Major Gene Model Research Articles

Identification of Putative Quantitative Trait Loci for Improved Seed Oil Quality in Peanuts.

Improving seed oil quality in peanut (Arachis hypogaea) has long been an aim of breeding programs worldwide. The genetic resources to achieve this goal are limited. We used an advanced recombinant inbred line (RIL) population derived from JH5 × KX01-6 to explore quantitative trait loci (QTL) affecting peanut oil quality and their additive effects, epistatic effects, and QTL × environment interactions. Gas chromatography (GC) analysis suggested seven fatty acids components were obviously detected in both parents and analyzed in a follow-up QTL analysis. The major components, palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2), exhibited considerable phenotypic variation and fit the two major gene and minor gene mixed-inheritance model. Seventeen QTL explained 2.57-38.72% of the phenotypic variation in these major components, with LOD values of 4.12-37.56 in six environments, and thirty-five QTL explained 0.94-32.21% of the phenotypic variation, with LOD values of 5.99-150.38 in multiple environments. Sixteen of these QTL were detected in both individual and multiple environments. Among these, qFA_08_1 was a novel QTL with stable, valuable and major effect. Two other major-effect QTL, qFA_09_2 and qFA_19_3, share the same physical position as FAD2A and FAD2B, respectively. Eleven stable epistatic QTL involving nine loci explained 1.30-34.97% of the phenotypic variation, with epistatic effects ranging from 0.09 to 6.13. These QTL could be valuable for breeding varieties with improved oil quality.

Genetic analysis of stay green related traits in maize with major gene plus polygenes mixed model.

Maize is one of the main food crops in the world, and cultivating high-yield and high-quality maize varieties is of great significance in addressing food security issues. Leaves are crucial photosynthetic organs in maize, and leaf senescence can result in the degradation of chlorophyll. This, in turn, impacts photosynthetic activity and the accumulation of photosynthetic products. Delaying leaf senescence and increasing carbon assimilation can enhance grain yield and biomass production. The stay green of maize is an important trait closely related to yield, feed quality and resistance. Therefore, this study employed multi-generation joint analysis of major genes and a polygene model to investigate the genetic inheritance of stay green-related traits. Four populations (P1, P2, F1 and F2) were obtained by crossing T01 (stay green) × Xin3 (non-stay green) and T01 (stay green) × Mo17 (non-stay green) under two environments. Six stay green-related traits, including visual stay green (VSG), number of green leaves (GLNM), SPAD value of ear leaf at anthesis (SPADS), SPAD value of ear leaf at maturity (SPADM), absolute green leaf area (GLAD), grain yield per plant (GYP), displayed continuous variations with kurtosis and skewness values of absolute value less than 1 and distribution close to normal. They were characterized by typical inheritance of quantitative traits, with these traits demonstrating the transgressive segregation. The correlation analysis among the traits revealed that five stay green traits have a positive impact on yield. VSG, GLNM and SPADM in the two populations were regulated by the two major genes of additive effects plus additive-dominance polygene model with a major gene heritability varying from 89.03 to 95.95% in the F2 generation. GLAD in TMF2 was controlled by two major genes of equal-additive dominance effects with high heritability (93.47%). However, in TXF2, GLAD was regulated by two major genes of additive-dominance interaction effects plus additive-dominance polygene model. These results provide important genetic information for breeding, which could guide the improvement of stay green-related traits. They also lay a foundation for quantitative trait loci mapping of the stay stay-green traits in maize.

Heterosis and Mixed Genetic Analysis of Flowering Traits in Cross Breeding of Day-Neutral Chrysanthemum (Asteraceae)

Day-neutral multiflora chrysanthemums can flower throughout the year without being influenced by daylength and have great application value in gardens. Studying heterosis and the genetic basis of important traits in day-neutral chrysanthemums can accelerate the breeding of new cultivars. In this research, a genetic population was constructed by crossing 135 F1 hybrid progeny from the day-neutral chrysanthemum ‘82-81-19’ (female parent) and the late-flowering chrysanthemum ‘388Q-76’ (male parent). Six traits, including abnormal (crown) bud, plant height, plant crown width, budding date, full flowering date, and number of petal layers, were selected for inheritance and heterosis analyses, and a single-generation major gene plus polygene mixed inheritance model was used to perform mixed inheritance analysis on these traits. The results indicated that the six traits were widely segregated in the F1 population, with the coefficient of variation (CV) ranging from 30% to 84%. The phenomena of heterosis and extra-parent segregation existed generally in F1 progeny, and the ratio of heterosis value of mid-parents (RHm) for the six traits was 45.5%, 2%, 2%, 6%, 6%, and −0.3%, respectively. The mixed genetic analysis showed that the abnormal (crown) bud and budding date were fitted to the B-3 model and controlled by two pairs of additive major genes. The plant height and plant crown width were fitted to the A-0 model, and no major gene was detected. The full flowering date was fitted to the A-1 model and was controlled by one pair of major genes. The number of petal layers was fitted to the B-1 model and controlled by two pairs of additive–dominant major genes. The heritabilities of major genes for abnormal bud, budding date, full flowering date, and the number of petal layers were 1.0, 0.9871, 0.7240, and 0.5612, respectively, indicating that these traits were less affected by environmental factors. Using a percentile scoring method, eight day-neutral chrysanthemum genotypes were selected from the hybrid progeny.

Genetic analysis of mixed models of fruit sugar-acid fractions in a cross between jujube (Ziziphus jujuba Mill.) and wild jujube (Z. acido jujuba).

Chinese jujube (Ziziphus jujuba Mill.), an economically significant species in the Rhamnaceae family, is a popular fruit tree in Asia. The sugar and acid concentrations in jujube are considerably higher than those in other plants. Due to the low kernel rate, it is extremely difficult to establish hybrid populations. Little is known about jujube evolution and domestication, particularly with regard to the role of the sugar and acid components of jujube. Therefore, we used cover net control as a hybridization technique for the cross-breeding of Ziziphus jujuba Mill and 'JMS2' and (Z. acido jujuba) 'Xing16' to obtain an F1 population (179 hybrid progeny). The sugar and acid levels in the F1 and parent fruit were determined by HPLC. The coefficient of variation ranged from 28.4 to 93.9%. The sucrose and quinic acid levels in the progeny were higher than those in the parents. The population showed continuous distributions with transgressive segregation on both sides. Analysis by the mixed major gene and polygene inheritance model was performed. It was found that glucose is controlled by one additive-dominant major gene and polygenes, malic acid is controlled by two additive-dominant major genes and polygenes, and oxalic acid and quinic acid are controlled by two additive-dominant-epistatic major genes and polygenes. The results of this study provide insights into the genetic predisposition and molecular mechanisms underlying the role of sugar acids in jujube fruit.

Familial aggregation of esophageal cancer.

Familial aggregation of esophageal cancer.

Inheritance analysis of fruit-related traits in Chinese cherry [Cerasus pseudocerasus (Lindl.) G.Don] breeding progenies

• Heredity variation and inheritance tendency were analyzed for eighteen fruit-related traits of F 1 population derived from 'Hongfei' × 'Pujianghonghua' of Chinese cherry for two years. • Significant levels of transgressive heterosis were observed for total soluble solid, anthocyanin content and fruit stalk length, whereas negative heterosis detected in fruit weight and size. • The fruit-related traits were most likely controlled by two pairs of major genes, which exerted both additive effects and dominant effects. • The heritability of major gene controlling maturity date and fruit development period was high, while that of major genes controlling fruit quality traits was low. Chinese cherry [ Cerasus pseudocerasus (Lindl.) G.Don] is one of the important stone fruits in China. To explore the heredity variation of fruit-related traits, we investigated 18 fruit-related traits of the F 1 segregating population around 700 individuals derived from 'Hongfei' × 'Pujianghonghua' of Chinese cherry for two years. The mixed major gene and polygene inheritance model method was also evaluated for their fitness in relating to the traits. The results showed that the main fruit traits had different degrees of variation, with the coefficient of variation ranging from 4.76 to 26.71% (72.23% for anthocyanin content) in 2021, and from 4.71 to 21.57% in 2022. Significant levels of transgressive heterosis were observed for fruit stalk length, total soluble solid and anthocyanin content, whereas negative heterosis was detected in fruit weight and size. The most suitable genetic model for fruit maturity date and fruit development period was 2MG-ADI and 2MG-AD, respectively, and the heritability of major gene was greater than 90%. The optimal genetic model for ten fruit size and flavor related traits was 2MG-AD or 2MG-EA, which were controlled by two pairs of major genes with additive-dominant effect or equal-additive effect, with the major gene heritability being less than 45%. The additive effects of the fruit-related traits were mostly positive, while the dominant effects were mainly negative. These results provide a theoretical basis for quantitative trait locus (QTL) mapping and marker-assisted breeding of fruit-related traits in Chinese cherry.

Novel candidate loci for morpho-agronomic and seed quality traits detected by targeted genotyping-by-sequencing in common bean.

Phaseolus vulgaris L., known as common bean, is one of the most important grain legumes cultivated around the world for its immature pods and dry seeds, which are rich in protein and micronutrients. Common bean offers a cheap food and protein sources to ameliorate food shortage and malnutrition around the world. However, the genetic basis of most important traits in common bean remains unknown. This study aimed at identifying QTL and candidate gene models underlying twenty-six agronomically important traits in common bean. For this, we assembled and phenotyped a diversity panel of 200P. vulgaris genotypes in the greenhouse, comprising determinate bushy, determinate climbing and indeterminate climbing beans. The panel included dry beans and snap beans from different breeding programmes, elite lines and landraces from around the world with a major focus on accessions of African, European and South American origin. The panel was genotyped using a cost-conscious targeted genotyping-by-sequencing (GBS) platform to take advantage of highly polymorphic SNPs detected in previous studies and in diverse germplasm. The detected single nucleotide polymorphisms (SNPs) were applied in marker-trait analysis and revealed sixty-two quantitative trait loci (QTL) significantly associated with sixteen traits. Gene model identification via a similarity-based approach implicated major candidate gene models underlying the QTL associated with ten traits including, flowering, yield, seed quality, pod and seed characteristics. Our study revealed six QTL for pod shattering including three new QTL potentially useful for breeding. However, the panel was evaluated in a single greenhouse environment and the findings should be corroborated by evaluations across different field environments. Some of the detected QTL and a number of candidate gene models only elucidate the understanding of the genetic nature of these traits and provide the basis for further studies. Finally, the study showed the possibility of using a limited number of SNPs in performing marker-trait association in common bean by applying a highly scalable targeted GBS approach. This targeted GBS approach is a cost-efficient strategy for assessment of the genetic basis of complex traits and can enable geneticists and breeders to identify novel loci and targets for marker-assisted breeding more efficiently.

Resource Screening and Inheritance Analysis of Fusarium oxysporum sp. conglutinans Race 2 Resistance in Cabbage (Brassica oleracea var. capitata).

Cabbage (Brassica oleracea var. capitata) Fusarium wilt (CFW) is a disease that poses a critical threat to global cabbage production. Screening for resistant resources in order to support the breeding of resistant cultivars is the most reliable approach to control this disease. CFW is caused by Fusarium oxysporum f. sp. conglutinans (Foc), which consists of two physiological races (race 1 and 2). While many studies have focused on resistance screening, gene mining, and inheritance-based research associated with resistance to Foc race 1, there have been few studies specifically analyzing resistance to Foc race 2, which is a potential threat that can overcome type A resistance. Here, 166 cabbage resources collected from around the world were evaluated for the resistance to both Foc races, with 46.99% and 38.55% of these cabbage lines being resistant to Foc race 1 and race 2, respectively, whereas 33.74% and 48.80% were susceptible to these two respective races. Of these 166 analyzed cabbage lines, 114 (68.67%) were found to be more susceptible to race 2 than to race 1, and 28 of them were resistant to race 1 while susceptible to race 2, underscoring the highly aggressive nature of Foc race 2. To analyze the inheritance of Foc race 2 resistance, segregated populations derived from the resistant parental line ‘Badger Inbred 16’ and the susceptible one ‘01-20’ were analyzed with a major gene plus polygene mixed genetic model. The results of this analysis revealed Foc race 2-specific resistance to be under the control of two pairs of additive-dominant-epistatic major genes plus multiple additive-dominant-epistatic genes (model E). The heritability of these major genes in the BC1P1, BC1P2, and F2 generations were 32.14%, 72.80%, and 70.64%, respectively. In summary, these results may aid in future gene mining and breeding of novel CFW-resistant cabbage cultivars.

Genetic analysis of leaf trichome density using mixed major gene plus polygene inheritance model in Brassica rapa ssp. chinensis

ABSTRACT Leaf trichome is an important trait for stress-resistance breeding in Brassica crops, but its scientific evaluation and identification are rarely reported. To investigate the inheritance of leaf trichome in non-heading Chinese cabbage, two inbred lines, ‘14XS23W’ (glabrous) and ‘14XS23Y’ (hirsute), were used to generate F1 and F2 populations for joint analysis using a mixed major genes plus polygene inheritance model. The density of adaxial leaf trichomes was controlled by two pairs of additive-dominance-epistasis major genes plus additive-dominance polygenes. The broad-sense heritabilities of the major genes were 93.8% and 85.51%, respectively, for greenhouse and open-field conditions. However, the density of the abaxial leaf trichome was controlled by two pairs of additive-dominance-epistasis major genes plus additive dominance-epistasis polygenes. The broad-sense heritabilities of the major genes were 91.45% and 72.20%, while the polygenes were 0% and 14.5%, respectively, for greenhouse and open field environments. These results indicated that trichome density in non-heading Chinese cabbage was primarily controlled by two pairs of major genes with high heritability, implying that this trait is suitable for rapid selection in early generations.

Genetic Analysis and QTL Mapping of Parthenocarpy in <i>Cucumis sativus</i> L

Breeding of cucumber cultivars with high parthenocarpy rate are the prerequisite that ensuring yield and quality under undesirable environment. The mixed major gene plus polygene inheritance model was used to analyze cucumber parthenocarpy trait in the six generations, including P 1 , P 2 , F 1 , BC 1 , BC 2  and F 2 , derived from a cross between the highly parthenocarpic line DDX and low parthenocarpic line ZK. The major-effect quantitative trait locus (QTL) was identified by genome-wide comparison of single nucleotide polymorphisms (SNPs) between high- and low- parthenocarpy rate F 2  pools, and confirmed by traditional QTL mapping with genetic map. Genetic analysis showed that the genetic model E-2, mixed two additive-dominant-epistatic major genes and additive-dominant polygenes, is the best-fitting genetic model for cucumber parthenocarpy phenotype. A major-effect QTL, namely  par2.1 , were identified by the method of Δ(SNP_index).  par2.1  was confirmed by traditional markers based QTL mapping method with least likelihood (LOD) peak score of 12.6, genetic distance of 11.5cM and accounting for 26.6% of the total phenotypic variance.  par2.1  was narrowed down to a 765kb region through comparison of markers physical locations on chromosome 2. The major-effect QTL,  par2.1  on Chr2, for parthenocarpy identified by this study was not reported previously. Our findings shed light on the genetic architecture underlying cucumber parthenocarpy trait, and lay a solid basis for innovation of cucumber parthenocarpy germplasm and breed of new cucumber varieties with high parthenocarpy.

Variation and inheritance of the degree of style branching in hybrids of Iris dichotoma × I. domestica

The degree of style branching is an important characteristic for classification, reproduction and ecological function in the Iridaceae family. We established 6 generations derived from Iris dichotoma and I. domestica, and calculated the style branch ratio (the ratio of each style branch to the whole style in length) to express the branching degree of style. The variation of style branch ratio was analyzed and the genetic mechanism of style branch ratio was explored by using the major gene plus polygene mixed inheritance analysis model. The style branch ratios of the progeny were between their parents, in which the style branch ratios of F1 (I. dichotoma × I. domestica) were intermediate between P1 (I. dichotoma) and P2 (I. domestica); BC1Dic (F1 × P1) and BC1Dom (F1 × P2) were close to their recurrent parents, respectively. F2 displayed a wide and continuous variation in the degree of style branching. E-1 (MX2-ADI-AD) was the optimal genetic model for the style branch ratio, indicating that it was controlled by two major genes with additive, dominant, and epistatic effects plus polygene with additive and dominant effects. In major genes, the unbranched was dominant, but in polygene the branched was dominant. The additive effect of polygene was the largest in all effects. The major gene heritabilities in BC1Dic, BC1Dom, and F2 were 32.76%, 39.81%, and 37.63%, respectively. The polygene heritability in BC1Dic, BC1Dom and F2 were 0%, 36.05% and 46.40%, respectively. Therefore, we obtained a good material with continuous variation in the degree of style branching for further research on its reproductive and ecological functions; our findings lay the foundation for QTL mapping to further study the genetic mechanism of the degree of style branching.

Germplasm screening and inheritance analysis of resistance to cabbage black rot in a worldwide collection of cabbage (Brassica oleracea var. capitata) resources

Xanthomonas campestris pv. campestris (Xcc) is the causal agent of cabbage (Brassica oleracea var. capitata) black rot (BR) that leads to severe yield losses worldwide. Cultivation and application of resistant cultivars is the most desirable way to control BR. However, due to the lack of BR-resistant germplasm resources and an unclear understanding of the resistance inheritance as well as the controlling gene, the breeding process has been seriously hindered. To identify new BR resistance sources to Xcc race 1, 162 cabbage accessions collected worldwide were evaluated using the spray inoculation method. In total, 64.2% of them were susceptible, and only four germplasms were highly resistant, including two inbred lines (‘05-574-323’ and ‘MD219’) and two hybrids (‘Qinglian’ and ‘Dadilv 2’). Further, to define the genetic characteristics of resistance, a mixed major gene plus polygene inheritance model was used to analyze BR resistance in six populations (P1, P2, F1, B1, B2, and F2) derived from the resistant parent ‘05-574-323’ and the susceptible parent ‘02-359’. The results showed that BR resistance was controlled by a pair of additive major genes and additive-dominant multiple genes (D-2 model), and the main gene heritabilities of B1, B2, and F2 were 49.29%, 43.53%, and 50.35%, respectively. The resistant accessions obtained in this study provide new resources for cabbage BR-resistance breeding, and the inheritance analysis opens the gate for further mapping and application of the resistance gene.

Inheritance pattern of molar-incisor hypomineralization.

The aim of this study was to investigate the segregation patterns of molar incisor hypomineralization (MIH) in families, given the evidence that its etiology is influenced by genetics. Clinically, MIH may be detected in parents and/or siblings of MIH-affected children. Our study included children with at least one first permanent molar affected by MIH (proband) and their first-degree relatives (parents and siblings). The participants were examined clinically to detect MIH, according to the European Academy of Paediatric Dentistry criteria (2003). A total of 101 nuclear families (391 individuals) were studied. Proband diagnosis was followed by MIH classification of the subject, his parents and siblings, as affected, unaffected, or unknown. Segregation analysis was performed using the multivariate logistic regression model of the Statistical Analysis for Genetic Epidemiology package, and segregation models (general transmission, environmental, major gene, dominant, codominant and recessive models). The Akaike information criterion (AIC) was used to evaluate the most parsimonious model. In all, 130 affected individuals, 165 unaffected individuals, and 96 unknown individuals were studied. Severe MIH was found in 50.7% of the cases. A segregation analysis performed for MIH revealed the following different models: environmental and dominance (p = 0.05), major gene (p = 0.04), codominant (p = 0.15) and recessive models (p = 0.03). According to the AIC values, the codominant model was the most parsimonious (AIC = 308.36). Our results suggest that the codominant model could be the most likely for inheriting MIH. This result strengthens the evidence that genetic factors, such as multifactorial complex defect, influence MIH.

Genetic analysis of main flower characteristics in the F1 generation derived from intraspecific hybridization between Plumbago auriculata and Plumbago auriculata f. alba

The ornamental characteristics of Plumbago auriculata are mainly reflected in the floral organ. Exploring the genetic inheritance of flower characteristics is important for breeding new varieties. In this study, F1 segregating populations were obtained by using artificial hybridization (direct cross and reciprocal cross) between P. auriculata and its variant P. auriculata f. alba. A heterosis analysis and mixed major gene plus polygene inheritance model were used to investigate the inheritance of eight flower characteristics in the F1 generation: inflorescence length (IL), inflorescence diameter (ID), number of flowers per inflorescence (NFI), beginning of the blooming period (BBP), inflorescence number (IN), flower diameter (FD), flower length (FL) and corolla color value (CCV). In addition to the CCV, the other flower characteristics showed continuous unimodal and skewed distributions, which indicated that these characteristics were quantitative and controlled by polygenes. Although transgressive heterosis was observed only for BBP in both combinations, transgressive segregation was commonly observed, except for CCV in the F1 generation; these findings could facilitate the selection of beneficial individuals for breeding. Genetic analysis revealed that NFI could be described by a B-3 genetic model via two pairs of additive major genes; BBP could be followed by a B-2 genetic model via two pairs of additive-dominance major genes; both FL and FD could be described by a B-6 genetic model via two pairs of major genes that were equally dominant; IN was best fit by the A-1 model, which was controlled by a pair of additive-dominant-epistatic major genes; and IL and ID were best fit by the A-0 model, indicating that both characteristics were controlled by only polygenes. The heritability of the major genes controlling the NFI, BBP, FD, FL and IN traits were 92.58 %, 94.40 %, 63.42 %, 54.23 % and 65.67 %, respectively, indicating that these five characteristics were less affected by the environment. These results can provide some reference for quantitative trait locus (QTL) mapping and molecular marker-assisted breeding of the main flower characteristics in P. auriculata.

Analysis of Vitamin P Content and Inheritance Models in Eggplant

The eggplant (Solanum melongena L.) is rich in vitamin P (also known as rutin), which is beneficial for humans. In this study, the vitamin P contents of 53 eggplant lines were measured via UV spectrophotometry. The results showed that the vitamin P content differed significantly among the eggplant lines and the actual contents of vitamin P in fresh fruit pulp and fresh peel were 0.18–0.82 mg · g−1 and 0.42–2.32 mg · g−1, respectively. Furthermore, the mixed major gene and polygene inheritance model method was used for the inheritance analysis of the vitamin P content in F2 populations of three hybridization combinations. Inheritance analysis demonstrated that the vitamin P content of these eggplant lines was a quantitative trait. One or two major genes were the contributor, and the genetic effect was an additive-dominance effect. The high vitamin P content trait was regulated by the main gene and followed an additive effect. The heritability of the major genes controlling the high vitamin P content was low, while the heritability of the major gene that controls the low vitamin P content trait was high. These results provide a theoretical basis for the breeding of eggplants with high vitamin P content.

Inheritance and Quantitative Trait Locus Mapping of Fusarium Wilt Resistance in Cucumber.

Fusarium wilt (FW) is a very serious soil-borne disease worldwide, which usually results in huge yield losses in cucumber production. However, the inheritance and molecular mechanism of the response to FW are still unknown in cucumber (Cucumis sativus L.). In this study, two inbred cucumber lines Superina (P1) and Rijiecheng (P2) were used as the sensitive and resistant lines, respectively. A mixed major gene plus polygene inheritance model was used to analyze the resistance to FW in different generations of cucumber, namely, P1, P2, F1 (P1×P2), B1, and B2, obtained by backcrossing F1 plants with Superina (B1) or Rijiecheng (B2), and F2, obtained by self-crossing the F1 plants. After screening 18 genetic models, we chose the E-1 model, which included two pairs of additive-dominance-epistatic major genes and additive-dominance polygenes, as the optimal model for resistance to FW on the basis of fitness tests. The major effect quantitative trait locus (QTL) fw2.1 was detected in a 1.91-Mb-long region of chromosome 2 by bulked-segregant analysis. We used five insertion/deletion markers to fine-map the fw2.1 to a 0.60 Mb interval from 1,248,093 to 1,817,308 bp on chromosome 2 that contained 80 candidate genes. We also used the transcriptome data of Rijiecheng inoculated with Fusarium oxysporum f. sp. cucumerinum (Foc) to screen the candidate genes. Twelve differentially expressed genes were detected in fw2.1, and five of them were significantly induced by FW. The expression levels of the five genes were higher in FW-resistant Rijiecheng inoculated with Foc than in the control inoculated with water. Our results will contribute to a better understanding of the genetic basis of FW resistance in cucumber, which may help in breeding FW-resistant cucumber lines in the future.

The major gene and polygene effects of ornamental traits in bearded iris (Iris germanica) using joint segregation analysis

Bearded iris (Iris germanica) is an indispensable horticultural perennial in the garden of spring. Therefore, improving their ornamental value is of great importance in the process of breeding. In order to find out whether the inheritance of some ornamental characters in bearded iris was controlled by major genes or polygenes, the joint segregation analysis was applied to investigate the inheritance of the six characters related to ornamental values in six generations (P1, P2, F1, F2, BC1P1 and BC1P2), including plant height (PH), leaf length (LL), height of individual flower (HF), diameter of flower (DF), length of fall (LF) and width of fall (WF). The six tested characters performed large range of coefficient of variation in the offspring generations, from 8.11% to 16.48%, indicating the diversity of offspring’s phenotypic performances. The broad-sense heritability ranged from 4.55% (DF) to 51.19% (LF), suggesting the different ability to pass down these characters to the next generation. From the analysis follows the corollary that PH, HF and DF were all in accordance with the additive-dominance-epistasis major gene plus additive-dominance polygene genetic model (E-1). The optimum model for LL was the additive major gene plus additive-dominance polygene genetic model (E-3), while an additive-dominance major gene plus additive-dominance-epistasis polygene genetic model (D-0) was suitable for WF. Unlike the other five characters, LF accorded with the B-1 model, which was controlled by two major genes without polygene effect. It proved that the selection of LL and WF was more effective in early generations, while the selection of PH and DF would be more useful in late generations. This research shed some light on the inheritance pattern of ornamental characters in bearded iris, and laid solid foundation for further molecular breeding of ornamental plants.

Genetic variation and QTL mapping for cold tolerance in a chrysanthemum F1 population at different growth stages

Low temperature is a major stress factor that has adverse effects on chrysanthemum production; however, there is little information regarding the genetic mechanism of cold tolerance. Based on a previously constructed F1 mapping population, genetic variations and QTL effects were investigated for cold tolerance at the vegetative, bud, flower, and rhizome stages. The results showed that the coefficient of variation for cold tolerance at the four growth stages ranged from 22.17 to 46.14%, and heterosis and transgressive segregation were observed in both directions. Mixed inheritance model analysis revealed that cold tolerance at the vegetative and flower stages was controlled by two pairs of major genes that exhibited additivity-dominance-epistasis effects, and the heritabilities of the major genes were 88.56% and 65.86%, whereas no major gene model was identified for cold tolerance at the bud and rhizome stages. A total of 15 cold-tolerance-associated QTLs that explained 6.47–68.89% of the phenotypic variation were detected across the four stages, four of which were synergistic QTLs. Most of the identified QTLs were expressed at 2–4 growth stages, but only one QTL was identified at all four stages. This finding indicated that the QTLs underlying cold tolerance were dependent on the environment and were selectively expressed at different stages. In addition, for cold tolerance at the bud and flower stages, the QTLs qBdsCTM33 and qFfsCTM33 on the M33 linkage group accounted for 65.78% and 68.89% of the phenotypic variation, respectively, but had corresponding negative additive effects of − 5.16 and − 4.57 °C, indicating that these QTLs are major contributors to the improvement of cold tolerance. The findings of the present study reveal the genetic architecture of cold tolerance at different developmental stages, and the major QTLs and linked molecular markers identified represent an important step toward molecular-marker-assisted selection and QTL pyramiding for future breeding of cold-tolerant chrysanthemum.

Genetic analysis of tomato internode length via mixed major gene plus polygene inheritance model

Internode length is an important factor influencing tomato cultivation and breeding. To investigate the genetic inheritance of tomato internode length, a multi-generation joint analysis of major genes plus polygene model was employed in this study. Six populations (P1, P2, F1, B1, B2 and F2) were obtained from the Heinz1706 (medium internode) × P502 (long internode) and P1609 (short internode) × P502 crosses, respectively. The data of the 30th day seedlings showed that the internode length of two crosses fitted the D-2 model, followed by the one additive major gene plus additive-dominance polygene genetic model. The highest heritability of the major gene was observed in the F2 population (75.92% and 70.16%). However, the internode length of the 40th day seedlings fitted the E-1 model, namely two additive-dominance-epistasis major genes plus additive-dominance polygene genetic model. The heritabilities of the major genes ranged from 34.33% to 78.16% in B1, B2 and F2 populations, while the heritabilities of the polygene were between 1.92% and 24.50%. These results suggested that the tomato internode length was mainly controlled by major gene and should be selected in early populations. Therefore, our findings may provide important information for plant architecture modification of tomato and may lay the foundation for further QTL mapping.

Inheritance of Mesotrione Resistance in an Amaranthus tuberculatus (var. rudis) Population from Nebraska, USA.

A population of Amaranthus tuberculatus (var. rudis) evolved resistance to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor herbicides (mesotrione, tembotrione, and topramezone) in Nebraska. The level of resistance was the highest to mesotrione, and the mechanism of resistance in this population is metabolism-based likely via cytochrome P450 enzymes. The increasing number of weeds resistant to herbicides warrants studies on the ecology and evolutionary factors contributing for resistance evolution, including inheritance of resistance traits. In this study, we investigated the genetic control of mesotrione resistance in an A. tuberculatus population from Nebraska, USA. Results showed that reciprocal crosses in the F1 families exhibited nuclear inheritance, which allows pollen movement carrying herbicide resistance alleles. The mode of inheritance varied from incomplete recessive to incomplete dominance depending upon the F1 family. Observed segregation patterns for the majority of the F2 and back-cross susceptible (BC/S) families did not fit to a single major gene model. Therefore, multiple genes are likely to confer metabolism-based mesotrione resistance in this A. tuberculatus population from Nebraska. The results of this study aid to understand the genetics and inheritance of a non-target-site based mesotrione resistant A. tuberculatus population from Nebraska, USA.