Inbred Rice Research Articles

Genetic variability analysis of partially salt tolerant local and inbred rice (Oryza sativa L.) through molecular markers

Random Amplified Polymorphic DNA (RAPD) analysis was performed to assess the genetic variability in sixteen selected germplasms of rice, Oryza sativa L. using eight decamer RAPD primers. The data obtained from this investigation reveals a high level of polymorphism between cultivars. The primers produced a total of 255 bands of which all 255 bands were polymorphic indicating 100% polymorphism. The size of the amplified bands ranged from 220 bp to 2290 bp. The number of polymorphic fragments ranged from 24 to 49 with an average of 32 polymorphic fragments for each primer. The primer OPX04 produced the maximum number (49) of polymorphic bands while the OPB04 and OPB17 produced the minimum number (24) of polymorphic bands. The polymorphic information content (PIC) values ranged from 0.6616 to 0.8845 with an average of 0.832. The highest PIC value (0.8845) was obtained for primer OPL03. The RAPD data was analyzed to determine the pair-wise genetic similarity coefficients which ranged from 0.00 to 0.83. The BRRIdhan 23 and the BRRIdhan 41 varieties were the closest genotypes with the highest similarity index of 83%. This was followed by 77% similarity between a pair of cultivars Kalamona and Horkuch. On the other hand, 100% dissimilarity was seen between BRRIdhan 53, BRRIdhan 50, BRRIdhan 10, BRRIdhan 70, BRRIdhan 54, BRRIdhan 40, BRRIdhan 23, BRRIdhan 47, BRRIdhan 41 and Dadsail respectively and between BRRIdhan 53 and Horkuch; indicating a high level of variability between paired genotypes. Cluster analysis was performed using Unweighted Paired Group of Arithmetic Means (UPGMA). The UPGMA dendrogram resolved the selected rice cultivars into four clusters.

The rice (Oryza sativa) Rc gene improves resistance to preharvest sprouting and retains seed and milled rice quality

AbstractPreharvest sprouting (PHS) remains a severe agricultural problem in rice and other crops. This study investigated the exact effect of Rc gene on PHS resistance along with seed and milled rice quality using two sets of near‐isogenic line‐derived populations, and showed the advantages of the Rc gene over other dormancy‐associated genes in protecting against PHS. Rc gene has a significant effect on PHS resistance, and Rc‐controlled dormancy does not negatively affect next agricultural production cycle. Importantly, Rc has a completely dominant maternal effect on PHS resistance, which confers an advantage to hybrid rice over inbred rice, and the effect fails to be counteracted by GA application in hybrid seed production. Moreover, Rc gene retains the same milled rice qualities of brown‐pericarp rice as that of white‐pericarp rice, and the brown‐pericarp rice possesses a higher antioxidative capacity than the white‐pericarp rice. Thus, wide application of the Rc gene would not only protect against PHS, but would also enhance the production of naturally occurring antioxidants that could make a significant contribution to human health.

English

In order to clarify whether the shift from hand-transplanting seedlings to direct seeding will bring negative effects to rice production and to find optimal nitrogen management for direct-seeded rice in Eastern China, research has been conducted in Quzhou City, in the Zhejiang Province of China in the year 2017 and 2018. One indica inbred rice variety, “Zhongjiazao-17” was planted by two different rice establishment methods (direct seeding and hand-transplantation), and five different nitrogen application rates were set as experimental treatments (0, 120 and 180 kg ha-1 in 2017 and 0, 165 and 195 kg ha-1 in 2018). The grain yield, economic profit, and rice quality were compared between direct-seeded rice and hand-transplanted rice under different nitrogen rates. Our results indicate that the direct-seeded rice showed no obvious disadvantages in grain yield compared to the hand-transplanted rice, but improved economic profit significantly. The highest grain yield and production profit were achieved at 180 kg N ha-1 in direct-seeded rice while the hand-transplanted rice achieved highest grain yield and profit at 165 kg ha-1. The direct-seeded rice showed lower physical quality but higher cooking and tasting quality than the hand-transplanted rice. Increasing the nitrogen rate improved the physical quality but decreased cooking and tasting quality in both the direct-seeded rice and hand-transplanted rice. Hence, direct-seeded rice has the potential to be promoted in Eastern China, and 180 kg ha-1 is the optimal nitrogen rate. In addition, applying sufficient nitrogen at panicle initiation is necessary to increase the grain yield of direct-seeded rice. Key words: Direct seeding, hand-transplantation, grain yield, nitrogen management, physical quality, cooking and tasting quality. &nbsp

The Analysis of Technical Efficiency of Inbred and Hybrid Lowland Rice Farming Business

The background of this research was the unachieved rice productivity of hybrid lowland rice which targeted by the Director General of Crops in 2017. Hybrid lowland rice farmers were assumed did not reach the full efficiency in the use of production factors. This study aimed to explain the general description of inbred and hybrid lowland rice farming business; analyzed the factors that influence the level of business production, and analyzed the technical efficiency and the factors that influence the technical inefficiencies of the farming business. These aims can be answered by the Stochastic Frontier Analysis (SFA) method. The data used was the raw data of the Crops Cost Structure Survey 2017 in East Java Province. This province was chosen because it was the largest production contributor of rice field in Indonesia. Harvesting area, seeds and fertilizers gave a good effect to both for inbred and hybrid lowland rice production, and for hybrid rice production were also supported by labor. The technical efficiency of inbred lowland rice production was higher (81.17 percent) compared to hybrid lowland rice production (70.49 percent). The factors that affected the technical inefficiency of inbred lowland rice were gender, education, pest control, tractors usage, counseling, and the number of labor, while factors that affected to technical inefficiency of hybrid lowland rice, education, pest control, and tractors usage.

Heterotic performance of the main yield traits in different types of Indica hybrid rice

AbstractTwo‐line hybrid rice with high efficiency and yield was successfully and widely being planted in China. HHZ is an elite inbred rice which is widely cultivated in Southern China. The latest developed engineered hybrid is promising for the future of hybrid rice breeding and production. In order to explore its heterosis performance, the main yield traits of two different groups of hybrid rice varieties and a inbred variety were investigated, specifically: (1) a large‐scale extension of high‐yield varieties of two‐line hybrid rice and their parents (restorer lines), (2) a new generation of hybrid rice created by genetic engineered with HHZ as a background genome and its parental lines, and (3) a inbred indica rice variety, HHZ. We postulate that the performance of the main yield traits of genetically engineered hybrid rice may be better than that of commercial high‐yielding hybrid rice in the same paddy field. To test our assumption, field experiments were conducted to investigate the performance of the main yield traits in the different types of hybrid rice and to compare and analyze the differences of the yield heterosis traits. The hybrid rice varieties showed obvious high‐parent heterosis for effective panicle number (EPN) per hill, grain number per panicle (GNP), seed set rate (SSR), and harvest index (HI), but high‐parent heterosis for the 1000‐grain weight (KGW) was negative. Standard heterosis for GNP and KGW was found in the hybrid rice varieties, and the standard heterosis for EPN, SSR, and HI was negative. The grain number per panicle (GNP) is the largest contributor to heterotic performance. The genetically engineered hybrid rice showed similar heterotic performance to but not greater than that of two‐line hybrid rice varieties. This study provides important insights for the breeding, cultivation, and popularization of different types of hybrid rice varieties.

Inbred varieties outperformed hybrid rice varieties under dense planting with reducing nitrogen

Field experiments were conducted over two years to evaluate the effects of planting density and nitrogen input rate on grain yield and nitrogen use efficiency (NUE) of inbred and hybrid rice varieties. A significant interaction effect was observed between nitrogen input and planting density on grain yield. Higher number of panicles per square meter and spikelets per panicle largely accounted for the observed advantage in performance of inbred, relative to hybrid varieties. Compared with high nitrogen input rate, nitrogen absorption efficiency, nitrogen recovery efficiency, and partial factor productivity increased by 24.6%, 28.0%, and 33.3% in inbred varieties, and by 32.2%, 29.3%, and 35.0% in hybrids under low nitrogen input, respectively. Inbred varieties showed higher nitrogen absorption efficiency, nitrogen recovery efficiency, and partial factor productivity than hybrids, regardless of nitrogen input level. Nitrogen correlated positively with panicle number, spikelets per panicle, biomass production at flowering, and after flowering in inbred varieties but only with panicle number and biomass production at flowering in hybrids. Inbred varieties are more suitable for high planting density at reduced nitrogen input regarding higher grain yield and NUE. These findings bear important implications for achieving high yield and high efficiency in nutrient uptake and utilization in modern rice-production systems.

Assessment of the organic-based system of rice intensification (SRI) under coastal rice field ecosystem

Objectives: The effects of different levels of organic fertilizers on the growth and yield of rice were investigated in a coastal field ecosystem under the systems of rice intensification (SRI) technology. Methods/Statistical Analysis: The study was conducted in a coastal rice field with 8.38 pH. It was laid out in a split-plot design with four treatments replicated thrice. Different amounts of organic fertilizer were applied as basal fertilizer. Data were statistically analyzed using analysis of variance (ANOVA). The significance of the treatment effect was determined using the F-test. Least significant difference (LSD) determined which means are statistically different at the 5% probability level. Findings: Results showed that the filled grains and yield increase were 35.6% and 45%, respectively, when applied with an organic fertilizer at the rate of 6 ton/ha compared with the control. Other parameters measured like the height of plants at maturity and the number of unfilled grains were all comparable with the control group. Applications: SRI technology is a potential option for growing inbred rice in coastal rice fields. Keywords: Coastal rice field; Organic-based; Rice crop; System of rice intensification

RNA-seq Reveals Differentially Expressed Genes between Two indica Inbred Rice Genotypes Associated with Drought-Yield QTLs

Two indica inbred rice lines, IR64, a drought-sensitive, and Apo, a moderately drought-tolerant genotype, were exposed to non- (control or unstressed) and water-stress treatments. Leaf samples collected at an early flowering stage were sequenced by RNA-seq. Reads generated were analyzed for differential expression (DE) implementing various models in baySeq to capture differences in genome-wide transcriptional response under contrasting water regimes. IR64, the drought-sensitive variety consistently exhibited a broader transcriptional response while Apo showed relatively modest transcriptional changes under water-stress conditions across all models implemented. Gene ontology (GO) and KEGG pathway analyses of genes revealed that IR64 showed enhancement of functions associated with signal transduction, protein binding and receptor activity. Apo uniquely showed significant enrichment of genes associated with an oxygen binding function and peroxisome pathway. In general, IR64 exhibited more extensive molecular re-programming, presumably, a highly energy-demanding route to deal with the abiotic stress. Several of these differentially expressed genes (DEGs) were found to co-localize with QTL marker regions previously identified to be associated with drought-yield response, thus, are the most promising candidate genes for further studies.

Agronomic and physiological performance of an indica–japonica rice variety with a high yield and high nitrogen use efficiency

AbstractHybrid rice (Oryza sativa L.) varieties usually need more N application to produce a higher grain yield and exhibit lower N use efficiency (NUE) than inbreds. However, little information is available about the mechanism underlying an indica–japonica rice variety with high yield and high NUE under low N rates. This study investigated this issue. The indica–japonica hybrid rice variety Yongyou 2640 (Y‐2640) and the japonica inbred rice variety Lianjing 7 (L‐7) were grown in a paddy field at N rates of 0 and 200 kg N ha−1. The results showed that the grain yield and internal NUE (grain yield/total N uptake of plants) of Y‐2640 were 16–23% and 9–10%, respectively, higher than those of L‐7. A higher grain yield for Y‐2640 was mainly attributed to the greater spikelet number per unit area that resulted from greater root oxidation activity at panicle initiation and its higher crop growth rate and net assimilation rate before heading. A higher leaf area index and greater root length, root, and shoot biomass were the important agronomic traits of Y‐2640. Higher cytokinin content and the expression of genes involved in the amino acid transporters OsAAP1 and OsLHT1 in the roots and leaves, a higher photosynthetic NUE, and a greater N harvest index were the main physiological traits of Y‐2640. The results suggest that improved agronomic and physiological performance accounts for the high yield and high NUE for the indica–japonica hybrid rice variety.

Genetic Diversity Analysis of Hybrid Rice Parental Lines and Genetic Purity Assessment of Hybrid Seeds of China

Thirty-five pairs of SSR primers were used for genetic diversity analysis and DNA fingerprinting of 31 hybrid rice core parental lines developed in central- and southern-China using one japonica rice line and three inbred rice lines as the check varieties. The average number of alleles (Na) per SSR locus was 4.02, with a range of two to eight, the effective number of alleles (Ne) was 83.16 with a mean of 2.38, ranging from 1.19 to 4.66. The polymorphic information content (PIC) ranged from 0.16 to 0.79, with an average number of 0.52. The results of the cluster analysis indicated that the check varieties viz., one japonica rice and three inbred rice, were clustered into two groups with similarity coefficients of 0.62 and 0.71 respectively indicating their relatedness. Thirty-one hybrid rice parental lines were clustered into 6 groups according to their different types, pedigrees and regions of development with similarity coefficients of approximately 0.76. The highest genetic similarity coefficient (0.94) was observed between Y58S and C815S, and the lowest (0.63) was observed between Quan9311A and Peiai64S. The purity of one hybrid rice cultivar was tested using characteristic marker and the field test, and it was demonstrated that the purities obtained using the two methods were similar. This research will be helpful for rice breeding, new cultivar registration and seed production.

Performance and Energy Efficiency of New Rice Varieties Under Aerobic Growing Conditions, Different Tillage and Direct Seeding Methods in Kalinga, Philippines

Objectives: To evaluate the performance of three (3) selected hybrid rice varieties, namely NSIC RC9 (V1), M19 (V2), M20 (V3) and one (1) inbred rice variety (M228) through minimum and conventional tillage with the use of different direct-seeding methods for seeding in aerobic condition in Kalinga, Philippines. Methods/analysis: The field experiment was laid out in a split-split-plot in RCBD with tillage, seeding method, and variety as treatments in four replications. The agronomic performance, yield performance, and energy efficiency of the rice varieties were evaluated in two cropping year from August 2013 to March 2015. Agronomic performance, such as seed emergence, height at maturity, number of productive tillers, length of panicles, percent of filled grains, weight of 1000 seeds, final grain yield of the said varieties were analyzed for each treatments. The cost effectiveness, labor productivity, and energy efficiency were also analyzed for each treatment. Findings: Generally, there are no significant differences of the selected varieties including the inbred variety in terms of seed emergence, plant height, length of panicle, productive tillers, and percent filled grains, 1000 grain weight and grain yield under tillage practices and different seeding techniques. In like manner, the agronomic and yield performance varied across varieties. Regardless of tillage practices, the varieties did not exhibit any significant differences in terms of production cost, labor productivity and energy efficiency after two cropping year. Furthermore, plastic drum seeding techniques found to be more cost effective, while Korean seeding technique had the highest labor productivity and most energy efficient. Based on the result of the study, the agronomic and yield performance of newly released varieties are comparable as to inbred varieties used while the used of plastic drum seeder had the lowest cost of production and highest overall energy ratio (OER). On the other hand, the highest labor productivity was observed from the used of Korean seeder. Novelty/improvement: This study demonstrated that selected rice varieties exhibited the same agronomic performance and yield performance under conservation and minimum tillage with different seeding techniques in Kalinga, Philippines. In addition, the production cost, labor productivity, and energy efficiency depend from seeding techniques to be employed. Keywords: Energy Efficiency, Aerobic, Tillage, Direct Seeding, Labor Productivity.

Higher leaf area through leaf width and lower leaf angle were the primary morphological traits for yield advantage of japonica/indica hybrids

The yield potential of japonica/indica hybrids (JIH) has been achieved over 13.5 t ha−1 in large-scale rice fields, and some physiological traits for yield advantage of JIH over japonica inbred rice (JI) and indica hybrid rice (IH) were also identified. To date, little attention has been paid to morphological traits for yield advantage of JIH over JI and IH. For this reason, three JIH, three JI, and three IH were field-grown at East China (Ningbo, Zhejiang Province) in 2015 and 2016. Compared with JI and IH, JIH had 14.3 and 20.8% higher grain yield, respectively, attributed to its more spikelets per panicle and relatively high percentage of filled grains. The advantage in spikelets per panicle of JIH over JI and IH was shown in number of grains on the upper, middle, and lower branches. Compared with JI and IH, JIH had higher leaf area through leaf width and lower leaf angle of upper three leaves, higher leaf area index and leaf area per tiller at heading and maturity stages, higher stem weight per tiller and K and Si concentrations of stem at maturity, higher dry matter weight in leaf, stem, and panicle at heading and maturity stages, and higher biomass accumulation after heading and lower biomass translocation from stem during ripening. Leaf width of upper three leaves were correlated positively, while leaf angle of upper three leaves were correlated negatively with biomass accumulation after heading, stem weight per tiller, and per unit length. Our results indicated that the grain yield advantage of JIH was ascribed mainly to the more spikelets per panicle and relatively high percentage of filled grains. Higher leaf area through leaf width and more erect leaves were associated with improved biomass accumulation and stem weighing during ripening, and were the primary morphological traits underlying higher grain yield of JIH.

EVALUATE SOME NEW INBRED RICE AND MALE STERILE VARIETIES UNDER DUS AND VCU EXPERIMENTS

The main objective of study are evaluated some new inbred rice and male sterile varieties under Distinct, Uniform and Stability (DUS) and Value of Cultivated and Used (VCU) Experiments. A number of seven rice varieties were used, Sakha 101, Sakha 102, Sakha 104, Giza 177, Giza 178, Giza 182 and Egyptian yasmine; moreover, GZ 10154 and GZ 8564-Sp 70, as well as EGMS and CMS1 as promising lines to evaluating by DUS and VCU. The data were recorded on morphological and yield characters. The results could be concluded that: regarding to qualitative characteristics (PQ and QL), from 24 PQ and QL characters, the nine rice varieties recorded the same score for 19 characters; moreover, the rice varieties Egyptian jasmine was dissimilar in the score No. 24, 39, and 60, that referred to this variety belong to Indica type, while the rice varieties Sakha 101 and Giza 178 were similar only in score no.11, which belong to Japonica and Indica japonica types, that meaning these varieties were highly uniform and stability in qualitative characters than the other promising line GZ 10154. Regarding to quantities characteristics (QN), from 27 QN characters, nine rice varieties recorded the same score for 20 characters; moreover, the rice varieties Sakha 101, Sakha 102, Sakha 104, Giza 177, Giza 178, Giza 182, Egyptian yasmine and GZ 8564-Sp70 were similar in the score no. 1, 12, 23, 48, 49 and 50, while the promising line GZ 10154 was dissimilar in these scores during the two seasons, meaning that all these varieties were highly uniform and stability than the other promising, line GZ 10154. These results were conformed to VCU results, where the studied varieties recorded the highest grain yield/day. From these results could be concluded that all the varieties, except GZ 10154, accepted as a new rice release variety, but the promising line GZ 10154 required to more recurrent selection to increase their uniform, as well as CMS line was accepted could be evaluated under different conditions, but EGMS should be evaluated under heat stress conditions.

EVALUATE SOME NEW INBRED RICE AND MALE STERILE VARIETIES UNDER DUS AND VCU EXPERIMENTS

The main objective of study is evaluated some new inbred rice and male sterile varieties under Distinct, Uniform and Stability (DUS) and Value of Cultivated and Used (VCU) Experiments. A number of seven rice varieties were used, Sakha 101, Sakha 102, Sakha 104, Giza 177, Giza 178, Giza182 and Egyptian Yasmine; moreover, GZ. 10154 and GZ 8564-Sp 70, as well as EGMS and CMS1 as promising lines to evaluating by DUS and VCU. The data were recorded on morphological and yield characters. The results could be concluded that: regarding to qualitative characteristics (PQ and QL), from 24 PQ and QL characters, the nine rice varieties recorded the same score for 19 characters; moreover, the rice varieties Egyptian jasmine was dissimilar in the score No. 24, 39, and 60, that referred to this variety belong to Indica type while the rice varieties Sakha 101and Giza 178 were similar only in score no.11, which belong to Japonica and Indica japonica types, that meaning these varieties were highly uniform and stability in qualitative characters than the other promising line GZ10154. Regarding to quantities characteristics (QN), from 27 QN characters, 9 rice varieties recorded the same score for 20 characters; moreover, the rice varieties Sakha 101, Sakha 102, Sakha 104, Giza 177, Giza 178, Giza 182, Egyptian yasmine and GZ 8564-Sp70 were similar in the score no. 1, 12, 23, 48, 49 and 50, while the promising line GZ 10154 was dissimilar in these scores during the two seasons, meaning that all these varieties were highly uniform and stability than the other promising, line GZ 10154. These results were conformed to VCU results, where the studied varieties recorded the highest grain yield/day. From these results could be concluded that all the varieties, except GZ 10154, accepted as a new rice release variety, but the promising line GZ 10154 required to more recurrent selection to increase their uniform, as well as CMS line was accepted could be evaluated under different conditions, but EGMS should be evaluated under heat stress conditions.

Seasonal changes in crop growth and grain yield of different japonica rice cultivars in southeast China

AbstractIt is unknown whether japonica rice bred up in the single season is suitable for growing in the late season in southeastern China. To evaluate the response of grain yield and growth traits of japonica varieties to the changing growing season, two types of japonica rice (inbred japonica and indica‐japonica hybrid rice) were planted during single and late seasons in 2016 and 2017. The grain yields of indica‐japonica hybrid rice were 8.3–9.5 t ha−1 and 9.2–10.8 t ha−1 in the late and single season, respectively, which were significantly greater than those of japonica inbred rice. In addition, the grain yields decreased when the growing season was switched from the single to the late season, being 17.3–23.7% for the inbred japonica rice and 4.0–9.7% for the indica‐japonica hybrid rice, indicating a small yield gap between the single and late season of the indica‐japonica hybrid rice. Furthermore, the indica‐japonica hybrid rice had a higher accumulated biomass, leaf area index (LAI), and spikelets per panicle; comparable phenological traits and leaf photosynthetic rate during panicle development; but lower grain weight and grain filling percentage compared with those of the inbred japonica rice. These results suggested that high grain yield of the indica‐japonica hybrid rice during the late season might be attributed to the high accumulation of biomass and the large panicle size. Thereby, we suggested that the great LAI during panicle development, high biomass accumulation before heading, and large panicle size might be useful as indicators for breeding the japonica variety during the late season.

Genotypic Differences and Nitrogen Uptake of Lowland Rice (Oryza sativa L.) under Two Production Systems and N Application

Climate change has been causing low yield in rice production. In order to counter the negative effects of climate change in rice production, it is important to choose a suitable variety and production system, as well as application of nitrogen. This study sought to determine the agronomic and yield performance of inbred and hybrid rice under System of Rice Intensification (SRI) and conventional production systems, as well as evaluate the Nitrogen Use Efficiency (NUE) of these varieties under two production systems and N application. The experiment was laid out in a nested design in RCBD with varieties as the main plot and N application as subplot -1 -1 (0 kg N ha and 90 kg N ha ) under two production systems. Inbred rice grown under SRI headed earlier than hybrid rice in similar condition and both varieties in the conventional production system. Irrespective of production system, hybrid variety and those applied with N were taller than inbred without N application. Regardless of the variety and levels of N applied, lowland rice grown under SRI produced the most productive tillers, heaviest1,000 grains, heaviest root pulling resistance (RPR), and highest leaf area index(LAI). In terms of N levels, grain yield was higher when 90 kg of N was applied in both production systems than without N. Both varieties had -1 comparable grain yield when applied with 90 kg N ha . Highest NUE was obtained -1 under SRI with application of 90 kg N ha and under conventional system without N application. Thus, rice grown under SRI had better utilization of applied N. Meanwhile, water supplied in SRI was reduced by 32% compared to the conventional production system.

Hybrid rice produces a higher yield and emits less methane

Hybrid rice has a higher yield potential than inbred rice, but the difference in CH<sub>4</sub> emissions between the two groups is still unclear, particularly regarding straw incorporation. In the present study, a pot experiment was conducted to examine the difference in CH<sub>4</sub> emissions between inbred (Huanghuazhan) (IR) and hybrid (Rongyouhuazhan) (HR) rice cultivars, both with or without straw incorporation in subtropical China. The results showed that HR produced both greater grain yield and biomass than IR. In contrast, when compared with IR, HR reduced the cumulative CH<sub>4</sub> emissions by an average of 18.6%. No significant interactions between rice cultivars and straw management on yield or CH<sub>4</sub> emissions were found. HR significantly increased the abundance of methanogens and methanotrophs by 38.9% and 93.4% relative to IR, respectively, thereby reducing CH<sub>4</sub> concentrations in the soil pore water. Therefore, we suggest that cultivar rice can produce a higher yield and better mitigate CH<sub>4</sub> emissions when compared to inbred rice, regardless of the use of straw incorporation.

Basal internode elongation of rice as affected by light intensity and leaf area

Short basal internodes are important for lodging resistance of rice (Oryza sativa L.). Several canopy indices affect the elongation of basal internodes, but uncertainty as to the key factors determining elongation of basal internodes persists. The objectives of this study were (1) to identify key factors affecting the elongation of basal internodes and (2) to establish a quantitative relationship between basal internode length and canopy indices. An inbred rice cultivar, Yinjingruanzhan, was grown in two split-plot field experiments with three N rates (0, 75, and 150 kg N ha−1 in early season and 0, 90, and 180 kg N ha−1 in late season) as main plots, three seedling densities (16.7, 75.0, and 187.5 seedlings m−2) as subplots, and three replications in the 2015 early and late seasons in Guangzhou, China. Light intensity at base of canopy (Lb), light quality as determined from red/far-red light ratio (R/FR), light transmission ratio (LTR), leaf area index (LAI), leaf N concentration (NLV) and final length of second internode (counted from soil surface upward) (FIL) were recorded. Higher N rate and seedling density resulted in significantly longer FIL. FIL was negatively correlated with Lb, LTR, and R/FR (P < 0.01) and positively correlated with LAI (P < 0.01), but not correlated with NLV (P > 0.05). Stepwise linear regression analysis showed that FIL was strongly associated with Lb and LAI (R2 = 0.82). Heavy N application to pot-grown rice at the beginning of first internode elongation did not change FIL. We conclude that FIL is determined mainly by Lb and LAI at jointing stage. NLV has no direct effect on the elongation of basal internodes. N application indirectly affects FIL by changing LAI and light conditions in the rice canopy. Reducing LAI and improving canopy light transmission at jointing stage can shorten the basal internodes and increase the lodging resistance of rice.

Dissecting a heterotic gene through GradedPool-Seq mapping informs a rice-improvement strategy

Hybrid rice breeding for exploiting hybrid vigor, heterosis, has greatly increased grain yield. However, the heterosis-related genes associated with rice grain production remain largely unknown, partly because comprehensive mapping of heterosis-related traits is still labor-intensive and time-consuming. Here, we present a quantitative trait locus (QTL) mapping method, GradedPool-Seq, for rapidly mapping QTLs by whole-genome sequencing of graded-pool samples from F2 progeny via bulked-segregant analysis. We implement this method and map-based cloning to dissect the heterotic QTL GW3p6 from the female line. We then generate the near isogenic line NIL-FH676::GW3p6 by introgressing the GW3p6 allele from the female line Guangzhan63-4S into the male inbred line Fuhui676. The NIL-FH676::GW3p6 exhibits grain yield highly increased compared to Fuhui676. This study demonstrates that it may be possible to achieve a high level of grain production in inbred rice lines without the need to construct hybrids.

Limited yield advantage of early-season rice hybrids over inbreds in middle-lower reaches of the Yangtze River

Early-season rice plays a significant role in double rice-cropping system in China to improve the grain yield per unit of area. But recently, the stagnation of grain yield increase has been witnessed for early-season rice varieties in middle-lower reaches of the Yangtze River, particular in the national rice regional adaption trials of southern China. Further, in the early cropping season, hybrid rice did not always perform better than inbred rice in grain production. It is relevant to question whether yield ceilings have been reached in early-season indica rice before a new breakthrough on the germplasm exploitation. Field experiments were conducted to evaluate the yield performance of five inbreds and their 12 derived hybrid rice varieties in 2017 and 2018 in Hangzhou, China. Limited yield advantage of early-season hybrids over inbreds was observed, commonly less than 5.00% and averaged as 0.62% in 2017 and 3.20% in 2018. The hybrids always produced more panicles per plant but less grains per panicle with similar growing periods compared with the inbreds. Then, the genetic distance of the hybrid parents was surveyed using 48 selected molecular markers, showing low polymorphisms. Further, they were genotyped for four critical quantitative trait loci for both yield traits and heading date and three ones only for yield traits. So did 60 major early-season indica rice varieties at the four pleiotropic loci. Evidence was shown for the high uniform of their haplotype combinations across the tested materials, which could lead to early heading and low yield potential. Our work revealed the low genetic diversity, or called genetic bottleneck, for early-season hybrids to further improve grain yield potential. Moreover, along with the popularization of low-input requirements, the inbred rice varieties of cheap seed price might be a more suitable alternative for this cropping season in middle-lower reaches of the Yangtze River.