Components Of Grain Yield Research Articles

Screening of barley genotypes for drought tolerance based on culm reserves contribution to grain yield

Grain filling determines the grain weight, a major component of grain yield in cereals. Grain filling in barley depends on current assimilation and culm reserves. A pot experiment was conducted at the Grilled House, Department of Crop Botany, Bangladesh Agricultural University, Mymensingh during October 2015–May 2016 to study the grain filling patterns and the contributions of culm reserves to grain yield under drought stress. The experiment consisted of two factors—barley cultivars (six cultivars) and drought stress treatments (control and drought stress). Drought stress was imposed by limiting the irrigation during grain filling period. The tillers were sampled at anthesis, milk-ripe and maturity to determine the changes in dry weights of different parts, viz., leaf lamina, culm with sheath, spikes, and grains; and to examine the contribution of culm reserves to grain yield. The result in this experiment revealed that the grain yield was reduced by 5–25% due to drought stress. The reduction in grain yield was attributable to reduce number of grains per spike and lighter grain weight due to the stress. Drought stress drastically reduced the grain filling duration by about 30% and the stress induced early leaf senescence. Photosynthesis rate and leaf greenness were also reduced in stress. The stress altered the contribution of culm reserves, water soluble carbohydrates (WSCs) in culms to grains. At milk ripe stage, accumulation reached its peak. It accumulated 29.0 to 70.0 mg and from 15.8 to 40.6 mg culm−1 in control and stressed plants, respectively. The residual culm WSCs ranged from 3.5 to 11.2 mg and 1.0 to 3.5 mg culm−1 under control and stress conditions, respectively. The highest contribution of culm WSCs to grain yield was observed in BARI barley2 and the lowest was in BARI barley5 both in control and stress condition. Among the cultivars studied, BARI barley2 produced higher yield with the higher contribution of culm reserves to grain yield under the drought stress.J. Bangladesh Agril. Univ. 16(1): 62-66, April 2018

Zebularine treatment is associated with deletion of FT-B1 leading to an increase in spikelet number in bread wheat.

The number of rachis nodes (spikelets) on a wheat spike is a component of grain yield that correlates with flowering time. The genetic basis regulating flowering in cereals is well understood, but there are reports that flowering time can be modified at a high frequency by selective breeding, suggesting that it may be regulated by both epigenetic and genetic mechanisms. We investigated the role of DNA methylation in regulating spikelet number and flowering time by treating a semi-spring wheat with the demethylating agent, Zebularine. Three lines with a heritable increase in spikelet number were identified. The molecular basis for increased spikelet number was not determined in 2 lines, but the phenotype showed non-Mendelian inheritance, suggesting that it could have an epigenetic basis. In the remaining line, the increased spikelet phenotype behaved as a Mendelian recessive trait and late flowering was associated with a deletion encompassing the floral promoter, FT-B1. Deletion of FT-B1 delayed the transition to reproductive growth, extended the duration of spike development, and increased spikelet number under different temperature regimes and photoperiod. Transiently disrupting DNA methylation can generate novel flowering behaviour in wheat, but these changes may not be sufficiently stable for use in breeding programs.

Analysis of contributors to grain yield in wheat at the individual quantitative trait locus level

AbstractIn wheat, strong genetic correlations have been found between grain yield (GY) and tiller number per plant (TN), fertile spikelet number per spike (FSN), kernel number per spike (KN) and thousand‐kernel weight (TKW). To investigate their genetic relationships at the individual quantitative trait locus (QTL) level, we performed both normal and multivariate conditional QTL analysis based on two recombinant inbred lines (RILs) populations. A total of 79 and 48 normal QTLs were identified in the International Triticeae Mapping Initiative (ITMI)/SHW‐L1 × Chuanmai 32 (SC) populations, respectively, as well as 55 and 35 conditional QTLs. Thirty‐two QTL clusters in the ITMI population and 18 QTL clusters in the SC population explained 0.9%–46.2% of phenotypic variance for two to eight traits. A comparison between the normal and conditional QTL mapping analyses indicated that FSN made the smallest contribution to GY among the four GY components that were considered at the QTL level. The effects of TN, KN and TKW on GY were stronger at the QTL level.

Grain filling patterns of barley as affected by high temperature stress

Grain filling determines the grain weight, a major component of grain yield in cereals. Grain filling in barley depends on current assimilation and culm reserves (mainly water-soluble carbohydrates). Nowadays barley is facing heat stress problem which is mostly responsible to reduce the yield of barley. A field experiment was conducted at the Field Lab, Department of Crop Botany, BangladeshAgriculturalUniversity, Mymensingh during November 2015 to March 2016 to study the grain filling patterns and the contributions of culm reserves to grain yield under heat stress. The experiment consisted of two factors—barley cultivars and heat stress. The heat stress was imposed by late sowing. The tillers were sampled once a week during grain filling period to determine the changes in dry weights of different parts, viz., leaves, culm with sheath, spikes, and grains; and to examine the contribution of culm reserves to grain yield. The results in the experiment revealed that the grain yield was reduced by 22-28% due to the stress. The grain yield varied from 52 to 150 g m−2 with the mean of 102 g m−2 under control while it varied from 37 to 116 g m−2 with the mean of 75 g m−2 under heat stress. Among the cultivars studied BARI Barley5, BARI Barley2 and BARI Barley1, seemed as high yielders while BARI Barley3, BARI Barley4, BARI Barley6 as the low yielders under heat stress treatment. The reduction in grain yield was attributable mainly to lighter grain weight due to the stress. Heat stress drastically reduced the grain filling duration by 45–50%. However, the stress increased the grain filling rate by 6–53%. The amount of reserves remobilized to grain varied among the cultivars ranging from 4.8 to 12.77 mg spike−1 in control and from 1.73 to 6.25 mg spike−1 in stressed plants. The stressed barley plants exhibited lower accumulation of reserves in culm but they showed almost its complete remobilization to the grain. The contribution of culm reserves to grain yield varied from 1.13 to 19.52%, and 1.09 to 2.11% in control and in stressed plants, respectively. In conclusion, culm reserve is the important attributes in grain yield in Bangladeshi barley cultivars but the contribution remains almost unaffected due the post-anthesis heat stress.J. Bangladesh Agril. Univ. 15(2): 174-181, December 2017

Associação de herbicidas para o controle de plantas daninhas em feijão do tipo preto

O feijão do tipo preto é um dos principais grãos cultivados no Brasil, com importância econômica, social e cultural. As perdas de produtividade de grãos, por competição com as plantas daninhas, em especial Digitaria ciliaris (milhã/capim-colchão) e Urochloa plantaginea (capim marmelada/papuã) podem chegar a níveis de até 80% caso nem um método de controle for adotado. Buscando o controle dessas plantas daninhas, objetivou-se com o trabalho avaliar a eficácia e a seletividade de herbicidas aplicados em pré e pós-emergência do feijão do tipo preto. O delineamento experimental utilizado foi de blocos casualizados, com quatro repetições. Os herbicidas utilizados foram: fomesafen (250 g ha-1 de i.a), s-metolachlor (1200 g ha-1 de i.a), oxifluorfen (480 g ha-1 de i.a), clomazone (1000 g ha-1 de i.a), pendimentalin (1000 g ha-1 de i.a), flumioxazin (25 g ha-1 de i.a), fluazifop-p-buthyl (250 g ha-1 de i.a), imazamox (42 g ha-1 de i.a), bentazon (720 g ha-1 de i.a), bentazon + imazamox (600 + 28 g ha-1 de i.a), fluazifop-p-buthyl + fomesafen (250 +250 g ha-1 de i.a), seguidos de mais duas testemunhas, uma capinada e outra infestada. O oxifluorfen apresentou os maiores níveis de fitotoxicidade ao feijoeiro cultivar BRS Campeiro, o que resultou no efeito negativo sobre os componentes do rendimento de grãos, juntamente com a testemunha infestada, o s-metolachlor, o pendimentalin, o flumioxazin, o fomesafen e o bentazon. A mistura comercial composta de bentazon + imazamox apresentou baixa fitotoxicidade, os melhores resultados em relação aos componentes do rendimento de grãos, aliado a um bom controle da milhã e do papuã.

Does the pre-flowering period determine the potential grain weight of sunflower?

Grain weight (GW) is an important component of grain yield and quality of sunflower and the improvement of this trait has been proposed as an aim for breeding of this crop. There is strong evidence suggesting the pre-flowering period as key to determining GW in different crops; however, the key traits and mechanisms controlling GW during this phase are still largely unknown in sunflower. This study conducted a detailed survey of how the pre-flowering period determines grain growth dynamics by assessing the early developmental process during the growth of reproductive organs and the sensitivity of GW, grain number (GN) and grain oil concentration to different source–sink manipulations immediately before flowering. Two experiments were carried out under field conditions in two growing seasons. In Exp. 1 two sunflower oilseed hybrids contrasting in GW (Alybro and SG) were sown at the Experimental Station of the Universidad Austral de Chile in Valdivia (39°47′S, 73°14′W), Chile. In Exp. 2, the same hybrids plus a confectionery genotype (RHA) were evaluated in the Experimental Station where two source–sink treatments were performed: a control (without manipulation) and a shading treatment starting 16days previous to anthesis, i.e. during the R2-R5 period. Crop development, average and individual GW, GN and oil concentration of grains were assessed at harvest. Also, flower and grain traits and their dynamics were measured from early reproductive stage (ovary at R3) to harvest in different grain positions from the capitulum (e.g., fresh and dry weight and dimensions of grains, pericarp and embryo and grain oil concentration). GW was significantly affected by genotype and shading treatments imposed at pre-anthesis, but no statistical effect of the lower source–sink ratio was found on GN. Contrary to GW, grain oil of oilseed genotypes was highly conservative under the source–sink reduction in our study. Positive associations were found between final GW and: ovary weight at R3, at anthesis (R5), ovary growth rate, grain dimensions and water content. Final GW also showed a linear association with ovary growth rate. This study is the first to evaluate the ovary weight from the early development stage and the ovary growth rate during the pre-anthesis period in sunflower and the effect of source reduction at pre-anthesis on grain oil concentration, supporting the importance of the maternal tissues on the setting of potential and actual GW in sunflower.

Influence of the Russian wheat aphid Diuraphis noxia (Kurdjumov) (Homoptera, Aphididae) on productive qualities of spring bread wheat and barley grown from the seeds from aphid-infested spikes

The aftereffects of the Russian wheat aphid (RWA) Diuraphis noxia on sowing and productive qualities of barley and spring bread wheat grain were assessed. Seeds of 4 cultivars of barley (Volgar, Povolzhsky 65, Kazak, and Povolzhsky 16) and 4 cultivars of spring wheat (Kinelskaya 59, Kinelskaya Otrada, Kinelskaya Niva, and Kinelskaya 2010) from spikes infested and uninfested with RWA in 2007 and in 2014 were sown in the subsequent years, using 0.5 m2 experimental plots in four replications, at a seeding rate of 300 grains/m2. The least significant difference (LSD0.5) was used to compare the mean ± standard deviation (SD) values. The field germination rate of seeds from spring wheat spikes damaged by RWA was reduced by 15%. Of the components of grain yield, barley and spring wheat grown from seeds from the infested spikes showed a 23-31% smaller number of productive tillers before harvesting, a 16% smaller number of grains per spike, a 13-16% lower grain weight per spike, and a total yield loss of 33-42%. In hulless bread wheat RWA fed on the developing kernels inflicting greater damage, whereas the hulled barley seeds were practically not damaged. The mean yield loss of the barley and spring wheat spikes infested with RWA was 24-32% and 50-66%, respectively. Due to the greater tillering capacity and formation of secondary productive tillers in barley, about 52% of the productive barley tillers and 37-39% of spring wheat ones were infested with RWA, which resulted in a comparable yield loss (20-25% in barley and 19-23% in spring wheat). Resistance to RWA was higher in spring wheat and barley cultivars with a shorter vegetation period, looser spikes, and thinner culm walls. The length of productive tillers damaged by RWA was reduced by 21-28%, which determined a lower incidence of leaf diseases.

Quantitative Trait Loci Mapping for Spike Characteristics in Hexaploid Wheat.

Wheat ( L.) spike characteristics determine the number of grains produced on each spike and constitute key components of grain yield. Understanding of the genetic basis of spike characteristics in wheat, however, is limited. In this study, genotyping-by-sequencing (GBS) and the iSelect 9K assay were used on a doubled-haploid (DH) soft red winter wheat population that showed a wide range of phenotypic variation for spike traits. A genetic map spanning 2934.1 cM with an average interval length of 3.4 cM was constructed. Quantitative trait loci (QTL) analysis involving additive effects, epistasis (QQ) and QTL × environment (QE), and epistasis × environment (QQE) interactions detected a total of 109 QTL, 13 QE, and 20 QQ interactions in five environments. Spike characteristics were mainly determined by additive effects and were fine-tuned by QQ, QE, and QQE. Major QTL / explained up to 30.9% of the phenotypic variation for spike length (SL) and fertile spikelet number, .1 explained up to 15.6% of the phenotypic variation of grain number per spikelet, and explained up to 80.2% of the phenotypic variation for spike compactness. Additionally, QTL for correlated spike characteristics formed QTL clusters on chromosomes 1A, 5A, 2B, 3B, 5B, 1D, and 5D. This study expands the understanding of the genetic basis of spike characteristics in hexaploid wheat. A number of stable QTL detected in this study have potential to be used in marker-assisted selection. Additionally, the genetic map generated in this study could be used to study other traits of economic importance.

A single-nucleotide polymorphism causes smaller grain size and loss of seed shattering during African rice domestication.

Grain size is one of the most important components of grain yield and selecting large seeds has been a main target during plant domestication. Surprisingly, the grain of African cultivated rice (Oryza glaberrima Steud.) typically is smaller than that of its progenitor, Oryza barthii. Here we report the cloning and characterization of a quantitative trait locus, GL4, controlling the grain length on chromosome 4 in African rice, which regulates longitudinal cell elongation of the outer and inner glumes. Interestingly, GL4 also controls the seed shattering phenotype like its orthologue SH4 gene in Asian rice. Our data show that a single-nucleotide polymorphism (SNP) mutation in the GL4 gene resulted in a premature stop codon and led to small seeds and loss of seed shattering during African rice domestication. These results provide new insights into diverse domestication practices in African rice, and also pave the way for enhancing crop yield to meeting the challenge of cereal demand in West Africa.

Analysis of the genetic architecture of maize ear and grain morphological traits by combined linkage and association mapping.

Using combined linkage and association mapping, 26 stable QTL and six stable SNPs were detected across multiple environments for eight ear and grain morphological traits in maize. One QTL, PKS2, might play an important role in maize yield improvement. In the present study, one bi-parental population and an association panel were used to identify quantitative trait loci (QTL) for eight ear and grain morphological traits. A total of 108 QTL related to these traits were detected across four environments using an ultra-high density bin map constructed using recombinant inbred lines (RILs) derived from a cross between Ye478 and Qi319, and 26 QTL were identified in more than two environments. Furthermore, 64 single nucleotide polymorphisms (SNPs) were found to be significantly associated with the eight ear and grain morphological traits (-log10(P) > 4) in an association panel of 240 maize inbred lines. Combining the two mapping populations, a total of 17 pleiotropic QTL/SNPs (pQTL/SNPs) were associated with various traits across multiple environments. PKS2, a stable locus influencing kernel shape identified on chromosome 2 in a genome-wide association study (GWAS), was within the QTL confidence interval defined by the RILs. The candidate region harbored a short 13-Kb LD block encompassing four SNPs (SYN11386, PHM14783.16, SYN11392, and SYN11378). In the association panel, 13 lines derived from the hybrid PI78599 possessed the same allele as Qi319 at the PHM14783.16 (GG) locus, with an average value of 0.21 for KS, significantly lower than that of the 34 lines derived from Ye478 that carried a different allele (0.25, P < 0.05). Therefore, further fine mapping of PKS2 will provide valuable information for understanding the genetic components of grain yield and improving molecular marker-assisted selection (MAS) in maize.

Grain Yield Differences of Soybean Cultivars Due to Solar Radiation Interception

Soybean [Glycine max (L.) Merr.] growth rate and grain yield are modified by the interception and solar radiation use efficiency. Thus, it is desirable that the most of plant photosynthetic structures intercepting solar radiation in order to have increment in carbon fixation and reflection on growth and yield. The goal of this study was to assess if soybean cultivars differ in grain yield in relation to solar radiation interception. Four soybean cultivars were evaluated at stages V6, V9, R2, R4, R6 and R8. To determine the photosynthetically active radiation interception by the canopy, the plants were divided into two parts (upper and lower strata). For grain yield components, the plants were divided into three parts (upper, middle and lower thirds). Of the photosynthetically active radiation intercepted by the vegetative canopy at the reproductive stages, the maximum observed intercept was 5.2% in the lower stratum of the plants. The number of infertile nodes increased in the lower third of plants due to low interception of solar radiation in this plant region. Thus, the soybean cultivars more efficient in intercepting photosynthetically active radiation inside the vegetative canopy showed higher grain yields.

Association between Grain Size and Shape and Quality Traits, and Path Analysis of Thousand Grain Weight in Iranian Bread Wheat Landraces from Different Geographic Regions

Grain characteristics, particularly grain weight, grain morphology, and grain protein content (GPC), are important components of grain yield and quality in wheat. A set of 98 bread wheat landraces from different geographic regions of Iran were used across 2013-2014 and 2014-2015 to determine the phenotypic diversity and relations between thousand grain weight (TGW), grain morphology and grain quality. A high-throughput method was used to capture grain size and shape. The genotypes were significantly different (P &lt; 0.001) for all traits which reflects the high levels of diversity. A moderate to high broad sense heritability was found for all traits and ranged between 0.68 and 0.95 for grain yield and factor from density (FFD), respectively. Significant positive correlations were observed between TGW and grain size (or shape) exception of aspect ratio (AR) and roundness. However, grain quality traits, especially GPC had significant negative correlation with TGW. Based on stepwise regression analysis by taking TGW as dependent variable, grain volume, FFD, width, perimeter and Hardness Index (HI) were recognized as the most important traits and explained more than 99.3% of total variation of TGW. The path analysis revealed that FFD has maximum direct effect on TGW followed by volume, whereas perimeter and width had relatively less direct effect on TGW. According to cluster analysis, landraces separated into 5 clusters, and cluster III and IV had the maximum and minimum average for the most traits, respectively. Our study provides new knowledge on the relations between TGW, grain morphology and grain quality in bread wheat, which may aid the improvement of wheat grain weight trait in further research.

Association between Grain Size and Shape and Quality Traits, and Path Analysis of Thousand Grain Weight in Iranian Bread Wheat Landraces from Different Geographic Regions

Grain characteristics, particularly grain weight, grain morphology, and grain protein content (GPC), are important components of grain yield and quality in wheat. A set of 98 bread wheat landraces from different geographic regions of Iran were used across 2013-2014 and 2014-2015 to determine the phenotypic diversity and relations between thousand grain weight (TGW), grain morphology and grain quality. A high-throughput method was used to capture grain size and shape. The genotypes were significantly different (P &lt; 0.001) for all traits which reflects the high levels of diversity. A moderate to high broad sense heritability was found for all traits and ranged between 0.68 and 0.95 for grain yield and factor from density (FFD), respectively. Significant positive correlations were observed between TGW and grain size (or shape) exception of aspect ratio (AR) and roundness. However, grain quality traits, especially GPC had significant negative correlation with TGW. Based on stepwise regression analysis by taking TGW as dependent variable, grain volume, FFD, width, perimeter and Hardness Index (HI) were recognized as the most important traits and explained more than 99.3% of total variation of TGW. The path analysis revealed that FFD has maximum direct effect on TGW followed by volume, whereas perimeter and width had relatively less direct effect on TGW. According to cluster analysis, landraces separated into 5 clusters, and cluster III and IV had the maximum and minimum average for the most traits, respectively. Our study provides new knowledge on the relations between TGW, grain morphology and grain quality in bread wheat, which may aid the improvement of wheat grain weight trait in further research.

Fine mapping of qKW7, a major QTL for kernel weight and kernel width in maize, confirmed by the combined analytic approaches of linkage and association analysis

Kernel weight (KWEI), a complex quantitative trait that is largely determined by kernel size, is a key component of grain yield in maize. In our previous studies, qKW7, a putative pleiotropic QTL associated with both KWEI and kernel width (KWID), was detected within the 7.02 bin region on chromosome 7 by both F2:3 population and recombinant inbred line (RIL) population from a Ye478 and Huangzaosi cross. Therefore, a series of backcross populations from the same cross have been developed for fine mapping qKW7. By using a large BC3F4 segregation population, the qKW7 QTL was mapped to a physical interval of 647 Kb with several genes. An association panel with 627 diverse inbred lines was used to process the association analysis, and the results indicated that three KWEI- and KWID-related quantitative trait nucleotides (QTNs) were tightly linked to qKW7. Sequence analysis revealed that all three detected QTNs were located within the gene region of GRMZM2G114706, which encodes an ankyrin protein kinase that regulates endosperm development. Finally, the putative genes responsible for qKW7 are discussed.

The Genetic Basis of Natural Variation in Kernel Size and Related Traits Using a Four-Way Cross Population in Maize.

Kernel size is an important component of grain yield in maize breeding programs. To extend the understanding on the genetic basis of kernel size traits (i.e., kernel length, kernel width and kernel thickness), we developed a set of four-way cross mapping population derived from four maize inbred lines with varied kernel sizes. In the present study, we investigated the genetic basis of natural variation in seed size and other components of maize yield (e.g., hundred kernel weight, number of rows per ear, number of kernels per row). In total, ten QTL affecting kernel size were identified, three of which (two for kernel length and one for kernel width) had stable expression in other components of maize yield. The possible genetic mechanism behind the trade-off of kernel size and yield components was discussed.

Fine-mapping of qGW4.05, a major QTL for kernel weight and size in maize.

BackgroundKernel weight and size are important components of grain yield in cereals. Although some information is available concerning the map positions of quantitative trait loci (QTL) for kernel weight and size in maize, little is known about the molecular mechanisms of these QTLs. qGW4.05 is a major QTL that is associated with kernel weight and size in maize. We combined linkage analysis and association mapping to fine-map and identify candidate gene(s) at qGW4.05.ResultsQTL qGW4.05 was fine-mapped to a 279.6-kb interval in a segregating population derived from a cross of Huangzaosi with LV28. By combining the results of regional association mapping and linkage analysis, we identified GRMZM2G039934 as a candidate gene responsible for qGW4.05. Candidate gene-based association mapping was conducted using a panel of 184 inbred lines with variable kernel weights and kernel sizes. Six polymorphic sites in the gene GRMZM2G039934 were significantly associated with kernel weight and kernel size.ConclusionThe results of linkage analysis and association mapping revealed that GRMZM2G039934 is the most likely candidate gene for qGW4.05. These results will improve our understanding of the genetic architecture and molecular mechanisms underlying kernel development in maize.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0768-6) contains supplementary material, which is available to authorized users.

Single nucleotide polymorphism tightly linked to a major QTL on chromosome 7A for both kernel length and kernel weight in wheat

Thousand-kernel weight (TKW) is one of the major components of grain yield in wheat (Triticum aestivum). Identifying major quantitative trait loci (QTLs) for TKW and developing effective markers are prerequisite for success in marker-assisted selection (MAS) to improve wheat yield through breeding. This study mapped a major QTL, designated as TaTKW-7AL, for increasing TKW on the long arm of chromosome 7A of ‘Clark’ to a 1.3-cM interval between single nucleotide polymorphism (SNP) markers IWB13913 and IWA5913. This QTL explained 19.7 % of the phenotypic variation for TKW. A QTL for increasing kernel length (KL), one of the major components of TKW, was mapped in the same interval as TaTKW-7AL, suggesting that increased TKW by the QTL in ‘Clark’ is most likely due to the increased KL. Association analysis on a diversity panel of 200 US winter wheat accessions also identified a haplotype of three SNP markers (IWB13913, IWB6693 and IWA5913) that were tightly associated with the both KL and TKW. The analysis of allele frequencies of the haplotype in the diversity panel suggested that the favorable allele of TaTKW-7AL has not been strongly selected for in practice and has potential to be used to improve grain yield in US hard winter wheat breeding. Two user-friendly flanking KASPar markers, IWB13913 and IWA5913, were developed for MAS of TaTKW-7AL.

Evidence for maternal control of seed size in maize from phenotypic and transcriptional analysis.

Seed size is an important component of grain yield and a key determinant trait for crop domestication. The Krug Yellow Dent long-term selection experiment for large and small seed provides a valuable resource to dissect genetic and phenotypic changes affecting seed size within a common genetic background. In this study, inbred lines derived from Krug Large Seed (KLS) and Krug Small Seed (KSS) populations and reciprocal F1 crosses were used to investigate developmental and molecular mechanisms governing seed size. Seed morphological characteristics showed striking differences between KLS and KSS inbred lines, and the reciprocal cross experiment revealed a strong maternal influence on both seed weight and seed size. Quantification of endosperm area, starchy endosperm cell size, and kernel dry mass accumulation indicated a positive correlation between seed size, endosperm cell number, and grain filling rate, and patterns of grain filling in reciprocal crosses mirrored that of the maternal parent. Consistent with the maternal contribution to seed weight, transcriptome profiling of reciprocal F1 hybrids showed substantial similarities to the maternal parent. A set of differentially expressed genes between KLS and KSS inbreds were found, which fell into a broad number of functional categories including DNA methylation, nucleosome assembly, and heat stress response. In addition, gene co-expression network analysis of parental inbreds and reciprocal F1 hybrids identified co-expression modules enriched in ovule development and DNA methylation, implicating these two processes in seed size determination. These results expand our understanding of seed size regulation and help to uncover the developmental and molecular basis underlying maternal control of seed size in maize.

Identification of QTLs for grain size and characterization of the beneficial alleles of grain size genes in large grain rice variety BL129

Grain size is one of the most important agronomic components of grain yield. Grain length, width and thickness are controlled by multiple quantitative trait loci (QTLs). To understand genetic basis of large grain shape and explore the beneficial alleles for grain size improvement, we perform QTL analysis using an F2 population derived from a cross between the japonica variety Beilu 129 (BL129, wide and thick grain) and the elite indica variety Huazhan (HZ, narrow and long grain). A total number of eight major QTLs are detected on three different chromosomes. QTLs for grain width (qGW), grain thickness (qGT), brown grain width (qBGW), and brown grain thickness (qBGT) explained 77.67, 36.24, 89.63, and 39.41% of total phenotypic variation, respectively. The large grain rice variety BL129 possesses the beneficial alleles of GW2 and qSW5/GW5, which have been known to control grain width and weight, indicating that the accumulation of the beneficial alleles causes large grain shape in BL129. Further results reveal that the rare gw2 allele from BL129 increases grain width, thickness and weight of the elite indica variety Huazhan, which is used as a parental line in hybrid rice breeding. Thus, our findings will help breeders to carry out molecular design breeding on rice grain size and shape.

Regulation of OsGRF4 by OsmiR396 controls grain size and yield in rice.

An increase in grain yield is crucial for modern agriculture(1). Grain size is one of the key components of grain yield in rice and is regulated by quantitative trait loci (QTLs)(2,3). Exploring new QTLs for grain size will help breeders develop elite rice varieties with higher yields(3,4). Here, we report a new semi-dominant QTL for grain size and weight (GS2) in rice, which encodes the transcription factor OsGRF4 (GROWTH-REGULATING FACTOR 4) and is regulated by OsmiR396. We demonstrate that a 2 bp substitution mutation in GS2 perturbs OsmiR396-directed regulation of GS2, resulting in large and heavy grains and increased grain yield. Further results reveal that GS2 interacts with the transcription coactivitors OsGIF1/2/3, and overexpression of OsGIF1 increases grain size and weight. Thus, our findings define the regulatory mechanism of GS2, OsGIFs and OsmiR396 in grain size and weight control, suggesting this pathway could be used to increase yields in crops.