Allelic diversity in the wild grass Aegilops tauschii is vastly greater than that in the D genome of common wheat (Triticum aestivum), of which Ae. tauschii is the source. Since the 1980s, there have been numerous efforts to harness a much larger share of Ae. tauschii's extensive and highly variable gene pool for wheat improvement. Those efforts have followed two distinct approaches: production of amphiploids, known as “synthetic hexaploids,” between T. turgidum and Ae. tauschii, and direct hybridization between T. aestivum and Ae. tauschii; both approaches then involve backcrossing to T. aestivum. Both synthetic hexaploid production and direct hybridization have led to the transfer of numerous new genes into common wheat that confer improvements in many traits. This work has led to release of improved cultivars in China, the United States, and many other countries. Each approach to D-genome improvement has advantages and disadvantages. For example, production of synthetic hexaploids can incorporate useful germplasm from both T. turgidum and Ae. tauschii, thereby enhancing the A, B, and D genomes; on the other hand, direct hybridization rapidly restores the recurrent parent's A and B genomes and avoids incorporation of genes with adverse effects on threshability, hybrid necrosis, vernalization response, milling and baking quality, and other traits, which are often transferred when T. turgidum is used as a parent. Choice of method will depend in part on the type of wheat being developed and the target environment. However, more extensive use of the so-far underexploited direct hybridization approach is especially warranted.
Cowpea (Vigna unguiculata) is an important legume crop with diverse uses. The species is presently a minor crop, and evaluation of its genetic diversity has been very limited. In this study, a total of 200 genic and 100 genomic simple sequence repeat (SSR) markers were developed from cowpea unigene and genome sequences, respectively. Among them, 27 genic and 27 genomic SSR markers were polymorphic and were used for assessment of genetic diversity and population structure in 105 selected cowpea accessions. A total of 155 alleles and 2.9 alleles per marker were identified, and the average polymorphic information content (PIC) value was 0.3615. The average PIC of genomic SSRs (0.3996) was higher than that of genic SSRs (0.3235), and most of the polymorphic genomic SSRs were composed of di- and trinucleotide repeats (51.9% and 37.0% of all loci, respectively). The low level of detected genetic diversity may be attributed to a severe genetic bottleneck that occurred during the cowpea domestication process. The accessions were classified by structure and cluster analysis into four subgroups that correlated well with their geographic origins or collection sites. The classification results were also consistent with the results from principal coordinate analysis and can be used as a guide during future germplasm collection and selection of accessions as breeding materials for cultivar improvement. The newly developed genic and genomic SSR markers described in this study will be valuable genomic resources for the assessment of genetic diversity, population structure, evaluation of germplasm accessions, construction of genetic maps, identification of genes of interest, and application of marker-assisted selection in cowpea breeding programs.
General and specific environmental adaptation of genotypes is the main goal of breeders. However, genotype-by-environment (G × E) interaction complicates the identification of genotypes for release. This study aimed at analyzing the effects of G × E interaction on the expression of important cassava traits using two multivariate analyses: additive main effects and multiplicative interaction (AMMI) and genotype stability index (GSI). Total carotene content (TCC), postharvest physiological deterioration (PPD), and reaction to viral diseases were significantly affected by G × E interaction effects. The low percent (%) variation due to genotype for cassava brown streak disease (CBSD) explained the influence of environment on CBSD expression. The % variation due to genotype for TCC was higher (96%) than variation due to environment (1.7%) and G × E interaction (2.4%) indicating a low interaction effect of environment on TCC accumulation. The % variation due to genotype was higher than % variation due to environment for all traits but CBSD root necrosis and CBSD on stems, indicating the influence of environment on the severity of the viral diseases. These findings indicate that screening for disease resistance requires multi-environment trials, whereas a single-environment trial suffices to screen for total carotene content.
Modern maize varieties have become more productive than ever, owing largely to increased tolerance of high plant density. However, the genetics of ear leaf traits under different densities remains poorly understood. In this study, Zhongdan 909 recombinant inbred lines (RILs) derived from a cross between Z58 and HD568 were genotyped for 3072 single-nucleotide polymorphisms (SNPs), and phenotyped for leaf length (LL), leaf width (LW), and leaf angle (LA) of the uppermost ear leaf under three planting densities (52,500, 67,500, and 82,500 plants ha− 1, respectively). A genetic map was then constructed using 1358 high-quality SNPs. The total length of the linkage map was 1985.2 cM and the average interval between adjacent markers 1.46 cM. With increasing density, LL and LW decreased from 63.68 to 63.02 cm and from 8.56 to 8.21 cm, respectively, while LA increased from 19.42° to 19.66°. All three traits had high heritabilities, of 0.75, 0.78, and 0.84, respectively. Using inclusive composite interval mapping, 23, 25, and 17 quantitative trait loci (QTL) were detected for LL, LW, and LA, respectively. Of these, 35 were simultaneously detected under two or three plant densities, while 30 were detected under only one. Sixty-five individual QTL explained 2.41% to 16.53% of phenotypic variation, while eight accounted for > 10%. These findings will help us understand the genetic basis of leaf traits in maize as well as the response of maize to increased plant density.
Stress induced by low temperature, which represents a widespread environmental factor, strongly affects maize growth and yield. However, the physiological characteristics and molecular regulatory mechanisms of maize seedlings in response to cold remain poorly understood. In this study, using RNA-seq, we investigated the transcriptome profiles of two sweet corn inbred lines, “Richao” (RC) and C5, under cold stress. A total of 357 and 455 differentially expressed genes (DEGs) were identified in the RC and C5 lines, respectively, 94 DEGs were detected as common DEGs related to cold response in both genotypes, and a total of 589 DEGs were detected as cold tolerance-associated genes. By combining protein function clustering analysis and significantly enriched Gene Ontology (GO) terms analysis, we suggest that transcription factors may play a dominating role in the cold stress response and tolerance of sweet corn. Furthermore, 74 differentially expressed transcription factors were identified, of those many genes involved in the metabolism and regulation of hormones. These results expand our understanding of the complex mechanisms involved in chilling tolerance in maize, and provide a set of candidate genes for further genetic analyses.
Thymus daenensis, a perennial herb, is often grown in areas that experience drought conditions during its growing period. Application of chitosan may compensate for the negative impact of drought stress on the yield of oil and secondary metabolites in Thymus. The interactive effects of foliar application of chitosan and drought stress on dry matter, essential oil yield, and selected physiological characteristics including photosynthetic pigments, osmotic adjustment, and lipid peroxidation of Thymus were investigated in a two-year study from 2014 to 2015. Treatments consisted of 0, 200, and 400 μL L− 1 chitosan applied to plants grown under field capacity, mild drought stress (50% field capacity), and severe drought stress (25% field capacity). Dry matter yield decreased substantially as drought stress intensified. However, essential oil content increased under stress conditions, with the highest essential oil yield obtained from plants under mild drought stress. Foliar application of chitosan compensated to some extent for dry matter and oil yield reduction of plants grown under drought stress. The highest essential oil yield (1.52 g plant− 1) was obtained by application of 400 μL L− 1chitosan under the mild stress condition in 2015 when plants were mature. The compensatory effect of chitosan in reducing the negative impact of stress conditions on dry matter and oil yield was due mainly to stimulation of osmotic adjustment through proline accumulation and reduction of lipid peroxidase level, which increased the integrity of cell membranes of thyme leaves.
Corchorus capsularis (white jute) and C. olitorius (dark jute) are the two principal cultivated species of jute that produce natural bast fiber of commercial importance. We have identified 4509 simple sequence repeat (SSR) loci from 34,163 unigene sequences of C. capsularis to develop a non-redundant set of 2079 flanking primer pairs. Among the SSRs, trinucleotide repeats were most frequent (60%) followed by dinucleotide repeats (37.6%). Annotation of the SSR-containing unigenes revealed their putative functions in various biological and molecular processes, including responses to biotic and abiotic signals. Eighteen expressed gene-derived SSR (eSSR) markers were successfully mapped to the existing single-nucleotide polymorphism (SNP) linkage map of jute, providing additional anchor points. Amplification of 72% of the 74 randomly selected primer pairs was successful in a panel of 24 jute accessions, comprising five and twelve accessions of C. capsularis and C. olitorius, respectively, and seven wild jute species. Forty-three primer pairs produced an average of 2.7 alleles and 58.1% polymorphism in a panel of 24 jute accessions. The mean PIC value was 0.34 but some markers showed PIC values higher than 0.5, suggesting that these markers can efficiently measure genetic diversity and serve for mapping of quantitative trait loci (QTLs) in jute. A primer polymorphism survey with parents of a wide-hybridized population between a cultivated jute and its wild relative revealed their efficacy for interspecific hybrid identification. For ready accessibility of jute eSSR primers, we compiled all information in a user-friendly web database, JuteMarkerdb (
In order to widen gene germplasm for kernel hardness in triticale, 60 synthetic hexaploid triticales were tested by the single kernel characterization system (SKCS) and secaloindoline alleles were identified by sequencing. Phenotyping showed that frequencies of soft, mixed and hard genotypes were 43.3%, 48.3%, and 8.4%, respectively. Genotyping identified three known secaloindoline-a alleles and four known secaloindoline-b alleles. Three new Sina-R1 alleles were designated Sina-R1d, Sina-R1e and Sina-R1f. Compared to Sina-D1c, Sina-R1d showed four point mutations causing changes in four amino acids, Sina-R1e had one point mutation causing an alanine to glycine substitution, and Sina-R1f possessed five point mutations but produced the same amino acid sequence as Sina-R1d. Two new Sinb-R1 alleles were discovered and designated Sinb-R1e and Sinb-R1f. Compared to Sinb-R1a, Sinb-R1e possessed a triplet-code insertion and four point mutations causing a cysteine insertion and two amino acid substitutions, and Sinb-R1f possessed three point mutations causing a cysteine insertion and a change of arginine to glycine. Association of hardness index with secaloindoline alleles indicated that SKCS of the Sina-R1d genotype was significantly lower than that of Sina-R1e, and Sinb-R1e was significantly lower than that of the Sinb-R1d genotype. A total of eight allelic combinations of secaloindoline genes were identified; Sina-R1d/Sinb-R1e and Sina-R1e/Sinb-R1d were relatively prevalent in the triticales surveyed. The results provide valuable information for further use of these germplasms in triticale breeding program due to the diverse polymorphism in secaloindoline genes.
Regulation of flowering is one of the key issues in crop yield. The Flowering Locus T (FT) gene is a well-known florigen, which integrates various signals from multiple flowering-regulation pathways to initiate flowering. We previously reported that there are at least six FT genes (GmFTL1-6) in soybean displaying flowering activity. However, the individual functions of genes GmFTL1-6 remain to be identified. In this study, we cloned the GmFTL2 promoter (GmFTLpro) from soybean (Glycine max) cultivar Tianlong 1 and analyzed its motifs bioinformatically and its expression patterns using both a transgenic approach and quantitative RT-PCR (qRT-PCR). In GmFTLpro::GUS transgenic lines, GUS signals were enriched in cotyledons, hypocotyledons, pollen, embryos, and root tips in a photoperiod-independent manner. qRT-PCR confirmed the GUS reporter results. Our results suggest that GmFTL2 expression is regulated by developmental and tissue-specific clues and plays roles in seedling establishment and the development of microgametophytes, embryos, and roots.
