Grain-filling Rate Research Articles

DEP1 is involved in regulating the carbon-nitrogen metabolic balance to affect grain yield and quality in rice (Oriza sativa L.).

The DEP1 (dense and erect panicle 1) gene, which corresponds to the erect panicle architecture, shows a pleiotropic effect in increasing grain yield and nitrogen use efficiency (NUE) in rice. Nevertheless, it remains unclear whether the carbon−nitrogen metabolic balance changes as the dep1 allele enhances nitrogen uptake and assimilation. In this study, we generated transgenic Akitakomati plants by overexpressing dep1 and analyzed the carbon−nitrogen metabolic status, gene expression profiles, and grain yield and quality. Under either low or high nitrogen growth conditions, the carbon−nitrogen metabolic balance of dep1-overexpressed lines was broken in stem sheaths and leaves but not in grains; the dep1-overexpressed plants showed higher expressions of glutamine synthetase (GS) and glutamate synthase (GOGAT) genes than the wildtype, along with increased total nitrogen and soluble protein content in the straw at maturity. However, the ribulose-1,5-bisphosphate carboxylase/oxygenase (RUBISCO) and phosphoenolpyruvate carboxylase (PEPC) genes were downregulated in dep1-overexpressed plants, leading to a decreased carbohydrate content and carbon/nitrogen ratio. Although the unbalanced carbon−nitrogen metabolism decreased the grain-filling rate, grain setting percentage, 1000 grain weight, and grain quality in dep1-overexpressed lines, it led to increased grain numbers per panicle and consequently increased grain yield. Our results suggest that an unbalanced carbon−nitrogen metabolic status is a major limiting factor for further improving grain yield and quality in erect panicle varieties.

Amino acid content in rice grains is affected by high temperature during the early grain-filling period

Amino acid content in grains is an important nutritional quality trait in rice. High temperature can affect rice quality by accelerating grain filling. However, there is limited information available on the influence of high temperature on amino acid content in rice grains, especially under natural conditions. In this study, grain-filling traits and amino acid content in the grain of two rice cultivars (Luliangyou 996 and Lingliangyou 268) were compared between two years (2016 and 2017) with contrasting temperatures during the early grain-filling period under field conditions. Average daily mean temperature during the period of 0–5 days after full heading in 2016 (30.1 °C) was 5.4 °C higher than that in 2017. Initial, maximum, and mean grain-filling rates were 42–307% higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. The time taken to reach the maximum grain-filling rate and active grain-filling duration were 6.3–10.7 d shorter in 2016 compared to 2017 for Luliangyou 996 and Lingliangyou 268. Grain weight was equal to or significantly higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. N accumulation and N content in the grain were significantly lower in 2016 than in 2017 for both cultivars. The grain contents of all detected amino acids, except for methionine in Luliangyou 996, were significantly lower in 2016 than in 2017. Our study suggests that high temperature during the early grain-filling period can result in an accelerated grain-filling process, reduced N accumulation and content in rice grains, and consequently reduced amino acid content in the grain.

Exogenous Potassium–Instigated Biochemical Regulations Confer Terminal Heat Tolerance in Wheat

Heat stress at spike initiation and flowering is chief constraint hampering the accomplishment of yield potential in wheat crop. The present study was aimed at comparing the thermo-sensitivity of terminal stages, optimizing exogenous potassium to alleviate impacts of heat and to explore biochemical attributes triggered regulations in morphological attributes of wheat. The experiment was performed at the University of Agriculture Faisalabad, Pakistan during winter 2015–2016 and 2016–2017. The experiment was laid out in Randomized Complete Block Design under split arrangement and replicated thrice. The treatments comprised of heat stress in main plots viz. H0 = No heat imposition; H1 = Heat stress imposition from complete emergence of spike to grain filling initiation and H2 = Heat stress imposition from flowering initiation to grain filling initiation and exogenous potassium (K) concentrations in split plots viz. K0 = Control (water spray); K15 = 15 g L−1; K30 = 30 g L−1; K45 = 45 g L−1, and K60 = 60 g L−1. Under “H0,” statistically similar and relatively more activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were quantified with 45 and 60 g L−1 foliar “K.” Contrarily, significantly more SOD, POD, and CAT contents were recorded with 60 g L−1 exogenous potassium under “H1” and “H2” while significantly lesser chlorophyll a, b contents and grain yield were recorded under “H1” compared to “H0” and “H2,” whereas statistically similar and significantly more grain-filling rate (GFR) and statistically similar and significantly lesser grain filling duration (GFD) were observed under “H1” compared to “H0” “H2.” Exogenous application of K at 45 and 60 g L−1 depicted statistically similar and comparatively more chlorophyll a, b contents, GFR, GFD, and grain yield compared to control. Moreover, strong, positive, and significant association of antioxidants and chlorophyll contents with morphological attributes was observed. Conclusively, “H1” proved more deleterious compared to “H0” and “H2” and exogenous K at 60 g L−1 effectively alleviated adversities of heat. Moreover, K-mediated regulations in biochemical attributes improved morphological attributes of heat-stressed wheat crop.

Different grain-filling rates explain grain-weight differences along the wheat ear.

Thousand grain weight is one of the components determining wheat grain yield. It represents the average value of individual grain weights which depends on position within the ear and on positon within the spikelet. Our objective was to quantify the influences of individual floret anthesis date, of carpel weight at anthesis and of rate and duration of grain filling, on variation in individual final grain weight. Two bread wheat cultivars were grown in a greenhouse and their ears were sampled from anthesis through to harvest. Each ear was divided into three parts—basal, central and apical—where the two proximal grains were dissected from each of two spikelets. We analysed (i) the flowering time shift within the ear and within the spikelet; and (ii) the growth kinetics during grain filling in relation to position along the ear. For both cultivars, florets located in the central part of the ear were the first to reach anthesis followed by those in the apical part and then the basal part. Within a spikelet, the floret located nearest the rachis flowered first followed by the more distal ones. We found no significant systematic effect of flowering time-shift on final grain weight. Nevertheless, grains in the central part were heavier than the basal ones (9.75% smaller) and than the apical ones (18.25% smaller). These differences were explained mainly by differences in mean grain filling rates. Analysis of growth kinetics enabled an improved explanation of the variability of individual grain weight along the ear.

Optimizing genotype-environment-management interactions to enhance productivity and eco-efficiency for wheat-maize rotation in the North China Plain

Agricultural production is facing unprecedented challenges to ensure food security by increasing productivity and in the meantime lowering environmental risk, especially in China. To enhance productivity and eco-efficiency of the typical winter wheat-summer maize rotation simultaneously in the North China Plain (NCP), we optimized the Genotype (G) × Environment (E) × Management (M) interactions to propose the optimal agronomic management practices and cultivars for four representative sites, with the Agricultural Production Systems sIMulator (APSIM) model and detailed field trial data. The results showed that an appropriate delay in sowing date could mitigate climatic negative effects and a proper increase in sowing density could increase yield. The optimal nitrogen application rate could be 180 kg N ha−1 year−1 for maize. For the cropping system, 240 mm of irrigation for wheat and 330–390 kg N ha−1 year−1 of nitrogen application rate (150–210 kg N ha−1 year−1 for wheat and 180 kg N ha−1 year−1 for maize) were suitable to sustain high yield, resource use efficiency, and lower N2O emissions. These recommended levels were, respectively, 40% less than the current irrigation and N application rate commonly used by local farmers. The recommended management practices could increase groundwater recharge while reducing nitrogen leaching and N2O emissions without reducing yield. The maize cultivars with a long growth duration, large grain number and grain-filling rate are desirable. The desirable wheat cultivars are characterized with a medium vernalization sensitivity and high grain filling rate. The present study demonstrated an effective approach to develop sustainable intensification options for producing more with less environmental costs through optimizing G × E × M interactions.

Combined effect of shading time and nitrogen level on grain filling and grain quality in japonica super rice

There is limited information about the combined effect of shading time and nitrogen (N) on grain filling and quality of rice. Therefore, two japonica super rice cultivars, Nanjing 44 and Ningjing 3, were used to study the effect of shading time and N level on the characteristics of rice panicle and grain filling as well as the corresponding yield and quality. At a low N level (150 kg N ha−1, 150N), grain yield decreased (by 21.07–26.07%) under the treatment of 20 days of shading before heading (BH) compared with the no shading (NS) treatment. These decreases occurred because of shortened panicle length, decreased number of primary and secondary branches, as well as the grain number and weight per panicle. At 150N, in the treatment of 20 days of shading after heading (AH), grain yield also decreased (by 9.46–10.60%) due to the lower grain weight per panicle. The interaction of shading and N level had a significant effect on the number of primary and secondary branches. A high level of N (300 kg N ha−1, 300N) could offset the negative effect of shading on the number of secondary branches and grain weight per panicle, and consequently increased the grain yield in both shading treatments. In superior grains, compared with 150N NS, the time to reach 99% of the grain weight (T99) was shortened by 1.6 to 1.7 days, and the grain weight was decreased by 4.18–5.91% in 150N BH. In 150N AH, the grain weight was 13.39–13.92% lower than that in 150N NS due to the slow mean and the maximum grain-filling rate (GRmean and GRmax). In inferior grains, grain weight and GRmean had a tendency of 150N NS>150N BH>150N AH. Under shaded conditions, 300N decreased the grain weight due to lower GRmean both in superior and inferior grains. Compared with 150N NS, the milling and appearance qualities as well as eating and cooking quality were all decreased in 150N BH and 150N AH. Shading with the high level of 300N improved the milling quality and decreased the number of chalky rice kernels, but the eating and cooking quality was reduced with increased chalky area and overall chalkiness. Therefore, in the case of short term shading, appropriate N fertilizer could be used to improve the yield and milling quality of rice, but limited application of N fertilizer is recommended to achieve good eating and cooking quality of rice.

Optimal nitrogen regimes compensate for the impacts of seedlings subjected to waterlogging stress in summer maize.

A field experiment was performed to explore the compensation effects of different nitrogen (N) regimes on the growth and photosynthetic capacity in different leaf layers of the summer maize hybrid of LuYu9105 under waterlogging at the seedling stage. The results showed that waterlogging significantly decreased the maximum green leaf area (gLA) by 10.0~15.3% and 9.3~22.5%, mainly due to the reduction in the below-ear layer leaves at the silking stage in 2014 and 2015, respectively. Waterlogging also significantly decreased the ear leaf photosynthetic rate (PN), and Fv/Fm, Fv/Fo, ΦPSII and qP at the below-ear layer leaves at the mid- and late-filling stages, which was accompanied by a reduction in the duration of grain-filling (T) by 2.6~5.9%, thus resulting in a loss of grain yield by 7.0~18.5%. Interestingly, a shift in N from basal application to topdressing at the big flare stage was shown to compensate the adverse effects of waterlogging by through increased gLA and leaf photosynthetic capacity at the ear layer and the above-ear layer, as well as a greater grain-filling rate, resulting in an increase in grain yield by 9.9~27.0% and 17.8~25.8% compared to other N treatments. Therefore, this study showed that optimal nitrogen regimes during maize growth are capable of compensating for the impacts caused by waterlogging at the seedling stage.

Timing of Water Deficit Limits Maize Kernel Setting in Association With Changes in the Source-Flow-Sink Relationship.

The kernel setting of maize varies greatly because of the timing and intensity of water deficits. This variation can limit leaf productivity (source), the translocation of assimilated sugars (flow), and yield formation (sink). To explain the decline in kernel setting of maize under water deficits from the perspective of source-flow-sink, a 3-year experiment was conducted under a rain shelter. Five water regimes were studied. One regime included well-irrigated (CK) treatment. Four regimes involved water deficits: irrigation was withheld during the 6- to 8-leaf stage (V6−8), the 9- to 12-leaf stage (V9−12), the 13-leaf stage to tasseling stage (V13−T), and the silking stage to blister stage (R1−2). Water deficit effects on kernel setting began when the water deficit occurred at V9 and became more significant with time. Kernel weight was reduced by 12 and 11% when there were water deficits during V9−12 and V13−T, respectively. This was the result of reduced leaf area (limited source) and an altered vascular bundle in the ear peduncles (limited assimilate flow). The reduced vascular bundle number, rather than the ear peduncle cross-sectional area, significantly affected the final kernel weight when exposed to a water deficit prior to the silking stage. The water deficits prior to and close to the flowering stage significantly reduced ear kernel number; that is, 14 and 19% less during V13−T and R1−2, respectively, compared with the kernel number during the CK treatment. This reflects a smaller sink under water deficit conditions. Additionally, ovary size was reduced the most in the V13−T water deficit compared with other treatments. After rewatering, the water deficit before or during flowering stage continued to have residual effects on grain-filling in the late growth period. The grain-filling rate decreased under the V9−12 water deficit; the grain-filling duration shortened under the R1−2 water deficit; and both negative effects occurred under the V13−T water deficit. This study clearly indicated that (1) the water deficit during the vegetative organ rapid growth period both limited leaf source development and assimilate flow and slowed down kernel development, and (2) the water deficit just before and during flowering reduced kernel sink. Deficits at both times could retard grain-filling and reduce maize yield. The results of the present study might guide irrigation practices in irrigated maize or inform the management of sowing time in rainfed maize, to desynchronize the water deficit and the plant’s reactions to such deficits at different stages.

Characterization of the rate and duration of grain filling in wheat in southwestern China

ABSTRACTField trials were carried out during 2011–2013 in three locations on 10 wheat genotypes. Traits that were investigated included grain weight, grain-filling duration, grain-filling rates and the lag phase from flowering to the commencement of effective grain filling. The grain-filling duration and rate were fitted by Richard’s equation in thermal time (growing degree-days (GDD), base temperature 9ºC). A combined ANOVA across environments showed that the grain weight was mainly affected by genotype, while most of the other grain-filling characters were influenced by the environment and G × E interactions. Grain filling lasted between 362 to 400 GDD and included a lag phase that ranged from 67 to 86 GDD. Both the effective and maximum rates of grain filling ranged from 0.12 to 0.15 mg GDD−1 and 0.18–0.22 to GDD−1, respectively. The lag phase was positively correlated with grain weight and rates of grain filling, whereas days to anthesis were significantly negatively correlated with the lag phase and both rates of grain filling. Temperature during grain filling was negatively correlated with the lag phase. The variation in grain weight was positively associated with the rate of grain filling, which, in turn, was related to the grain number per unit area. A compensating variability existed among the genotypes in both the grain number and grain-filling rate. The study of genotypic stability demonstrated that Chuanmai42 and Chuanmai104 had high grain weight and stability among most of the grain-filling parameters, and also had high grain yield. Chuanmai42 and Chuanmai104 were the best genotypes for improving the yield potential and grain weight stability.

Grain development and endogenous hormones in summer maize (Zea mays L.) submitted to different light conditions.

Low light is a type of abiotic stress that seriously affects plant growth and production efficiency. We investigated the response mechanisms of summer maize to low light by measuring the changes in endogenous hormones in the grains and during grain filling in summer maize at different light intensities to provide a theoretical basis for the production and management of summer maize under light stress. We applied different light treatments in a field experiment as follows: S, shading from tassel stage (VT) to maturity stage (R6); CK, natural lighting in the field; and L, increasing light from VT to R6. The shading level was 60%, and the maximum illumination intensity of the increasing light treatment on cloudy days was 1600-1800μmolm-2s-1. Compared with the control, shading significantly increased the grain abscisic acid (ABA) content at 5-20days after pollination and decreased the indole acetic acid (IAA), zeatin riboside (ZR), and gibberellin (GA) contents (P < 0.05). The grain-filling rate decreased under shading conditions. Meanwhile, the grain volume, grain weight, and yield all decreased; the yields in 2013 and 2014 decreased by 61 and 60%, respectively. The grain IAA, ZR, and GA contents were increased by increasing light. The grain ABA content at 5-20days after pollination did not significantly differ from that of CK (P < 0.05). After 20days after pollination, the ABA content decreased, the grain-filling rate and the filling duration increased, and the yield increased. However, shading after anthesis increased the grain ABA content and reduced the IAA, ZR, and GA contents. Grain growth and development were inhibited, and the yield decreased. The grain ABA content decreased; the IAA, ZR, and GA contents increased; and the yield increased after increasing light. The results indicate that different light intensities regulated the levels of grains endogenous hormones, which influenced the grain-filling rate and duration, and consequently, regulated grain weight and yield.

Identification of genotypes and marker validation for grain filling rate and grain filling duration in wheat under conservation agriculture

Increase in ambient temperature beyond threshold level as predicted by global climate models may impact wheat production severely in India if it happens during grain filling stage. Grain filling rate (GFR) and grain filling duration (GFD) are critical determinant for final grain yield realization in wheat. GFR in wheat follow a slow-fast-slow pattern, however, wheat genotypes may have quantitative differences in this pattern. Ninty six diverse wheat genotypes were evaluated for GFR in two phases i.e. during first 20 days after anthesis and thereafter up to physiological maturity and grain filling duration. Out of 96 genotypes, six namely, G958, G1203, G1219, G1275, HD2985 and HDCSW18 were having high GFR during initial phase while seven genotypes viz., G949, G1081, G1124, G1159, G1204, HD3059 and HD2380 exhibited high GFR at terminal phase of grain development. Genotypes, G1263, G1207, G1423 along with some of the released varieties, HD2285, WH1105 and HD2864 were having higher GFD. Correlation between the two traits were not significant (r = -0.17959). ANOVA for GFR and GFD indicated highly significant variability among the genotypes. QTLs identified for GFR and GFD elsewhere were validated in Indian breeding material under conservation agriculture. Two SSR markers viz., XCfd42 and Xwmc500 explained about 6% and 1% variation for GFR, respectively. Similarly, already reported marker Xwmc382 was able to explain about 8% of variation for GFD in the Indian breeding material. It has been postulated from the study that by crossing the genotypes with high GFR in different grain growth stages like HD CSW 18 and HD 3059, genotypes with consistently high grain filling rate throughout the grain growth stage can be developed. The markers XCfd42 and Xwmc 382 can be further explored for fine mapping to integrate in the breeding programme for selection.

Increasing the abscisic acid level in maize grains induces precocious maturation by accelerating grain filling and dehydration

Elevated levels of abscisic acid (ABA) are closely associated with cereal grain filling under water deficit. However, grain dehydration during grain filling has received little attention. In this paper, three experiments with drought stress and exogenous ABA treatments were conducted to investigate the relationship between ABA and grain dehydration in maize (Zea mays L.) during the grain-filling period. The results indicated that exogenous ABA application and drought stress led to the same tendency of the grain ABA concentration, carbohydrate concentration and dehydration rate to increase but the moisture content to decrease. Moreover, the time to reach the maximum grain-filling rate was advanced, and the grain-filling period was shortened. In in vitro culture experiments, the sucrose-to-starch conversion was promoted, mainly influenced by sucrose synthase, ADP-glucose pyrophosphorylase (AGPase), and soluble starch synthase during the middle grain-filling stage, and the improvement in starch synthesis was possibly induced by AGPase. Correlation analysis showed that the ABA level was significantly negatively correlated with the moisture content and positively correlated with the starch level. A close and notably negative correlation was observed between the grain moisture content and starch level. In summary, adequate grain ABA promoted sucrose-to-starch conversion, shortened the duration of grain filling and accelerated grain dehydration, resulting in precocious grain maturation.

Grain filling and yield of mung bean affected by salicylic acid and silicon under salt stress

ABSTRACTTwo experiments were carried out in 2013 and 2014, to investigate changes in grain filling rate (GFR), grain filling duration (GFD) and yield of mung bean in response to salicylic acid (SA) and silicon (Si) under salt stress (0, 3, 6 and 9 dS m−1). In experiment 1, four levels of SA (0, 0.5, 1 and 1.5 mM), but in experiment 2, two levels of SA (0 and 1 mM) and Si (0 and 2 mM) were applied. In experiment 1, GFR, GFD, yield components, biological and grain yields and harvest index were decreased with increasing salt stress. Application of different levels of SA, especially 1 mM, increased GFR, but decreased GFD. In experiment 2, GFD under salinity was shorter than that under non-saline condition, resulting in comparatively smaller grains. Application of Si and particularly SA accelerated grain development under all salinity treatments. The superiority of SA treated plants in GFR, grain weight and grains per plant resulted in greater grain yield per plant under saline and non-saline conditions.

Effect of maize plant morphology on the formation of apical kernels at different sowing dates and under different plant densities

In maize (Zea mays L.), final grain yield is largely determined by kernel number at harvest. The goal of this research was to assess the source of kernel loss and identify the main factors in the process of kernel formation among maize hybrid genotypes comprising semi-compact (JH5) and compact (LD9066) genetic backgrounds (with contrasting tolerance to stand density) under field conditions. Field experiments were conducted in 2014 and 2015. Two hybrids were grown at three sowing dates (early April: SD1, early May: SD2, and late May: SD3) and under three plant densities: D1 (5.25 plants m−2), D2 (6.75 plants m−2), and D3 (8.25 plants m−2). Two sources of kernel loss were assessed and associated with 1) silks failing to emerge from the husk 7 days after silking (loss1) and 2) kernel abortion during the grain-filling period (loss2). The results demonstrated that floret number was significantly influenced by maize hybrid: the semi-compact maize hybrid JH5 had more florets than did the compact maize hybrid LD9066. However, the final kernel number per plant (FKNP) of JH5 was slightly lower than that of LD9066. JH5 had a larger value for both loss1 and loss2 than did LD9066 (22.6% vs 11.9% and 21.0% vs 12.1%, respectively). Moreover, sowing date and plant density also significantly influenced the source of kernel loss. SD1 exhibited a greater value of loss1 than did SD2 and SD3 (24.9%, 15.8% and 11%, respectively) but a lower value of loss2 than did SD2 and SD3 (10.0%, 20.6% and 19.6%, respectively). Plant density had no significant effect on loss1; however, the highest plant density (D3) resulted in the highest loss2 among three plant densities (9.4%, 15.9% and 25.9%). The dynamics of visible silking showed that JH5 requires more time (+1.5 days) to reach 50% maximum visible silks than does LD9066 and has a lower proportion of maximum visible silks at the seventh day after silking. In addition, the apical kernels of JH5 had a relatively longer Dmax (days needed to reach the maximum grain-filling rate) and greater Gmax (maximum grain-filling rate) than did those of LD9066 (+0.5 day and +3.5 mg kernel−1 d−1, respectively). However, the Wmax (kernel weight at the maximum grain-filling rate) and P (active grain-filling period) of JH5 were much lower than those of LD9066 (-6.4 mg kernel−1 and −8.2 days, respectively). Compared with the semi-compact hybrid, the compact hybrid showed an enhanced ability to resist abiotic stress tolerance, with good fertilization synchronization and a low percentage of kernel abortion. These above-mentioned traits should be considered in breeding programs to further increase the maize yield in China.

Effects of 1-Methylcyclopropene on Rice Growth Characteristics and Superior and Inferior Spikelet Development Under Salt Stress

Salinity stress hampers rice growth and development due to its osmotic, ionic, and hormonal (ethylene) stresses. High ethylene production affects inferior and superior spikelet development in rice cultivars under salt stress. 1-Methylcyclopropene (1-MCP) is an excellent ethylene inhibitor in plants. However, the effects of 1-MCP on rice growth and spikelet development under salt stress have not been studied. In this experiment, two rice cultivars, Liangyoupeijiu (LYP9, indica) and Nipponbare (NPBA, japonica), were grown in a pot culture experiment with three levels of salt stress [control (CK), 1.5 g NaCl/kg dry soil (low salt stress, LS), and 4.5 g NaCl/kg dry soil (heavy salt stress, HS)] and two 1-MCP levels (no 1-MCP and 1-MCP applied at the rice booting stage) over ten sampling times. The results showed that the application of 1-MCP significantly inhibited ethylene production in inferior spikelets of both cultivars compared with superior spikelets under salt stress. 1-MCP is more effective in increasing grain-filling rate and grain weight for inferior spikelets than for superior spikelets in both cultivars. The application of 1-MCP improved the net photosynthesis rate (Pn), stomatal conductance (gs), transpiration rate (Tr), SPAD values, and the leaf area index (LAI) of flag leaves in both cultivars compared with no 1-MCP application. 1-MCP was more effective in increasing grain-filling rate and grain weight in the LYP9 cultivar than in the NPBA cultivar under all salt stress treatments. As compared to the treatment without 1-MCP at the same salt stress level, the grain yield per plant with 1-MCP treatment increased by 35.6, 37.6, and 35.3% for CK, LS, and HS treatments, respectively, for LYP9 plants. 1-MCP treatment increased the rice grain-filling rate, plant dry matter, and yield components, such as 1000-grain weight, grain formation rate, and harvest index, of both NPBA and LYP9. These findings demonstrate the beneficial role of 1-MCP under salt stress by increasing rice growth characteristics and the development of spikelets, particularly inferior spikelets.

Diallel analysis of grain filling rate and grain filling period in tropical maize (Zea mays L.)

Grain yields of maize in the lowland tropics are generally limited by short days and high temperatures that minimize durations of incident light. Little has been published on the effects of this limiting environment on the genetics of grain filling rate (GFR), and grain filling period (GFP) in tropical maize germplasm. This study sought to address these limitations. A set of 8 elite maize inbreds of tropical origin and their 28 diallel hybrids were grown in three seasons at Waimanalo, Hawaii, USA. Seasonal differences included > 100% differences in values of photosynthetic active radiation (PAR) during grain formation. Information was sought on the performance variations and the genotype by season interactions for GFR, GFP, days to mid-silk (DTS), kernel weight, with estimates of general (GCA) and specific combining ability (SCA) and their interactions with seasons. Significant differences occurred for inbreds, hybrids, and genotype by season interactions, GCA and SCA effects and their interactions with seasons, which could be attributed primarily to the differences in PAR values among seasons in Hawaii during grain filling. Additive genetic effects predominated for GFR and GFP. Breeding approaches that take advantage of additive gene effects including hybrid breeding with evaluations in multiple Hawaii seasons may be used to alter GFR and GFP.

Mapping QTLs for grain yield components in wheat under heat stress.

The current perspective of increasing global temperature makes heat stress as a major threat to wheat production worldwide. In order to identify quantitative trait loci (QTLs) associated with heat tolerance, 251 recombinant inbred lines (RILs) derived from a cross between HD2808 (heat tolerant) and HUW510 (heat susceptible) were evaluated under timely sown (normal) and late sown (heat stress) conditions for two consecutive crop seasons; 2013–14 and 2014–15. Grain yield (GY) and its components namely, grain weight/spike (GWS), grain number/spike (GNS), thousand grain weight (TGW), grain filling rate (GFR) and grain filling duration (GFD) were recorded for both conditions and years. The data collected for both timely and late sown conditions and heat susceptibility index (HSI) of these traits were used as phenotypic data for QTL identification. The frequency distribution of HSI for all the studied traits was continuous during both the years and also included transgressive segregants. Composite interval mapping identified total 24 QTLs viz., 9 (timely sown traits), 6 (late sown traits) and 9 (HSI of traits) mapped on linkage groups 2A, 2B, and 6D during both the crop seasons 2013–14 and 2014–15. The QTLs were detected for GWS (6), GNS (6), GFR (4), TGW (3), GY (3) and GFD (2). The LOD score of identified QTLs varied from 3.03 (Qtgns.iiwbr-6D) to 21.01 (Qhsitgw.iiwbr-2A) during 2014–15, explaining 11.2 and 30.6% phenotypic variance, respectively. Maximum no of QTLs were detected in chromosome 2A followed by 6D and 2B. All the QTL detected under late sown and HSI traits were identified on chromosome 2A except for QTLs associated with GFD. Fifteen out of 17 QTL detected on chromosome 2A were clustered within the marker interval between gwm448 and wmc296 and showed tight linkage with gwm122 and these were localized in 49–52 cM region of Somers consensus map of chromosome 2A i.e. within 18–59.56 cM region of chromosome 2A where no QTL related to heat stress were reported earlier. Besides, three consistent QTLs, Qgws.iiwbr-2A, Qgns.iiwbr-2A and Qgns.iiwbr-2A were also detected in all the environments in this region. The nearest QTL detected in earlier studies, QFv/Fm.cgb-2A was approximately 6cM below the presently identified QTLs region, respectively Additionally, QTLs for physiological and phenological traits and plant height under late sown and HSI of these traits were also detected on chromosome 2A. QTL for HSI of plant height and physiological maturity were located in the same genomic region of chromosome 2Awhereas QTLs for physiological and phonological traits under late sown were located 8cM and 33.5 cM below the genomic location associated with grain traits, respectively in consensus map of Somers. This QTL hot-spot region with consistent QTLs could be used to improve heat tolerance after validation.

Effects of planting patterns and sowing densities on grain-filling, radiation use efficiency and yield of maize (Zea mays L.) in semi-arid regions

The ridge-furrow rainwater harvesting system is a valuable technique for collecting runoff water and increasing radiation use efficiency to improve crop production. Field experiments were conducted over two consecutive years (2015–16) on a loess soil in semi-arid regions of China. Three different planting densities (L: 52500 plant ha−1; M: 75000 plant ha−1; H: 97500 plant ha−1) and three different planting patterns (RF: ridge and furrow rainfall harvesting system; FM: flat planting with plastic film mulching; CP: conventional planting without plastic film) were used to measure various maize characteristics. The objectives were to enhance the water use efficiency (WUE), radiation use efficiency (RUE), and promote the grain-filling process and yields of maize. The results showed that under the same densities, there was no significant differences between the average filling rate (Gmean) and the maximum filling rate (Gmax) (P>0.05) during the normal-precipitation year (2015). However, the Gmean and Gmax in the RF and FM treatments were significantly higher than the CP treatment in dry year (2016). Under the same densities, the number of grains per row, number of kernels per ear, and kernel yield per plant of RF and FM treatments were significantly higher than those of the CP treatment. These maize yield components decreased with increased planting densities under the same planting patterns. Compared to the CP treatment, the average annual grain yield under the RF and FM treatments increased by 33.4% and 30.0%, respectively. Compared to the CP treatment, the average annual RUE in the RF and FM treatments increased by 12.4% and 11.5% before silking and increased 17.7% and 14.7% after silking, respectively. Under the RF system with a middle planting density (M-RF) promoted grain-filling rate, grain yield, yield components, WUE, and RUE. Therefore, we concluded that M-RF model is the most suitable for increases maize yield and RUE in the semi-arid regions of China.

Character association and path co-efficient analysis in wheat (Triticum aestivum L.)

The experiment was carried out with 50 wheat lines to study their mean, range, cv (%), correlation co- efficient, and path co- efficient considering 14 different morphological characters at the experimental field of Regional Wheat Research Centre (RWRC), Bangladesh Agricultural Research Institute (BARI), Gazipur during December 2010 to April 2011. Significant variation was observed among the genotypes for all characters studied. In general, genotypic correlations were higher than the phenotypic correlations. It indicates that there was an inherent association among them which was adversely influenced by the environment. The correlation coefficients showed that, seed yield was negatively and significantly correlated with days to heading (DTH), plant height (PHT), days to anthesis (DTA), days to physiological maturity (DPM), and canopy temperature at anthesis stage (CTanth.) but only negatively correlated with canopy temperature at vegetative stage (CTveg.), canopy temperature at grain filling stage (CTgf.), spikelets per spike both genotypically and phenotypically and grain per spike showed genotypically negative correlation. Path analysis showed that plant height (PHT), days to physiological maturity (DPM), canopy temperature at grain filling stage (CTgf.), and thousand grain weight (TGW) influenced seed yield directly in positive direction but days to heading (DTH), days to anthesis (DTA), grain filling duration (GFD), grain filling rate (GFR), Chlorophyll content at anthesis stage (CHLA), canopy temperature at vegetative stage (CTveg.), canopy temperature at anthesis stage (CTanth.), spikelets per spike, and grains per spike had negative direct effect on seed yield. Considering analytical findings of correlation co-efficient, path co-efficient analysis and field performance, the genotypes G 3, G 10, G 11, G 12, G13, G 21, G 29, G 35, G 38, G 40, G 46 and G 48 were found suitable for future breeding programme.Bangladesh J. Agril. Res. 42(3): 571-588, September 2017

Responses of grain filling in spring wheat and temperate-zone rice to temperature: Similarities and differences

Wheat (Triticum aestivum L.) and rice (Oryza sativa L.), which belong to the Poaceae family, are starch-grain crops, but wheat is adapted to cooler temperature conditions than rice. In this study, the difference between the two contrasting crops in grain-filling adaptability in response to temperature was investigated. Two spring wheat cultivars were grown in the Mediterranean-type environments of Western Australia and Southeast Turkey, and four temperate-zone rice cultivars were grown in several locations in Japan under irrigated conditions. Portions of the crops were enclosed under a plastic canopy to elevate the temperature after anthesis. Average temperatures during grain filling ranged from 14 to 24 °C for wheat and from 23 to 29 °C for rice. Grain yield varied from 280 to 599 g m−2 in wheat and 354 to 736 g m−2 in rice. When plant density was halved at flowering to estimate the potential grain-filling rate under an increased supply of assimilates, the grain-filling percentages [%F, observed grain weight (G)/potential grain weight (PG)] of both crops were represented by similar logistic curves of cumulative temperatures during the grain filling period. These results suggest that grain-filling responses to temperature scarcely differ between spring wheat and temperate-zone rice. G was estimated for the spring wheat and temperate-zone rice cultivars under different temperatures after anthesis using an assimilate-limited grain-potentiality model consisting of the following parameters: rate of whole-plant weight increase (ΔW/Δt), rate of potential grain dry weight increase (ΔPG/Δt) based on rate of%F (%F/Δt) and PG, and the amount of stem reserves (SP). The observed data showed that the decrease in ΔW/Δt with an increase in temperature in wheat was greater than in rice. According to the model, G started to decrease at lower temperatures in wheat than in rice, and this decrease was accelerated by lower amounts of SP. Therefore, the difference in the optimal temperatures for G during grain filling between the two crops was suggested to mainly result from the sensitivity of assimilation to high temperatures.