Kernel Morphology Research Articles

Mapping QTLs controlling kernel dimensions in a wheat inter-varietal RIL mapping population.

Seven kernel dimension QTLs were identified in wheat, and kernel thickness was found to be the most important dimension for grain weight improvement. Kernel morphology and weight of wheat (Triticum aestivum L.) affect both yield and quality; however, the genetic basis of these traits and their interactions has not been fully understood. In this study, to investigate the genetic factors affecting kernel morphology and the association of kernel morphology traits with kernel weight, kernel length (KL), width (KW) and thickness (KT) were evaluated, together with hundred-grain weight (HGW), in a recombinant inbred line population derived from Nanda2419 × Wangshuibai, with data from five trials (two different locations over 3years). The results showed that HGW was more closely correlated with KT and KW than with KL. A whole genome scan revealed four QTLs for KL, one for KW and two for KT, distributed on five different chromosomes. Of them, QKl.nau-2D for KL, and QKt.nau-4B and QKt.nau-5A for KT were newly identified major QTLs for the respective traits, explaining up to 32.6 and 41.5% of the phenotypic variations, respectively. Increase of KW and KT and reduction of KL/KT and KW/KT ratios always resulted in significant higher grain weight. Lines combining the Nanda 2419 alleles of the 4B and 5A intervals had wider, thicker, rounder kernels and a 14% higher grain weight in the genotype-based analysis. A strong, negative linear relationship of the KW/KT ratio with grain weight was observed. It thus appears that kernel thickness is the most important kernel dimension factor in wheat improvement for higher yield. Mapping and marker identification of the kernel dimension-related QTLs definitely help realize the breeding goals.

Changes in kernel morphology and starch properties of high-amylose brown rice during the cooking process

Rice is principally consumed as cooked kernels. A high-amylose rice line, TRS, has a potential to positively impact human health. Though the properties of starch isolated from TRS kernels have been studied, the properties of cooked kernel remain to be resolved. In this study, the changes in kernel morphology and starch properties of brown TRS were investigated during cooking in boiling water. TRS kernel, which had polygonal, aggregate, elongated, and interior hollow starches from the inner to the outer of endosperm, showed different gelatinization properties during cooking. The polygonal starch was gelatinized most completely and fastest, the aggregate starch was partly gelatinized, and the elongated and interior hollow starches kept almost their intact status. The molecular weight distribution of starch in kernel did not show significant change, but starch crystalline structure was not wholly disrupted during the cooking process. The starch in cooked kernel had a very high resistance to digestion.

Dissection of Genetic Factors underlying Wheat Kernel Shape and Size in an Elite × Nonadapted Cross using a High Density SNP Linkage Map.

Wheat kernel shape and size has been under selection since early domestication. Kernel morphology is a major consideration in wheat breeding, as it impacts grain yield and quality. A population of 160 recombinant inbred lines (RIL), developed using an elite (ND 705) and a nonadapted genotype (PI 414566), was extensively phenotyped in replicated field trials and genotyped using Infinium iSelect 90K assay to gain insight into the genetic architecture of kernel shape and size. A high density genetic map consisting of 10,172 single nucleotide polymorphism (SNP) markers, with an average marker density of 0.39 cM/marker, identified a total of 29 genomic regions associated with six grain shape and size traits; ∼80% of these regions were associated with multiple traits. The analyses showed that kernel length (KL) and width (KW) are genetically independent, while a large number (∼59%) of the quantitative trait loci (QTL) for kernel shape traits were in common with genomic regions associated with kernel size traits. The most significant QTL was identified on chromosome 4B, and could be an ortholog of major rice grain size and shape gene or . Major and stable loci also were identified on the homeologous regions of Group 5 chromosomes, and in the regions of (6A) and (7A) genes. Both parental genotypes contributed equivalent positive QTL alleles, suggesting that the nonadapted germplasm has a great potential for enhancing the gene pool for grain shape and size. This study provides new knowledge on the genetic dissection of kernel morphology, with a much higher resolution, which may aid further improvement in wheat yield and quality using genomic tools.

A dense durum wheat × T. dicoccum linkage map based on SNP markers for the study of seed morphology

Durum wheat (Triticum turgidum L. var. durum) is a very important crop in the Mediterranean basin. Intense breeding activities are carried out to improve its productivity, quality, and resistance, and new genomic tools are essential to speed up the breeding progress. A segregating population of 136 recombinant inbred lines derived from a cross between the durum wheat cv. Simeto and the T. dicoccum accession Molise Colli was genotyped with the wheat 90k iSelect Infinium SNP assay. A linkage map was developed with 9,040 markers. Forty-five linkage groups were obtained, which covered all of the chromosomes. The map covered 2,879.3 cM, with a mean length of 205.6 cM per chromosome. The number of markers for each chromosome was from 418 (4B) to 978 (2B), with an average of 645.7. The parents of the genetic map differ according to several features, from traits linked to spike and kernel morphology to grain yield. Quantitative trait loci (QTL) analysis was performed for traits related to kernel morphology and thousand-kernel weight: six QTL were identified on chromosomes 1B, 2B, 3A, 3B, 4B and 7A, and 2 QTL on chromosomes 3B and 4B. Bioinformatic and synteny analyses with rice and Brachypodium genomes were performed based on the SNP sequences, with the identification of a candidate gene corresponding to a kinesin under the QTL located on chromosome 1B. The SNP-based Simeto × Molise Colli linkage map represents a useful tool to dissect out the genetic basis of traits of agronomic relevance for the genetic improvement of durum wheat.

Physical Features of Some Selected Nigerian Maize Cultivars

A morphological characteristic feature of one hundred Nigerian maize cultivars was established. This repository sought a baseline upon which Nigerian maize cultivars could be classified based on kernel morphology, germinating properties such as shoots length and percent of growth. Out of all the maize cultivars, forty eight were classified as Dent maize, five were found to be Pop maize, thirteen were Waxy maize and six were also classified as Sweet maize while fourteen were found to be Floury and Flint maize respectively. The information would serve as reference for the selection of appropriate Nigerian maize cultivars for specific use in food processing and allied industries.

Three‐Dimensional Seed Size and Shape QTL in Hexaploid Wheat (Triticum aestivum L.) Populations

ABSTRACTSeed size and shape are important traits that have been altered during domestication and are monitored in wheat (Triticum aestivum L.) breeding programs because they may impact yield and milling quality. Quantitative trait loci (QTL) for seed morphology were mapped in two doubled‐haploid (DH) wheat populations using three seed axes and elliptic Fourier descriptors of shape. In the Synthetic W7984 × Opata M85 (SynOpDH) population, 31 QTL were detected on all chromosomes except 3D, 4D, 5D, 6B, and 7B. Seed shape QTL in SynOpDH were independent of genes Q, Gpc‐B1, Ser5B, S1, S2, S3, and markers for rice (Oryza sativa L.) GW2 and GS3. Environmentally stable QTL on 1A and 2D, as well as a pleiotropic QTL on 5A were detected. QTL on chromosome 1A conditioned uniformly widened grains, 2D affected width, and 5A width and thickness. In the Cayuga × Caledonia DH population, 30 QTL affecting kernel morphology were detected on all chromosomes except 3A, 5D, 6A, 6B, 7A, and 7B. The most significant QTL in this population were on 3D affecting seed length and on 1D and 3B affecting uniform widening. Marker‐assisted selection of these QTL for complex dimensions of seed shape may assist in breeding cultivars with improved yield or quality.

Comparative analysis of autochthonous almond ( Prunus amigdalus Bastch) material and commercial varieties in the Castilla-La Mancha Region (Spain)

The Castilla-La Mancha Region is characterized by a large variety of microclimates, allowing the cultivation of species with different climate requirements. While the districts of “Sierra del Segura” and “Campos de Hellín” account for the largest almond growing area in the region. This comparative study is based on the existence of native almond material (local names De Santos and Daniel) which shows kernel morphology and nut quality quite similar to the two most well known commercial varieties of almonds: Marcona and Desmayo Largueta. The identification of this native almond material is of great importance due to its adaptation to local environmental conditions (low temperatures, drought, hot and dry summers) and its morphological similarities with these two almond commercial varieties. A set of 6 Prunus SSR markers were used to identify and differentiate a total of 27 almond samples taken in the “Sierra del Segura” district, including local plant material and material from commercial varieties as a reference. Ten different SSR profiles were discriminated. The number of alleles per locus ranged from seven to twelve with a total of 52 alleles for all loci and an average of 9 alleles per locus. The analysis showed that they share 58% of the studied alleles with one common allele size in both cases for all the SSRs studied. This is the first molecular characterization of native almond germplasm in the Castilla-La Mancha Region. The results provide useful information that could be included in the future almond germplasm bank.

Embryo and endosperm development in wheat (Triticum aestivum L.) kernels subjected to drought stress

The aim of the present work was to reveal the histological alterations triggered in developing wheat kernels by soil drought stress during early seed development resulting in yield losses at harvest. For this purpose, observations were made on the effect of drought stress, applied in a controlled environment from the 5th to the 9th day after pollination, on the kernel morphology, starch content and grain yield of the drought-sensitive Cappelle Desprez and drought-tolerant Plainsman V winter wheat (Triticum aestivum L.) varieties. As a consequence of water withdrawal, there was a decrease in the size of the embryos and the number of A-type starch granules deposited in the endosperm, while the development of aleurone cells and the degradation of the cell layers surrounding the ovule were significantly accelerated in both genotypes. In addition, the number of B-type starch granules per cell was significantly reduced. Drought stress affected the rate of grain filling shortened the grain-filling and ripening period and severely reduced the yield. With respect to the recovery of vegetative tissues, seed set and yield, the drought-tolerant Plainsman V responded significantly better to drought stress than Cappelle Desprez. The reduction in the size of the mature embryos was significantly greater in the sensitive genotype. Compared to Plainsman V, the endosperm cells of Cappelle Desprez accumulated significantly fewer B-type starch granules. In stressed kernels of the tolerant genotype, the accumulation of protein bodies occurred significantly earlier than in the sensitive variety.

Molecular mapping of quantitative trait loci for kernel morphology traits in a non-1BL.1RS×1BL.1RS wheat cross

The improvement of kernel morphology traits is an important goal in common wheat (Triticum aestivum L.) breeding programs because of their close relationship with grain yield and milling quality. The aim of this study was to map quantitative trait loci (QTL) for kernel morphology traits using 240 recombinant inbred lines derived from a cross between the non-1BL.1RS translocation cv. PH 82-2 and the 1BL.1RS translocation cv. Neixiang 188, grown in six environments in China. Inclusive composite interval mapping identified 71 main-effect QTL on 16 chromosomes for seven kernel morphology traits measured by digital imaging, viz. kernel length, width, perimeter, area, shape factor, factor form-density and width/length ratio. Each of these loci explained from 2.6 to 28.2% of the phenotypic variation. Eight QTL clusters conferring the largest effects on kernel weight and kernel morphology traits were detected on chromosomes 1BL.1RS (2), 2A, 4A, 4B, 6B, 6D and 7A. Fourteen epistatic QTL were identified for all kernel morphology traits except kernel width/length ratio, involving 24 main-effect QTL distributed on 13 chromosomes, and explaining 2.5–8.3% of the phenotypic variance. Five loci, viz. Sec-1 on 1BL.1RS, Glu-B1 on 1BL, Xcfe53 on 2A, Xwmc238 on 4B, and Xbarc174 on 7A, were detected consistently across environments, and their linked DNA markers may be used for marker-assisted selection in breeding for improved wheat kernel traits and grain yield.

Mutation of the maize sbe1a and ae genes alters morphology and physical behavior of wx-type endosperm starch granules

In maize, three isoforms of starch-branching enzyme, SBEI, SBEIIa, and SBEIIb, are encoded by the Sbe1a, Sbe2a, and Amylose extender ( Ae) genes, respectively. The objective of this research was to explore the effects of null mutations in the Sbe1a and Ae genes alone and in combination in wx background on kernel characteristics and on the morphology and physical behavior of endosperm starch granules. Differences in kernel morphology and weight, starch accumulation, starch granule size and size distribution, starch microstructure, and thermal properties were observed between the ae wx and sbe1a ae wx plants but not between the sbe1a wx mutants when compared to wx. Starch from sbe1a ae wx plants exhibited a larger granule size with a wider gelatinization temperature range and a lower endotherm enthalpy than ae wx. Microscopy shows weaker iodine staining in sbe1a ae wx starch granules. X-ray diffraction revealed A-type crystallinity in wx and sbe1a wx starches and B-type in sbe1a ae wx and ae wx. This study suggests that, while the SBEIIb isoform plays a dominant role in maize endosperm starch synthesis, SBEI also plays a role, which is only observable in the presence of the ae mutation.

Evaluation of the effect of moisture content on cereal grains by digital image analysis

Physical appearance and kernel morphology significantly affect the grade of a harvested crop in addition to other factors such as test weight, percentage of foreign matter and constituent components. Moisture content of grain can potentially affect the physical appearance and kernel morphology. The objective of this study was to evaluate the effect of moisture content on the classification capability of colour, morphology and textural features of imaged grains. Colour images of individual kernels and bulk samples of three grain types, namely Canada Western Amber Durum (CWAD) wheat, Canada Western Red Spring (CWRS) wheat and barley were acquired using a machine vision system. The grain kernels were conditioned to 12%, 14%, 16%, 18% and 20% moisture contents before imaging. Previously developed algorithms were used to extract 123 colour, 56 textural features from bulk sample images and 123 colour, 56 textural, 51 morphological features from individual kernel images. The extracted features were analysed for the effect of moisture content. Statistical classifiers and a back propagation neural network model were used for classifying the grain bulk at different moisture contents. The colour and textural features of bulk grain images were affected by the moisture content more than that of the single kernel images.

QTL analysis of kernel size and shape in two hexaploid wheat mapping populations

Kernel size and shape in wheat are important because of their relationship with yield and milling quality. This paper reports QTL analyses of kernel morphology in two hexaploid wheat mapping populations, grown in NY and CA. Kernel morphology was evaluated through a new and improved method, combining measurements from two orthogonal pictures. Single marker regression showed that several genomic positions, scattered through the genome, were related to kernel size and shape, in both populations. The direction of allele effects was consistent between environments, although the LOD scores varied considerably. Composite interval mapping revealed QTLs on all seven homoeologous groups, considering both populations. For the QTLs detected through this method, the signal and magnitude of additive effects were similar between environments, indicating small QTL × environment interaction. In the population W7984 × Opata 85, the strongest signal was detected on the chromosome 5B, for kernel length. In the population AC Reed × Grandin, the most important QTLs were detected on chromosome 2D, affecting the lateral dimensions of the kernel. This study agreed with previous reports that the genetic control of kernel length and width are largely independent. Additionally, it was shown that QTLs detected on different mapping populations, with identical evaluation methods, can be very distinct.

Association Mapping of Kernel Size and Milling Quality in Wheat (Triticum aestivum L.) Cultivars

Association mapping is a method for detection of gene effects based on linkage disequilibrium (LD) that complements QTL analysis in the development of tools for molecular plant breeding. In this study, association mapping was performed on a selected sample of 95 cultivars of soft winter wheat. Population structure was estimated on the basis of 36 unlinked simple-sequence repeat (SSR) markers. The extent of LD was estimated on chromosomes 2D and part of 5A, relative to the LD observed among unlinked markers. Consistent LD on chromosome 2D was <1 cM, whereas in the centromeric region of 5A, LD extended for approximately 5 cM. Association of 62 SSR loci on chromosomes 2D, 5A, and 5B with kernel morphology and milling quality was analyzed through a mixed-effects model, where subpopulation was considered as a random factor and the marker tested was considered as a fixed factor. Permutations were used to adjust the threshold of significance for multiple testing within chromosomes. In agreement with previous QTL analysis, significant markers for kernel size were detected on the three chromosomes tested, and alleles potentially useful for selection were identified. Our results demonstrated that association mapping could complement and enhance previous QTL information for marker-assisted selection.

Camera Attachment for Automatic Measurement of Single-Wheat Kernel Size on a Perten SKCS 4100

A simple camera was attached to a Perten Single-Kernel Characterization System (SKCS) 4100 to measure single kernel morphology as they are fed through the SKCS. The camera and lighting were positioned above the SKCS weigher bucket. Each image of a wheat kernel was captured and processed in 15 to 60 ms. Image measurements included kernel area, length, and width.

Genetic diversity among maize (Zea mays L.) landraces assessed by RAPD markers

The genetic relationships among 81 maize accessions consisting 79 landraces and two improved varieties, maintained by farmers in southern Brazil were investigated using Random Amplified Polymorphic DNA (RAPD). Thirty-two highly informative primers amplified 255 markers of which 184 (72.2%) were polymorphics. Based on the RAPD markers, a dendrogram was constructed using the UPGMA method. The range of genetic similarity was from 0.78 to 0.91. The molecular data grouped the accessions into two main clusters, which were correlated according to kernel colors. Small clusters were seen associated to characteristics, such as kernel morphology. The analysis of the molecular data revealed that maize management adopted by small-scale farmers has contributed to the maintenance of genetic variability and since field isolation is a regular practice, variety identities have been preserved. These results will be useful to establish and maintain a germplasm collection of landrace maize and may guide us in designing strategies that maximize the utility of maize genetic resources.

Molecular marker analysis of kernel size and shape in bread wheat

AbstractThe economic value of wheat grain is determined by the kernel morphology which is an important parameter for manufacturing different food products requiring specific grain characteristics. Although kernel size and shape have emerged as important breeding objectives, not much information is available about the number or location of associated gene(s)/quantitative trait loci. In the present study, a recombinant inbred line population of 106 plants (F7) was phenotyped for four traits, namely kernel length, width, weight and factor form density (FFD) and genotyped with different polymerase chain reaction‐based markers. Transgressive segregants were observed for all the traits and genetic correlation studies showed positive correlations between the majority of the traits. The number of markers associated with each trait ranged from two to nine and the phenotypic contribution by an individual marker ranged from 3.3 to 16.6%. Many of the markers showed linkage to more than one trait. Strategies for improving the wheat grain quality traits and the utility of such markers in marker‐assisted selection (MAS) efforts are discussed.

Analysis of factors influencing milling yield and their association to other traits by QTL analysis in two hexaploid oat populations

Milling yield, or the grain weight from which 100 kg of rolled groats is obtained upon milling, is an important quality characteristic of cultivated oat (Avena sativa L.). Kernel morphology and the groat (caryopsis) percentage of the whole kernel including hull are factors that influence milling yield. We mapped QTLs for kernel area, kernel length, kernel width, and groat percentage in two populations of 137 recombinant inbred lines by RFLP and AFLP analysis to evaluate the prospects of marker-assisted selection (MAS). Phenotypic correlations between kernel morphology traits and groat percentage were not significant. For kernel morphology traits and groat percentage, one to five QTLs were detected, explaining 7.0–60.7% of the total phenotypic variance depending on the trait. One QTL for kernel length in each population and one QTL for kernel width in one population were found at the same location as a QTL for groat percentage, indicating that a change in kernel size or shape could have an influence on groat percentage. The positions and effects of QTLs for kernel morphology and groat percentage were compared to QTLs detected previously for chemical grain composition (oil andβ-glucanconcentration) and agronomic traits to evaluate the selection response on these traits through MAS. Several regions of the oat genome were identified that contained clusters of QTLs influencing two or more traits. While the allele from one parent at a QTL could simultaneously improve two or more traits in one population, it could have opposite effects on the same traits at another QTL or in the other population. Associations among traits were complex and will require careful consideration when employing QTL-marker associations in MAS to avoid negative selection response. Future research to discover candidate genes for those QTL clusters could provide information about trait associations and help in designing selection programs.

Recurrent Selection for Kernel Weight in Spring Wheat

Increasing kernel weight has been proposed as a method to increase flour extraction in spring wheat (Triticum aestivum L.). Recurrent selection was initiated to increase kernel weight while maintaining genetic variation for the unselected traits. Our objectives were to determine (i) genetic gain for kernel weight after eight cycles of selection, (ii) the indirect effects of the selection for kernel weight on other agronomic traits, kernel morphology, milling fractions, and grain protein concentration, and (iii) the level of genetic variability among lines within selection cycles for kernel weight and unselected traits. Ten lines, selected for high kernel weight, were originally intermated to form the base population. About 20 F2 plants with the highest kernel weight were selected (∼2% of the population), and about three of their F3 progeny were intermated to form the next cycle. This procedure was repeated for eight cycles, with an average of 60 crosses per cycle. Forty random lines from each cycle were used to evaluate agronomic traits in three environments. Kernel weight increased linearly at about 4.5% cycle−1 Cycle means did not differ for plant height and grain yield, but tillers per square meter and kernels per spike decreased 2.4 and 1.6% per cycle, respectively. Spikelets per spike, kernels per spikelet, test weight, and days to heading decreased, whereas spike length increased in response to selection for kernel weight. The proportion of bran and shorts decreased, and flour extraction and grain protein concentration increased 0.58 and 0.16% cycle−1, respectively. No clear trend towards decreased genetic variance for kernel weight was observed since gain was linear over eight cycles. The observed gain from selection and heritability estimates point to kernel weight being controlled by several genes with small effects. Selection for increased kernel size in this population resulted in increased flour yield.

A segmental gene duplication generated differentially expressed myb-homologous genes in maize.

The myb-homologous p1 gene regulates the synthesis of flavonoid pigments in maize kernel pericarp and cob; these floral organs are greatly modified in size and shape compared with their counterparts in teosinte, the progenitor of maize. To elucidate the molecular evolution of the p1 gene in relation to its expression and possible functions in maize and teosinte, we have isolated a second maize gene (p2) that is highly homologous with the p1 gene, and a related gene (p2-t) from Zea mays subsp parviglumis. We present evidence that the maize p1 and p2 genes were generated by duplication of an ancestral p gene (p(pre)) and its downstream sequences; the duplicated 3' flanking sequences were inserted upstream of the p(pre) gene, thereby changing its transcription pattern. This model accounts for the structural organization and the observed differential expression of the p1 and p2 genes: p1 transcripts accumulate in kernel pericarp, cob, tassel glumes, and silk, whereas p2 transcripts are found in developing anther and silk. The duplication is estimated to have occurred 2.75 million years ago; subsequently, multiple retroelements have been inserted between the p1 and p2 genes. Our results demonstrate the evolution of a single gene into a compound locus containing two component genes with different tissue specificities. Expression of the p1 gene in the kernel pericarp may have provided a selective advantage during the evolution of maize kernel morphology.

KERNEL MORPHOLOGY VARIATION IN A POPULATION DERIVED FROM A SOFT BY HARD WHEAT CROSS AND ASSOCIATIONS WITH END-USE QUALITY TRAITS

Physical attributes, including kernel morphology, are used to grade wheat, and indicate wheat milling and baking quality (MBQ). Using a recombinant inbred population derived from a soft by hard wheat cross, this study quantified kernel traits' sources of variation, studied their heritability, and relationships between morphological and MBQ traits. Transgressive segregation occurred for all traits. Thousand-kernel weight (TKW) and kernel texture (NIR-T) were primarily influenced by genotype and test weight (TW) mainly by year. NIR-T had the highest heritability. Low genetic correlation (GCOR) between kernel length (LEN) and width (WID) suggest independent inheritance. NIR-T and LEN, or WID, showed low GCOR. Thus, it is genetically feasible to produce cultivars with any kernel texture and LEN, or WID, combination. No GCOR was found between TW and flour milling yield (FY), TKW, NIR-T or kernel morphology. GCOR showed that harder wheats had greater FY. Traits' low correlations call for studies clarifying the efficacy of using kernel traits in wheat classification or end-use quality prediction.