QTLs for quantitative traits are influenced by genetic background (GB) and environment. Identification of QTL with GB independency and environmental stability is prerequisite for effective marker-assisted selection (MAS). In this study, QTLs and QTL × environment interactions affecting grain yield per plant (GY) and its component traits, filled grain number per panicle (FGN), panicle number per plant (PN) and 1000-grain weight (TGW) across six environments were dissected using two sets of reciprocal introgression lines (ILs) derived from the cross Lemont × Teqing and SNP genotypic data. ANOVA indicated that the differences among genotypes and environments within each set of ILs were highly significant for all traits. A total of 72 distinct QTLs for GY and its component traits including 15 for GY, 25 for FGN, 18 for PN, and 29 for TGW were detected over the six environments. Most QTLs (87.4%) showed significant QTL × environment interactions (QEIs) and appeared to be more or less environment-specific. Among 72 QTLs, 15 (20.8%) QTLs and 12 (16.7%) QEIs were commonly identified in both backgrounds, indicating QTL especially QEI for yield and its component traits had strong GB effects. Four QTL regions affecting GY and its component traits, including S1269707-S4288071, S16661497-S17511092, and S35861863-S36341768 on chromosome 3, and S4134205-S7643153 on chromosome 5, were detected in both backgrounds and coincided with cloned genes for yield-related traits. These regions can be the targeted in rice breeding for high yield potential through MAS. Application of QTL main effects and their environmental interaction effects in MAS was discussed in detail.
Salt is an abiotic stress factor that strongly affects soybean growth and production. A single dominant gene has been shown to confer salt tolerance in the soybean cultivar Tiefeng 8. The objective of the present study was to genetically map the salt-tolerance gene in an F2:3 population and a recombinant inbred line (RIL) population derived from a cross between two cultivated soybeans, Tiefeng 8 (tolerant) and 85-140 (sensitive). The F2:3 families and RILs were treated with 200 mmol L− 1 NaCl to evaluate salt tolerance. The F2:3 population showed 1 (42 tolerant): 2 (132 segregating): 1 (65 sensitive) segregation, indicating a single dominant gene for salt tolerance in Tiefeng 8. A sequence-characterized amplified region (SCAR) marker from a previously identified random amplified polymorphic DNA (RAPD) marker and four insertion/deletion polymorphism (InDel) markers were developed within the mapping region. Using these markers along with SSR markers, the salt-tolerance gene was mapped within 209 kb flanked by SCAR marker QS08064 and SSR marker Barcsoyssr_3_1301 on chromosome 3. Three markers that cosegregated with the salt tolerance gene and SCAR marker QS08064 were used to genotype 35 tolerant and 23 sensitive soybean accessions. These markers showed selection efficiencies of 76.2% to 94.2%. The results indicate that these markers will be useful for marker-assisted breeding and facilitating map-based cloning of the salt tolerance gene in soybean.
Soybean genotypes show diverse physiological responses to drought, but specific physiological traits that can be used to evaluate drought tolerance have not been identified. In the present study we investigated physiological traits of soybean genotypes under progressive soil drying and rewetting, using a treatment mimicking field conditions. After a preliminary study with eight soybean genotypes, two drought-tolerant genotypes and one susceptible genotype were grown in the greenhouse and subjected to water restriction. Leaf expansion rate, gas exchange, water relation parameters, total chlorophyll (Chl), proline contents of leaves, and root xylem pH were monitored in a time course, and plant growth and root traits were measured at the end of the stress cycle. Drought-tolerant genotypes maintained higher leaf expansion rate, net photosynthetic rate (Pn), Chl content, instantaneous water use efficiency (WUEi), % relative water content (RWC), water potential (ψw), and turgor potential (ψp) during progressive soil drying and subsequent rewetting than the susceptible genotypes. By contrast, stomatal conductance (gs) and transpiration rate (Tr) of tolerant genotypes declined faster owing to dehydration and recovered more sharply after rehydration than the same parameters in susceptible ones. Water stress caused a significant increase in leaf proline level and root xylem sap pH of both genotypes but tolerant genotypes recovered to pre-stress levels more quickly after rehydration. Tolerant genotypes also produced longer roots with higher dry mass than susceptible genotypes. We conclude that rapid perception and adjustment in response to soil drying and rewetting as well as the maintenance of relatively high Pn, %RWC, and root growth constitute the mechanisms by which drought-tolerant soybean genotypes cope with water stress.
Miniature inverted-repeat transposable elements (MITEs) are a type of DNA transposon frequently inserted into promoters, untranslated regions (UTR), introns, or coding sequences of genes. We found a 276-bp tourist-like MITE insertion in the 3′-UTR of a 16.9 kDa small heat shock protein gene (TaHSP16.9-3A) on chromosome 3A of common wheat. Haplotype analysis revealed two haplotypes, sHSP-W (wild type without MITE insertion) and sHSP-M (mutant with MITE insertion), present in wheat germplasm. Both semiquantitative PCR and quantitative real-time PCR analyses showed increased transcription levels of TaHSP16.9-3A in sHSP-M compared with those of sHSP-W after heat treatment at 42 °C. It appeared that the MITE insertion into the 3′-UTR enhances the transcription of TaHSP16.9-3A.
A field experiment was conducted to study the impact of the exclusion of the solar UV components on growth, photosynthesis and nitrogen metabolism in soybean (Glycine max) varieties PK-472, Pusa-24, JS 71-05, JS-335, NRC-7 and Kalitur. The plants were grown in specially designed UV exclusion chambers wrapped with filters to exclude UV-B or UV-A/B and transmitted all UV. Exclusion of UV significantly enhanced the growth of the aerial parts as well as the growth of the below ground parts in all of the six soybean varieties. Nitrate reductase activity (NRA) was significantly reduced, whereas leghemoglobin (Lb) content, total soluble protein, net photosynthesis (Pn) and α-tocopherol content were enhanced after UV exclusion. The exclusion of solar UV-A/B enhanced all parameters to a larger extent than the exclusion of solar UV-B in four of the six varieties of soybean except for NRC-7 and Kalitur. These two varieties responded more to UV-B exclusion compared to UV-A/B exclusion. A significant inverse correlation between the NRA and the number of nodules per plant was observed. The extent of response in all parameters was greater in PK-472 and JS71-05 than that in Kalitur and JS-335 after UV exclusion. The exclusion of UV augmented the growth of nodules, Lb content and α-tocopherol levels and conferred higher rates of Pn to support better growth of nodules. Control plants (+ UV-A/B) seemed to fulfill their N demand through the assimilation of NO3− resulting in lower symbiotic nitrogen fixation and higher NR activity.
The polymerase chain reaction (PCR) is particularly useful for plant pathogen detection. In the present study, multiplex PCR and SYBR Green real-time PCR were developed to facilitate the simultaneous detection of three important rice pathogens, Xanthomonas oryzae pv. oryzae, X. oryzae pv. oryzicola, and Burkholderia glumae. The unique PCR primer sets were designed from portions of a putative glycosyltransferase gene of X. oryzae pv. oryzae, an AvrRxo gene of X. oryzae pv. oryzicola, and an internal transcribed spacer (ITS) sequence of B. glumae. Using a multiplex PCR assay, X. oryzae pv. oryzae, X. oryzae pv. oryzicola, and B. glumae were detected in one PCR reaction that contained the newly developed primer set mix. Using SYBR Green real-time PCR assays, X. oryzae pv. oryzae, X. oryzae pv. oryzicola, and B. glumae were detected at 1, 1, and 10 fg μL− 1, respectively. These newly designed molecular assays are sensitive and could be reliable tools for pathogen detection and disease forecasting.
Breeding of forage maize should combine improvement achieved for grain with the specific needs of forage hybrids. Production stability is important when maize is used for silage if the planting area is not in the ideal agronomic environment. The objectives of the present research were: (i) to quantify environmental and genetic and their interaction effects on maize silage traits; (ii) to identify possible heterotic groups for forage aptitude and suggest the formation of potential heterotic patterns, and (iii) to identify suitable inbred line combinations for producing hybrids with forage aptitude. Forty-five hybrids derived from diallelic crosses (without reciprocals) among ten inbred lines of maize were evaluated in this study. Combined ANOVA over environments showed differences between genotypes (G), environments (E), and their interactions (GEI). Heritability (H2), and genotypic and phenotypic correlations were estimated to evaluate the variation in and relationships between forage traits. Postdictive and predictive AMMI models were fitted to determine the importance of each source of variation, G, E, and GEI, and to select genotypes simultaneously on yield, quality and stability. A predominance of additive effects was found in the evaluated traits. The heterotic pattern Reid-BSSS × Argentine flint was confirmed for ear yield (EY) and harvest index (HI). High and broad genetic variation was found for stover and whole plant traits. Some inbred lines had genes with differential breeding aptitude for ear and stover. Stover and ear yield should be the main breeding objectives in maize forage breeding.
High-density genetic markers are required for genotyping and linkage mapping in identifying genes from crops with complex genomes, such as barley. As the most common variation, single nucleotide polymorphisms (SNPs) are suitable for accurate genotyping by using the next-generation sequencing (NGS) technology. Reduced representation libraries (RRLs) of five barley accessions and one mutant were sequenced using NGS technology for SNP discovery. Twenty million short reads were generated and the proportion of repetitive sequences was reduced by more than 56%. A total of 6061 SNPs were identified, and 451 were mapped to the draft sequence of the barley genome with pairing reads. Eleven SNPs were validated using length polymorphic allele-specific PCR markers.
