and zero to three longitudinal septa; and measured within 7.0-18.5 (average =12.5) × 3.0-8.8 (average=4.5) μm (n=30). Morphological characteristics of the isolates were consistent with the description ofAlternaria alternata(Fr.) Keissler (Simmons 2007).The internal transcribed spacer (ITS) region, partial RNA polymerase II largest subunit (RPB2) gene, translation elongation factor, and glyceraldehyde-3-phosphate dehydrogenase were amplified with primers ITS1/ITS4, RPB2-6F/RPB2-7R, EF-1α-F/EF-1α-R, and GDF1/GDR1, respectively(Woudenberg et al. 2015). Amplicons were sequenced and submitted to GenBank (accession nos. MW042179 to MW042181, MW090034 to MW090036, MW090046 to MW090048, and MW091450 to MW091452, respectively). The sequences of the three isolates were 100% identical (ITS, 570/570 bp; RPB2, 1006/1006 bp; TEF, 254/254 bp and GADPH, 587/587 bp) with those of CBS 479.90 (accession nos. KP124319, KP124787, KP125095, and KP124174) through BLAST analysis. The sequences were also concatenated for phylogenetic analysis by maximum likelihood. The isolates clustered withA. alternata CBS 479.90 (Supplementary Figure 2).The fungus associated with brown leaf spot on wild rice was thus identified asA. alternata.Pathogenicity tests were done in a greenhouse at 24°C-30°C with 80% relative humidity. Individual rice plants (cv. 'Haihong-12') with three leaves were grown in 10 pots, with around 50 plants per pot. Five pots were inoculated by spraying a spore suspension (105 spores/mL) onto leaves until runoff occurred, and another five pots were sprayed with sterile water to serve as controls. The test was done three times. Disease symptoms were found on the leaves after 7 days. The tips of the leaves turned yellow and spread downward. Then, the whole leaf turned brown and dried out, but the controls stayed healthy. The pathogen was re-isolated from infected leaves and phenotypically identical to the original isolate Aas-1 to fulfill Koch's postulates.To our knowledge, this report is the first one on A. alternata causing brown leaf spot on wild rice (O. rufipogon). The pathogen has the potential to reduce wild rice yields and future breeding should consider resistance to this pathogen.

Identification of microRNAs regulating grain filling of rice inferior spikelets in response to moderate soil drying post-anthesis

The grain filling of inferior spikelets is much less complete than that of superior spikelets in rice cultivars with large panicles and numerous spikelets and is promoted by moderate soil drying (MD) post-anthesis. A growing body of evidence has shown that microRNAs function in regulating grain development. However, little is known about the mechanism of microRNA control of grain filling of inferior spikelets in response to MD. In this study, grain filling of inferior spikelets was promoted by MD treatment in Nipponbare. Small-RNA profiling at the most active grain-filling stage was conducted in inferior spikelets under control (CK) and MD treatment. Of 521 known and 128 novel miRNAs, 38 known and 9 novel miRNAs were differentially expressed between the CK and MD treatments. Target genes of differentially expressed miRNAs were involved in multiple developmental and signaling pathways associated with catalytic activity, carbohydrate metabolism, and other functions. Both miR1861 and miR397 were upregulated by MD, leading to a decrease in OsSBDCP1 and OsLAC, two negative regulators of SSIIIa activity and BR signaling, respectively. In contrast, miR1432 abundance was reduced by MD, resulting in upregulation of OsACOT and thus an elevated content of both ABA and IAA. These results suggest that both starch synthesis and phytohormone biosynthesis are regulated by differentially expressed miRNAs in inferior spikelets in response to MD treatment. Our results suggest the molecular mechanisms by which miRNAs regulate grain filling in inferior spikelets of rice under moderate soil drying, providing potential application in agriculture to increase rice yields by genetic approaches.

A novel light interception trait of a hybrid rice ideotype indicative of leaf to panicle ratio

One of the major challenges facing rice breeding is to produce ideotype or ideal plant architecture (IPA) to improve canopy radiation use efficiency and hence grain yield. The hybrid japonica rice Jiayou Zhongke 6 (JYZK-6) is one of the benchmark cultivars with IPA characteristics, but the physio-ecological foundation of its high yield potential is still imperfectly understood. In this study, two-year field experiments were conducted using four japonica rice cultivars including JYZK-6 with contrasting canopy structures. A dynamic canopy light interception simulating device was constructed to capture canopy images representing the diurnal dynamics of solar angles throughout the grain-filling stage. Subsequently, leaf to panicle ratio (LPR), a newly developed physiological trait indicative of source-sink relations, was exploited to quantify the light distribution pattern within the rice canopy. The LPRs with high spatio-temporal resolution clearly showed the diurnal changes of light interception within the rice canopy. Genotypic differences in diurnal pattern of LPR were detected among the tested cultivars in both growing seasons, with the amplitude varying with grain-filling stages. Notably, LPR of the IPA cultivar JYZK-6 and its analogue WYJ-29, had a pattern of a V-shaped graph, peaking at sunrise and sunset while dropping to the lowest at noon during middle and late stages. Morphological measurement showed that the V-shaped pattern was associated with the height difference between flag leaf and panicle, panicle curvature, ratio of leaf area to panicle area, as well as the changing solar angles along with the progression of growth stage. This distinguishing feature of light pattern indicates that within the canopy of IPA cultivars, the leaf receives more light in the morning and afternoon whereas the panicle harvests more light at noon. It is inferred that such novel characteristics may provide the IPA cultivar with advantages of reducing midday suppression over the conventional cultivars, while more work is needed to verify this hypothesis. In summary, findings of this study offer a deeper insight into the physio-ecological processes underpinning radiation use efficiency at canopy level, and hence are valuable for breeding programs for ideotype cultivars.