High-yielding Rice Research Articles

Genetic Mapping of Grain Shape Associated QTL Utilizing Recombinant Inbred Sister Lines in High Yielding Rice (Oryza sativa L.)

Grain shape is a key factor for yield and quality in rice. To investigate the genetic basis of grain shape in the high-yielding hybrid rice variety Nei2You No.6, a set of recombinant inbred sister lines (RISLs) were used to map quantitative trait loci (QTLs) determining grain length (GL), grain width (GW), and length-width ratio (LWR) in four environments. A total of 91 medium/minor-effect QTL were detected using a high-density genetic map consisting of 3203 Bin markers composed of single nucleotide polymorphisms, among which 64 QTL formed 15 clusters. Twelve of 15 clusters co-localized with QTL previously reported for grain shape/weight. Three new QTL were detected: qGL-7a, qGL-8, and qGL-11a. A QTL cluster, qLWR-12c/qGW-12, was detected across all four environments with phenotypic variation explained (PVE) ranging from 3.67% to 11.93%, which was subsequently validated in paired lines of F17 progeny and tightly linked marker assay in F10 generation. Subsequently, 17 candidate genes for qLWR-12c/qGW-12 were detected in the 431 Kb interval utilizing bulk segregant analysis (BSA). Among these, OsR498G1222170400, OsR498G1222171900, OsR498G1222185100, OsR498G1222173400, and OsR498G1222170500 were the best candidates, which lays the foundation for further cloning and will facilitate high-yield breeding in rice.

Effect of flag leaf length of erect panicle rice on the canopy structure and biomass production after heading

ABSTRACT Increasing the yield potential of rice (Oryza sativa) is the main objective of breeders and cultivators engaged in rice improvement programs. Erect panicle (EP) rice is generally high-yielding with panicles that remain non-curved until maturation. The aim of our study was to evaluate the association of agronomic traits with rice productivity in EP rice. Here, we used the recombinant inbred lines (RILs), crosses between Liaojing5 (erect panicle japonica type) and Wanlun422 (high-yielding indica type). The yield varied among the RILs, and the flag leaf length of EP RILs was negatively correlated with the yield; however, the correlation was not significant in the non-EP RILs. The flag leaf length of the EP RILs was also negatively correlated with biomass increase during the late ripening stage. This may reflect the canopy structure of the EP RILs with short flag leaves which had a larger leaf area index in the lower strata. Additionally, the chlorophyll content in the lower leaf significantly differed among the EP RILs with flag leaves of different lengths, resulting in a higher photosynthetic ability of the lower leaf of EP RILs with short flag leaves. In the present study, an EP line, which has the shortest flag leaf, showed a higher yield than Wanlun422 in both years. EP RILs with short flag leaves might show a higher canopy photosynthetic rate in the later ripening stage; therefore, this trait could be a potential phenotypic marker for achieving high yield of EP rice.

Agronomic and socio-economic assessment of the introduction of a rice-based mixed cropping system to Cuvelai seasonal wetland system in northern Namibia

ABSTRACT In the semi-arid regions of southern Africa, around the borders of Angola with Namibia, the Cuvelai seasonal wetland system is formed by floods during the rainy season. The objective of the present study was to assess the effects of introduction of a rice-based mixed cropping system to the seasonal wetlands (ondombe in the local language) from agronomic, social, and economic perspectives. For this purpose, we used a simple methodology with a multidisciplinary approach for yield and household survey and scenario analysis in northern Namibia. The yield survey revealed that in ondombe, rice showed a higher yield performance than that of pearl millet and sorghum, even in a drought year. The farm household survey showed that introducing a rice-based mixed cropping to ondombe could help local farmers enhance crop productivity by reducing labour and providing high rice yield. In addition, scenario analysis based on the yield and household surveys conducted in these regions suggested that the introduction of the mixed cropping system to ondombe could compensate for one-fourth of the governmental urgent food import budget even in drought years. Therefore, this system is an effective option for sustainable agricultural production and environmental management in the studied region.

Methane mitigation is associated with reduced abundance of methanogenic and methanotrophic communities in paddy soils continuously sub-irrigated with treated wastewater

Herein, we examined emissions of CH4 and the community structures of methanogenic archaea and methanotrophic bacteria in paddy soils subjected to a novel irrigation system, namely continuous sub-irrigation with treated wastewater (TWW). This system has recently been developed by our group to effectively reuse TWW for the cultivation of protein-rich rice. The results showed that, despite not using mineral fertilisers, the wastewater reuse system produced a rice yield comparable to that of a conventional cultivation practice and reduced CH4 emissions from paddy fields by 80%. Continuous sub-irrigation with TWW significantly inhibited the growth of methanogens in the lower soil layer during the reproductive stage of rice plants, which was strongly consistent with the effective CH4 mitigation, resulting in a vast reduction in the abundance of methanotrophs in the upper soil layer. The compositions of the examined microbial communities were not particularly affected by the studied cultivation practices. Overall, this study demonstrated that continuous sub-irrigation with TWW was an effective method to produce high rice yield and simultaneously reduce CH4 emissions from paddy fields, and it also highlighted the potential underlying microbial mechanisms of the greenhouse gas mitigation.

多収水稲品種「きたげんき」後代４系統の収量及び生育特性

多収水稲品種「きたげんき」後代４系統の収量及び生育特性

CRISPR/Cas9 Guided Mutagenesis of Grain Size 3 Confers Increased Rice (Oryza sativa L.) Grain Length by Regulating Cysteine Proteinase Inhibitor and Ubiquitin-Related Proteins.

Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein (Cas9)-mediated genome editing has become an important way for molecular breeding in crop plants. To promote rice breeding, we edited the Grain Size 3 (GS3) gene for obtaining valuable and stable long-grain rice mutants. Furthermore, isobaric tags for the relative and absolute quantitation (iTRAQ)-based proteomic method were applied to determine the proteome-wide changes in the GS3 mutants compared with wild type (WT). Two target sites were designed to construct the vector, and the Agrobacterium-mediated method was used for rice transformation. Specific mutations were successfully introduced, and the grain length (GL) and 1000-grain weight (GWT) of the mutants were increased by 31.39% and 27.15%, respectively, compared with WT. The iTRAQ-based proteomic analysis revealed that a total of 31 proteins were differentially expressed in the GS3 mutants, including 20 up-regulated and 11 down-regulated proteins. Results showed that differentially expressed proteins (DEPs) were mainly related to cysteine synthase, cysteine proteinase inhibitor, vacuolar protein sorting-associated, ubiquitin, and DNA ligase. Furthermore, functional analysis revealed that DEPs were mostly enriched in cellular process, metabolic process, binding, transmembrane, structural, and catalytic activities. Pathway enrichment analysis revealed that DEPs were mainly involved in lipid metabolism and oxylipin biosynthesis. The protein-to-protein interaction (PPI) network found that proteins related to DNA damage-binding, ubiquitin-40S ribosomal, and cysteine proteinase inhibitor showed a higher degree of interaction. The homozygous mutant lines featured by stable inheritance and long-grain phenotype were obtained using the CRISPR/Cas9 system. This study provides a convenient and effective way of improving grain yield, which could significantly accelerate the breeding process of long-grain japonica parents and promote the development of high-yielding rice.

Yield of irrigated rice affected by asymptomatic disease in a long-term intensive monocropping experiment

Sustained high yields of rice (Oryza sativa L.) are required in intensively cropped, irrigated systems to ensure food security and avoid expansion of cultivation into natural ecosystems. We examined whether good management practices and adapted cultivars could maintain high yields during 15 years (2001–2015) of continuous rice cultivation with three crops per year in the dry season (DS), early wet season (EWS), and late wet season (LWS). Results are for the highest-yielding fertilizer N rate of 195 kg N ha–1 in DS and 90 kg N ha–1 in EWS and LWS at the long-term continuous cropping experiment (LTCCE) in the Philippines. Our study addressed two critical questions remaining after previously reported research in the LTCCE: Can DS yield be sustained at >80 % of the climate- and genotype-specific yield potential, and can yield be increased in wet seasons? Management in DS, when cropping was synchronized with surrounding fields, controlled diseases and maintained yield at >80 % of simulated yield potential during 15 years. In EWS and LWS, when cropping was not synchronized with surrounding fields, tungro viruses were transmitted by insects from surrounding fields into the experiment. Management and adapted cultivars within the experiment did not prevent yield loss associated with reduced spikelet filling, which was attributed largely to tungro disease. In EWS, when planting was earlier than surrounding fields, yields were about 60–80 % of yield potential. In LWS, when planting was later than surrounding fields, yields declined to <65 % of yield potential. Enzyme-linked immunosorbent assay confirmed high infection in EWS and LWS with rice tungro spherical virus, which was not accompanied by symptoms of plant yellowing and stunted growth. In DS, when tungro was negligible, good management with adapted cultivars consistently minimized yield loss from nutrient deficiencies, soil problems, pathogens, and pests. However, good management with adapted cultivars could not maintain a small yield gap when tungro viruses were transmitted from infected surrounding fields into the experiment. In such case, closing the yield gap requires management interventions to reduce the pathogen and vector in surrounding fields. Negligible visible symptoms on most tungro-infected plants highlight the ease with which a biotic stress can be overlooked in experiments and growers’ fields.

Evaluation of safe alternative wetting &amp; drying and its influence on growth, yield and water use of the efficiency of rice (Orzya sativa l.)

Due to the increase in scarcity of freshwater resources available for irrigated agriculture and escalating demand for food around the world, in the future, it will be necessary to produce more food with less water. Due to inadequate or unevenly-distributed rainfall, irrigation is essential to high rice yields. A field experiment of Alternative Wetting and Drying Irrigation (AWDI) was conducted during kharif season 2014 &amp; 2015 at Soil &amp; Water Management Research Institute, Tamil Nadu Agricultural University, Thanjavur, Tamil Nadu, India. The treatments ranged from delayed irrigations of T1 to T6 (10, 15, 20 cm depletion of water level below the ground level, 15cm depletion of water up to maximum tillering, up to panicle initiation &amp; up to 10 days prior to harvest) and continuous submergence (T7) of field irrigation water denoting the application of 5 cm flooded water condition, when the water level in the perforated PVC pipe fell at 10, 15 and 20 cm below ground level respectively. There was a significant (5% level) consequence of plant height, productive tillers, filled grains, yield and Water Use Efficiency (WUE) due to the influence of AWDI. The highest yield (5981 kg/ha) and WUE (7.56 kg/ha/mm) was recorded in treatment T1. Longer water stress resulted in the loss of grain yield to the tune of 500 to 1000 kg/ha. This study found that in sandy loam soil at 10cm depletion of ponded water produced maximum yield (5809 kg/ha, besides the highest B.C ratio of 2.02) and WUE (7.56 kg/ha mm).

Alternative fertilizer and irrigation practices improve rice yield and resource use efficiency by regulating source-sink relationships

Abstract Understanding the inherent characteristics based on leaf and root source and grain sink under an improved cultivation practice is important to achieve both high grain yield and resource use efficiency in paddy rice. A field experiment to investigate the characteristics was conducted across two years using Wuyunjing24 with five cultivation practices including no nitrogen (N) application (0 N), local farmers' practice (LFP), and three improved cultivation practices (ICPs) consisting of improved fertilizer N practice and higher plant density (ICP1), the same practices as ICP1 but with alternate wetting and moderate drying (AWMD) rather than with the continuous flooding (CF) irrigation (ICP2), and the same practices as ICP2 but plus organic fertilizer application (ICP3). The results showed that all three ICPs could synchronously increase grain yield and resource use efficiency, and the increase was the most for ICP3 and followed by ICP2, when compared with LFP. The total number of spikelets, shoot and root biomasses, total leaf area index (LAI), effective LAI, grain weight-leaf ratio, specific leaf N content, and leaf photosynthetic rate, zeatin and zeatin riboside contents in panicles, leaves and roots, and the activities root of spikelets (the ratio of root activity to spikelet number) during grain filling were significantly increased with the improvement in cultivation practices. The results suggest that the improved cultivation practices are useful to achieve high yield and high resource use efficiency through improving source and sink characteristics and coordinating their relationships.

Primary Macro Nutrient Content, Root Growth, and Crop Growth Analysis of Local Rice Varieties with Intermittent and Continuous Flooding Irrigation

An Intermittent irrigation method of rice cultivation aims to reduce water requirements. In Indonesia local rice varieties have the potential to produce high-yielding rice with the itermittent irrigation method to meet food needs in Indonesia. The study about Nutrient uptake, root development, and crop growth analysis of several local rice varieties with intermittent irrigation method aims to determine the suitability of intermittent and continuous flooding irrigation techniques on local rice varieties and to study the response of various local rice varieties to the Nutrient uptake, root development, and crop growth analysis. The research has been conducted on the experimental field of the Faculty of Agriculture Universitas Muhammadiyah Yogyakarta. The method used was the experimental method carried out with field research with an 4 x 2 factorial design of the treatment arranged in a Randomized Completely Block Design with 3 replications. The first factor was rice varieties which consist of 4 varieties, i.e. Rojolele, Pandanwangi, Mentik Wangi, and Ciherang. The second factor was the method of irrigation consisting of 2 kinds, i.e. intermittent irrigation and continuous flooding. Data was analysed with analysis of variance and Duncan’s Multiple Range Test at α=5%. The results showed that rice varieties had different responses to macro nutrient uptake. The number of productive tillers of the Cianjur, Rojolele genjah, and Ciherang varieties is greater than the Mentikwangi variety, while the total number of tillers of the Rojolele variety is even greater than the Mentikwangi variety. SRI irrigation can increase the harvest index, whereas conventional irrigation has a higher Crop Growth Rate than SRI irrigation.

Field-level factors for closing yield gaps in high-yielding rice systems of Uruguay

Yield gap assessments at the field-level are key for developing management practices to increase crop production in a sustainable manner. Although rice is an important food crop worldwide, yield gaps remain less investigated in Latin American rice systems. In this study, we evaluated field-level factors for closing yield gaps (based on attainable farm yield, defined as the mean of top 10 % of farmers) for rice production in Uruguay using crop management and yield records from 2012 to 2017, covering approximately 70,000 ha per year (40 % of total rice area). The mean annual attainable yield gap ranged from 16 % to 22 % in fields with non-hybrid cultivars (90 % of planted area) and from 14 % to 22 % in fields with hybrid rice (10 % of planted area). Early seeding was identified as the most influential factor for reducing yield gaps in both systems, followed by N rate. Stand establishment was also important for closing yield gap in non-hybrid fields, while rotation with improved pasture was important in hybrid fields. When variables were categorized as input-related, manageable, or non-manageable, on average manageable factors (e.g. early planting and stand establishment) were more important than input-related factors (e.g. seed or fertilizer rate). This study highlights a simple, self-contained method using large field-level datasets to quantify yield gaps and develop strategies for improving agricultural productivity.

OsmiR396/growth regulating factor modulate rice grain size through direct regulation of embryo-specific miR408.

microRNAs (miRNAs) are promising targets for crop improvement of complex agricultural traits. Coordinated activity between/among different miRNAs may fine-tune specific developmental processes in diverse organisms. Grain size is a main factor determining rice (Oryza sativa L.) crop yield, but the network of miRNAs influencing this trait remains uncharacterized. Here we show that sequestering OsmiR396 through target mimicry (MIM396) can substantially increase grain size in several japonica and indica rice subspecies and in plants with excessive tillers and a high panicle density. Thus, OsmiR396 has a major role related to the regulation of rice grain size. The grain shape of Growth Regulating Factor8 (OsGRF8)-overexpressing transgenic plants was most similar to that of MIM396 plants, suggesting OsGRF8 is a major mediator of OsmiR396 in grain size regulation. A miRNA microarray analysis revealed changes to the expression of many miRNAs, including OsmiR408, in the MIM396 plants. Analyses of gene expression patterns and functions indicated OsmiR408 is an embryo-specific miRNA that positively regulates grain size. Silencing OsmiR408 expression (miR408KO) using CRISPR technology resulted in small grains. Moreover, we revealed the direct regulatory effects of OsGRF8 on OsMIR408 expression. A genetic analysis further showed that the large-grain phenotype of MIM396 plants could be complemented by miR408KO. Also, several hormone signaling pathways might be involved in the OsmiR396/GRF-meditated grain size regulation. Our findings suggest that genetic regulatory networks comprising various miRNAs, such as OsmiR396 and OsmiR408, may be crucial for controlling rice grain size. Furthermore, the OsmiR396/GRF module may be important for breeding new high-yielding rice varieties.

Effects of fan volute structure on airflow characteristics in rice combine harvesters

Aim of study: Selecting a proper fan for the rice combine harvesters to get a good cleaning performance when harvesting high yield rice. Area of study: Jiangsu Province, China.Material and methods: Three potential multi-duct fans were designed, and the computational fluid dynamics and hot wire anemometer technology were utilized to learn the airflow and pressure variation inside the fan with perforated plates at the outlet ducts as cleaning loads. Then, the fan with the best performance was selected and a multi-duct cleaning test-bed was developed. The variation of the corresponding airflow velocity in the cleaning system was analyzed and the ideal airflow velocity in different section of the sieve was clarified. Finally, a field experiment was carried out.Main results: For a rice combine harvester with a feed rate of 7 kg/s (material other than grain + grain), the requested airflow rates inside the cleaning shoe was about 3.0 m3/s. The ideal airflow velocity in different section of the cleaning shoe was 8-9 m/s at upper duct, 4-6 m/s at the middle section, and 3-4 m/s at the tail section; large improvement in cleaning performance was achieved with the designed fan.Research highlights: The airflow velocity decreased as the cleaning loads at the duct increased. The fan with the averaged airflow velocity ≥7 m/s at the upper duct under different cleaning loads, and the airflow velocity at the lowest duct ≥ 9 m/s, is favorable for forming a blowing airflow in the tail sieve and is good for grain stratification.

Participation in farmers' organization and production efficiency: empirical evidence from smallholder farmers in Bangladesh

PurposeFarmer organizations (FOs) can elevate many of the production- and marketing-related challenges by ensuring access to technology, farming information and loan for inputs and mechanization. This study assesses the major factors that affect the participation in FOs by the smallholder rice farmers in Bangladesh and evaluates the impacts of the participation on rice yield and production efficiency.Design/methodology/approachThe present study used primary data collected from 1,000 smallholder rice farmers in northwest Bangladesh, consisting of 250 farmers those participated in an organization. This study utilized a sample selection stochastic production frontier (SPF) method, a combination of the conventional SPF and the Heckman's sample selection model, to control for biases stemming from observed and unobserved attributes.FindingsThis study demonstrates that participation in an organization is significantly affected by smallholder rice farmers' education, occupation, family size, household income, land ownership and the location where they reside. At the same time, the participation status affects the productivity of smallholder farmers. Findings indicate that farmers who participated in an organization had higher rice yield (11% more) and were technically more efficient (1.4 percentage points higher) compared to farmers who did not participate.Research limitations/implicationsSince this study was carried out with representative sampled farmers from northwest Bangladesh, the findings may not represent all farmers' perceptions of FOs in the country.Originality/valueEven though more than 200,000 FOs are currently in operation, knowledge regarding the effectiveness of Bangladesh's FOs is limited. Notably, this study used a relatively new method, sample selection SPF model, to investigate the impact of FOs on the production efficiency of smallholder rice farmers in northwest Bangladesh. Therefore, this study contributes to the literature in elucidating the factors affecting participation in FOs and its impact on rice yield and efficiency. Since FOs have been somewhat ineffective in their role as service providers in Bangladesh, this study’s results will guide policymakers to intervene more successfully regarding the changes needed.

High yields of hybrid rice do not require more nitrogen fertilizer than inbred rice: A meta‐analysis

AbstractHybrid rice has been planted throughout China to ensure food security owing to its higher yield potential than inbred rice. Meanwhile, substantial nitrogen (N) fertilizer has been applied to feed hybrid varieties for maximizing grain yield. However, to what extent the higher yield of hybrid than inbred rice depends on N fertilizer input remains unclear. A meta‐analysis was conducted in this study to (1) quantify the difference in N uptake and utilization between hybrid and inbred rice; (2) determine whether hybrid rice requires more N than inbred rice for producing per unit grain yield; and (3) evaluate the impact of the difference in crop growth duration between hybrid and inbred rice on their yield performance. The results showed that, overall, hybrid rice achieved a 10.1% higher grain yield, and 9.7% higher daily grain yield than inbred rice. This grain yield advantage increased from 6.1% to 11.9% depending on whether hybrids have longer crop growth duration than inbred rice. The yield advantage of hybrid rice was explained by higher total N uptake and internal N use efficiency, but not explained by N fertilizer input. Moreover, the yield advantage of hybrid rice with N fertilizer was driven by higher yield without N fertilizer instead of yield response to N fertilizer. These results suggest that hybrid rice does not necessarily require more N fertilizer to achieve higher yield than inbred rice. Therefore, hybrid rice could be planted with fewer external N to ensure food security and reduce environmental costs.

The agronomic performance and feasibility study of new high yield rice varieties in Tegal district

Variety is one of innovations that could contribute to the increase of rice production. The objectives of this study were to compare the agronomic performance of rice varieties and its feasibility of new high yield varieties namely Inpari 30, Inpari 32 and Inpari 33) with the existing variety (Mekongga). Research was conducted in Banjaranyar Village, Balapulang Subdistrict, Tegal Regency. The agronomic performance observed were the height of plants, number of productive tillers, length of panicles, number of grain/panicles, and yield or milled dry grain production. Meanwhile the feasibility study was calcutaed in term of Revenue Cost Ratio (R/C) analysis. Result showed the significant different in observed performance among varieties. The productivity of Inpari 30, Inpari 32 and Inpari 33 were 5.45, 5.97, and 5.89 tons/ha of milled dry grain (GKG) respectively. All new high yield varieties showed better production performance compared to Mekongga (4.96 tons/ha GKG). The feasibility study showed R/C value of Inpari 30, Inpari 32, Inpari 33 and Mekongga were 1.28, 1.41, 1.39 and 1.14, respectively. Among these varieties, Inpari 32 has the highest feasibility study value.

Optimized Supply Chain Management of Rice in South Korea: Location–Allocation Model of Rice Production

Planning for optimized farming with the aim of providing ideal site and cultivar selection is critical for a stable and sustainable supply of rice with sufficient quantity and quality to customers. In this study, a range of morphological characteristics and yield of eight rice cultivars that are commonly cultivated in Korea were investigated from 2005 to 2020. All morphological characteristics were significantly different among the eight rice cultivars. The dataset of morphological characteristics and yield was used to isolate groups of similar rice cultivars. The k-means clustering method was used to group the rice cultivars. Three groups (Group 1, Group 2, and Group 3) were created. Most cultivars were in Group 1. High-yielding rice cultivars were in Group 2, while the rice cultivars in Group 3 had the lowest rice grain yield. After grouping these rice cultivars, ideal farming locations for all three rice cultivar groups were identified to reduce transportation cost using an optimized location–allocation model. Simulation results suggested the following: (1) Group 1 should be produced in Jellanam-do (south west region), (2) Group 2 should be produced in Chungcheongnam-do (central west region), and (3) Group 3 should be mainly produced in the central west region of South Korea. Simulation results showed the potential to reduce transportation cost by around 0.014%. This can also reduce 21.04 tons of CO2 emission from a freight truck. Because these eight cultivars only make up 19.76% of the total rice production in South Korea, the cost reduction proportion was only 0.014% of total revenue. In future studies, more rice cultivars should be investigated to increase the efficiency of the model performance.

English

The study was conducted in 2017/2018 and 2018/2019 rainy seasons at Nanzolo, Domasi and Mkondezi in three replications using the RCBD following the Mother-Baby Trial Approach. The objective of the study was to evaluate grain yield of twelve high-yielding rice (Oryza sativa) varieties that were selected and shared from elite Doubled Haploid germplasms of a Collaborative Project of KAFACI (RDA) and AGRA at Suwon in Korea and Africa Rice Centre, Senegal. An improved variety called Mtupatupa was used as a common check. Data collection was done on several traits including plant height at maturity, number of effective tillers and DUS as well as VCU. The two lines SR35285-HB3469-6 and Sahel 328 met farmers&rsquo; preferences during participatory variety selection because of earliness to maturity, high grain yield, medium to slender grain shape and long to extra-long, moderate aroma and absence of the white belly on the endosperm. The Genotype &times; Environment interaction summarized by the biplot of the two principal component axes explains 96.56% of the Genetics and Genotype &times; Environmental (GGE) variation. The hierarchical clustering pattern showed two main clusters in the dendrogram description. Genotypes SR35285-HB3469-6 and Sahel 328 had been therefore released as Wachangu and Makafaci, respectively, for lowland cultivation in Malawi. Key words: Doubled Haploid, principal component analysis, DUS and VCU, GGE biplot, grain quality, grain yield, lowland, PVS.

Geographic variation in the yield formation of single-season high-yielding hybrid rice in southern China

Environmental conditions greatly affect the growth of rice. To investigate the geographic differences in yield formation of single-season high-yielding hybrid rice in southern China, experiments were conducted in 2017 and 2018 in the upper and middle–ower reaches of the Yangtze River with 10–30 main locally planted high-yielding hybrid cultivars used as materials. Compared with rice planted in the middle–lower reaches of the Yangtze River, rice planted in the upper reaches has a longer tillering duration, higher accumulated temperature (≥10°C) during tillering period, but lower accumulated temperature and solar radiation from initial booting to maturity. Yield traits comparison between the upper and the middle–lower reaches of Yangtze River showed that the former had 48.1% more panicles per unit area while the latter had 46.4% more grains per panicle; the rice yield in the former was positively correlated with the seed setting rate and the dry matter accumulation before heading, while the latter was positively correlated with grains per panicle and dry matter accumulation from booting to maturity. Comparison of the same variety Tianyouhuazhan planted in different regions showed there was a significant positive correlation between panicle number and the duration of and accumulated temperature during the tillering period (r=0.982**, r=0.993**, respectively), and between grains per panicle and accumulated solar radiation during booting period (r=0.952*). In the upper reaches of the Yangtze River, more than 90% of cultivars with an yield of greater than 11 t ha–1 had an effective panicle number of 250–340 m–2, and there was a significant negative correlation between seed setting rate and grains per panicle; therefore, the high-yielding rice production in these regions with a long effective tillering period (>40 d) should choose varieties with moderate grains per panicle, adopt crop managements such as good fertilizer and water measures during vegetative growth period to ensure a certain number of effective panicles, and to increase the dry matter accumulation before heading. While in regions with a short effective tillering period (<20 d) but good sunshine conditions during the reproductive growth period, such as the middle–lower reaches of the Yangtze River, high-yielding rice production should choose cultivars with large panicles, adopt good water and fertilizer managements during the reproductive growth period to ensure the formation of large panicles and the increase of dry matter accumulation after heading.

Incorporating Drought and Submergence Tolerance QTL in Rice (Oryza sativa L.)-The Effects under Reproductive Stage Drought and Vegetative Stage Submergence Stresses.

Drought and submergence have been the major constraint in rice production. The present study was conducted to develop high-yielding rice lines with tolerance to drought and submergence by introgressing Sub1 into a rice line with drought yield QTL (qDTY; QTL = quantitative trait loci) viz. qDTY3.1 and qDTY12.1 using marker-assisted breeding. We report here the effect of different combinations of Sub1 and qDTY on morpho-physiological, agronomical traits and yield under reproductive stage drought stress (RS) and non-stress (NS) conditions. Lines with outstanding performance in RS and NS trials were also evaluated in vegetative stage submergence stress (VS) trial to assess the tolerance level. The QTL class analysis revealed Sub1 + qDTY3.1 as the best QTL combination affecting the measured traits in RS trial followed by Sub1 + qDTY12.1. The effects of single Sub1, qDTY3.1 and qDTY12.1 were not as superior as when the QTLs are combined, suggesting the positive interaction of Sub1 and qDTY. Best performing lines selected from the RS and NS trials recorded yield advantage up to 4453.69 kg ha−1 and 6954 kg ha−1 over the parents, respectively. The lines were also found having great tolerance to submergence ranging from 80% to 100%, contributed by a lower percentage of shoot elongation and reduction of chlorophyll content after 14 days of VS. These lines could provide yield sustainability to farmers in regions impacted with drought and submergence while serving as important genetic materials for future breeding programs.