Inheritance of flag-leaf angle, flag-leaf area and flag-leaf area duration in four wheat crosses

 Flag-leaf angle (FLAngle), flag-leaf area (FLarea) and flag-leaf area duration (FLADuration) are important traits in determining yield in wheat (Triticum aestivum L). Genetic studies on these traits are very few. The objective of this study was to determine the gene action controlling those traits in four wheat crosses. Six generations were available for each cross: parents (P₁ and P₂), F₁, F₂ and backcrosses (BC_(F1×P1) and BC_(F1×P2)). The joint scaling test described by Mather and Jinks was used to test goodness of fit to eight genetic models. Models including additivity, dominance and interallelic interactions best fitted the data for the three traits and the four crosses. Additive effects were most prevalent for FLAngle. They were also significant for FLArea and FLADuration. Dominance and epistatic gene action were also found, but the degree and direction was both trait- and genotype-specific. Heritabilities values were intermediate. Genetic progress, although slow, can be expected when selecting for these traits; however, selection would be most effective if delayed to later generations because of dominance and epistatic effects. Received: 20 April 1998 / Accepted: 14 July 1998     

The genetical basis of hybrid vigour in a highly heterotic cross of Nicotiana tabacum

The genetical control of F₁ heterosis, observed in a cross of desirable Nicotiana tabacum varieties, was investigated by analysing the data of the basic generations, triple test cross-families and random samples of doubled haploids (DH) and single-seed descent (SSD) lines. Analyses of the first-degree statistics revealed a complex control underlying the genetic variation, including the presence of epistasis, linkage, maternal effects and their interactions, in addition to the additive and dominance effects of the genes segregating in the cross. These analyses identified gene dispersion, directional dominance, and duplicate epistasis, as the main causes of heterosis. The triple test-cross analysis also confirmed the presence of non-allelic interactions and indicated that the dominance ratio, although inflated by epistasis, is consistently partial for all the traits. The extent of transgression in the recombinant inbred lines finally established unequivocally that, as in numerous other crosses, gene dispersion and unidirectional, but partial, dominance are the true causes of heterosis in this cross too.     

Genetic dissection of root growth in rice (Oryza sativa L.) I: a hydrophonic screen

 Root growth is an important component of the adaptation of rice to drought-prone environments. A hydroponic screen was used to study root growth of 28 rice varieties. Both maximum root length and adventitious root thickness varied widely between varieties. In general, japonica varieties had larger root systems than indica varieties. Two F₂ populations involving the thick- and long-rooted upland japonica variety ‘Azucena’ and two poor-rooting varieties, namely the upland indica‘Bala’ and the Italian japonica‘Maratelli’, were made and screened in hydroponics. Generation means analysis revealed significant additive and dominance main effects for the root length traits with a prevalence of dominance gene effects in both crosses. The dominance×dominance type of non-allelic interactions were important for maximum root length from day 7 to day 28, root volume, root thickness and root cell length in the cross ‘Bala’בAzucena’. The heritability (broad-sense) estimates varied from low to high for the traits and displayed differences between populations. This suggested that recombinant lines with improved root traits can be developed from the two crosses with selection methods that involve some form of progeny evaluation. In a companion paper, we report the mapping of quantitative trait loci (QTLs) for root growth traits in the ‘Bala’בAzucena’ population using restriction fragment length polymorphisms (RFLPs). Received: 5 May 1996 / Accepted: 14 February 1997     

Genetic investigation of contributions of embryo and endosperm genes to malt Kolbach index, alpha-amylase activity and wort nitrogen content in barley

 A genetic model is proposed for the analysis of embryo and endosperm effects as well as GE interaction effects. An investigation of three malting quality traits in grains of seven parents and their F₂s was undertaken in a half-diallel cross of barley (Hordeum distichum L.) over 2 years. The results indicated that the malt Kolbach index (KI), alpha-amylase activity (αAA) and wort soluble nitrogen (Wort-N) are controlled by both embryo genetic effects and endosperm genetic effects. Variance of the endosperm additive effects was obviously larger than that of the embryo additive effects. In the contribution of the embryo genetic effects to variation in malt αAA and Wort-N, the dominance effects were considerably larger than the additive effects. The endosperm dominance effects constituted a major part of the total genetic effect on the KI. Significant endosperm GE interactions were also detected in the malt traits concerned. Endosperm general heritability (h ² _e ) tended to be larger than interaction heritability (h ² _oE or h ² _eE ) for all the traits. Endosperm heterosis was observed to be significantly positive for αAA but negative for Wort-N in the F₂ seed generation. Prediction of main gene effects for seven parents showed that ‘Ganmu 2’ and ‘Supi1’ were suitable parental varieties for malt αAA and Wort-N improvement. Our genetic model for malting quality traits and its application in breeding are discussed. Received: 5 August 1997 / Accepted: 11 September 1997     

Single tester triple test cross analysis in spring wheat

Summary Two experiments, each including the same 30 homozygous varieties of spring wheat plus one separate tester variety, were conducted in order to detect epistasis and to test and estimate the additive and dominance components of genetic variation for five quantitative traits: final plant height, spike length, number of spikelets per spike, 100-kernel weight and grain yield per plant. Epistasis played a significant role in the control of 100-kernel weight and yield per plant. There was a gratifyingly good agreement between the two independent methods (2¯B₁i — ¯f_1i — ¯P_i and 2¯B_ci — ¯F_1i) used to test the presence of epistasis. In both experiments, there was a remarkably uniform high dominance ratio for most of the traits studied indicating that this test cross design is equally sensitive to both additive and dominance genetic variation.     

Quantitative genetics of speciation: additive and non-additive genetic differentiation between <Emphasis Type="Italic">Drosophila madeirensis</Emphasis> and <Emphasis Type="Italic">Drosophila subobscura</Emphasis>

The role of dominance and epistasis in population divergence has been an issue of much debate ever since the neoDarwinian synthesis. One of the best ways to dissect the several genetic components affecting the genetic architecture of populations is line cross analysis. Here we present a study comparing generation means of several life history-traits in two closely related Drosophila species: Drosophila subobscura, D. madeirensis as well as their F ₁ and F ₂ hybrids. This study aims to determine the relative contributions of additive and non-additive genetic parameters to the differentiation of life-history traits between these two species. The results indicate that both negative dominance and epistatic effects are very important in the differentiation of most traits. We end with considerations about the relevance of these findings for the understanding of the role of non-additive effects in speciation.     

Quantitative trait loci controlling water use efficiency and related traits in Quercus robur L.

Genetic variation for intrinsic water use efficiency (W _i) and related traits was estimated in a full-sib family of Quercus robur L. over 3 years. The genetic linkage map available for this F1 family was used to locate quantitative trait loci (QTL) for W _i, as estimated by leaf carbon stable isotope composition (δ ¹³C) or the ratio of net CO₂ assimilation rate (A) to stomatal conductance to water vapour (g _w) and related leaf traits. Gas exchange measurements were used to standardize estimates of A and g _w and to model the sensitivity of g _w to leaf-to-air vapour pressure deficit (sg^VPD). δ ¹³C varied by more than 3‰ among the siblings, which is equivalent to 40% variation of W _i. Most of the studied traits exhibited high clonal mean repeatabilities (>50%; proportion of clonal mean variability in global variance). Repeatabilities for δ ¹³C, leaf mass per area (LMA) and leaf nitrogen content were higher than 70%. For δ ¹³C, ten QTLs were detected, one of which was detected repeatedly for all 3 years and consistently explained more than 20% of measured variance. Four genomic regions were found in which co-localizing traits linked variation in W _i to variations in leaf chlorophyll and nitrogen content, LMA and sg^VPD. A positive correlation using clonal means between δ ¹³C and A/g _w, as well as a co-localisation of QTL detected for both traits, can be seen as validation of the theoretical model linking the genetic architecture of these two traits.     

Genetic control of seed weight in flax (Linum usitatissimum) and possible implications

Summary Mean seed weight data were obtained from the F₁ and F₂ of a six-by-six diallel cross with flax (Linum usita-tissimum L.). Pronounced reciprocal differences appeared in the F₁, but had largely disappeared by the F₂. The genetic control of mean seed weight was examined using two types of analysis of variance. The models underlying both analyses were fitted to the data by matrix methods supplying weighted least-squares estimates of the parameters in the models. Weights, the use of which dealt with the problem of variation in the reliability of means, were the reciprocals of the variances of individual cell (cross/self) means in the diallel data table. Elimination of redundant parameters supplied the minimum adequate models for each analysis type. Dominance was apparently masked by the large transient maternal effects in the F₁, but surfaced in the F₂, where dominance was towards larger mean seed weight. This may be coupled with findings elsewhere of possible advantages for larger seed weights to speculate on a role in preserving infrequent hybrid progeny among inbreeding (flax) species. Maternal effects producing larger seed size, plus dominance with the same result might be valuable, in conjunction with growth and competitive advantages conferred by larger seed, in preventing early elimination of rare hybrids.     

QTL and epistatic analyses of heterosis for seed yield and three yield component traits using molecular markers in rapeseed (Brassica napus L.)

Aiming to explore the basis of heterosis in rapeseed, QTLs for yield and three yield component traits were mapped and the digenic interactions were detected in an F₂ population derived from a cross between two elite rapeseed lines, SI-1300 and Eagle, in this study. Twenty-eight QTLs were detected for the four yield traits, with only two of them detected simultaneously in the Wuhan and Jingmen environments. Additive, partial dominance, dominance, and overdominance effects were all identified for the investigated traits. Dominance (including partial dominance) was shown by 55% of the QTLs, which suggests that dominance is a major genetic basis of heterosis in rapeseed. At the P ?? 0.01 level with 1000 random permutations, 108 and 104 significant digenic interactions were detected in Wuhan and Jingmen, respectively, for the four yield-related traits using all possible locus pairs of molecular markers. Digenic interactions, including additive by additive, additive by dominance, and dominance by dominance, were frequent and widespread in this population. In most cases (78.3%), the interactions occurred among marker loci for which significant effects were not detected by single-locus analysis. Some QTLs (57.1%) detected by single-locus analysis were involved in epistatic interactions. It was concluded that epistasis, along with dominance (including partial dominance), is responsible for the expression of heterosis in rapeseed.     

Quantitative genetics of bud phenology, frost damage, and winter survival in an F2 family of hybrid poplars

We studied the quantitative genetics of bud phenology, fall frost damage, and winter survival in an F₂ family (no. 822) of Populus hybrids derived from a cross between two full-sub F₁ hybrids (P. trichocarpa (Torr. & Gray×P. deltoides Bartr.). Field traits studied included the timing of bud set (BS_F) in Minnesota and Oregon, the timing of bud flush (BF_F) in Oregon, as well as fall frost damage (FD_F) and winter survival (WS_F) in Minnesota. We conclude that Family 822 has substantial genetic variability for all field traits, BS_F and BF_F are under moderate to strong genetic control (H ² _i =0.48–0.80), FD_F and WS_F are under low to moderate genetic control (H ² _i =0.27–0.40), and late bud set is associated with increased frost damage and decreased winter survival. In a warm greenhouse, we measured the timing of bud set and the number of new leaves on trees growing under either an 8-h photoperiod (BS_SD and NL_SD) or a natural photoperiod (NP) from August to December (BS_NP and NL_NP). We found that BS_SD, NL_SD, and NL_NP are under moderate genetic control (H ² _i =0.53–0.70), but the heritability of BS_NP could not be determined because few trees set bud in the warm greenhouse under the NP. By comparing results from the greenhouse experiments with results from the field, we conclude that the genetic correlation between BS_SD and BS_F (0.53–0.60) is relatively modest and that NPs in the fall are relatively ineffective at promoting bud set under warm greenhouse temperatures, although bud set readily occurred in the field. Although, low levels of light pollution in the greenhouse might have affected BS_NP, results from both greenhouse and field experiments suggest that genetic differences in photoperiodic responses play a modest role in explaining genetic differences in the timing of bud set under natural field conditions. Therefore, genetic differences in responses to other environmental factors, such as temperature, deserve greater attention. Received: 11 November 1999 / Accepted: 24 November 1999     

The genetic resolution of juvenile canopy structure and function in a three-generation pedigree of Populus

 A genetic approach to the understanding of tree architecture is to cross trees of contrasting features and to study their segregating F₂ progenies. For this purpose, members of a 3-generation pedigree, combining Populus trichocarpa, P. deltoides, and their F₁ and F₂ offspring, were grown side by side in a clonally replicated plantation. At 2 and 3 years of growth, tree architecture was analyzed at the stem, branch, and leaf levels. In all generations, proleptic branches were more numerous, longer, and had more and larger leaves than sylleptics initiated in the same year. The analysis of variance revealed significant genotypic effects on growth, branch and leaf biometrics in the F₂ family, with broad-sense heritabilities (H²) ranging from 0.50 to 0.80 for most traits. For branch and leaf traits, the H² values were found to vary among branch types and crown positions. In year 2, the degree of genetic control was stronger for sylleptics than proleptics and for upper than lower crown positions. These patterns were followed in year 3, except that H² values were more a function of position within crown, as a consequence of increased competition among trees. The genetic correlations between branch/leaf morphology and stem growth were also a function of branch type and crown position. Generally, traits on proleptics or at upper positions were more tightly correlated with height growth, whereas those on sylleptics or at lower positions, with basal area growth. By year 3, proleptic traits showed increased genetic correlations with both height and radial growth. The implications of these results for the construction of ideotypes are discussed. Received: 1 December 1995     

Cold Tolerance of the Photosynthetic Apparatus: Pleiotropic Relationship between Photosynthetic Performance and Specific Leaf Area of Maize Seedlings

The objective of this study was to elucidate the genetic relationship between the specific leaf area (SLA) and the photosynthetic performance of maize (Zea mays L.) as dependent on growth temperature. Three sets of genotypes: (i) 19 S₅ inbred lines, divergently selected for high or low operating efficiency of photosystem II (Φ_PSII) at low temperature, (ii) a population of 226 F_2:3 families from the cross of ETH-DL3 × ETH-DH7, and (iii) a population of 168 F_2:4 families from the cross of Lo964 × Lo1016 were tested at low (15/13 °C day/night) or at optimal (25/22 °C day/night) temperature. The latter cross was originally developed to study QTLs for root traits. At 15/13 °C the groups of S₅ inbred lines selected for high or low Φ_PSII differed significantly for all the measured traits, while at optimal temperature the groups differed only with regard to leaf greenness (SPAD). At low temperature, the SLA of these inbred lines was negatively correlated with Φ_PSII (r = − 0.56, p < 0.05) and SPAD (r = − 0.80, p < 0.001). This negative relationship was confirmed by mapping quantitative trait loci (QTL) in the two mapping populations. A co-location of three QTLs for SLA with QTLs for photosynthesis-related traits was detected in both populations at 15/13 °C, while co-location was not detected at 25/22 °C. The co-selection of SLA and Φ_PSII in the inbred lines and the co-location of QTL for SLA, SPAD, and Φ_PSII at 15/13 °C in the QTL populations strongly supports pleiotropy. There was no evidence that selecting for high Φ_PSII at low temperature leads to a constitutively altered SLA.     

A 9 × 9 diallel analysis in peanuts (A. hypogaea L.): Flowering time,tops' weight,pod yield per plant and pod weight

Summary Four quantitative traits were studied by analysing F₂ data derived from a 9 × 9 diallel cross utilizing widely divergent, inbred, erect cultivars of peanuts, A. hypogaea. Bidirectional dominance was found in the traits total pod yield per plant and number of days from planting to first flower; in pod size, the alleles giving small pods were consistently dominant and for high tops' weight, dominance and overdominance were found. The high heritability of pod yield/plant (0.79) indicates that breeding for higher yield/plant can succeed if large F₂ populations are grown and rigorous visual selection combined with progeny testing are employed. The genetic correlations of pod yield/plant with other traits were low. Breeding for plants with large (jumbo) pods can be aided by the fact that they are homozygous recessive, or nearly so. Simultaneous breeding for high yields and large pods is possible: there was a positive (but low) genetic correlation between the two (0.16). A modification by which less biased estimates of the number of effective factors can be obtained and a possible relationship between bidirectional dominance and genic interaction were proposed.     

Intensity of nitrification in soil as a function of time and soil moisture

Proceeding from three previously derived expressions for the intensity of nitrification in soil as a function of time (logΣN=K.logt+q), as a function of incubation moisture (logΣN=A.pF _i+B), as a function of initial moisture (logΣN=C.pF _v+D), it was shown that the nitrification intensity as a function of time and of moisture can be expressed by the bilinear function log ΣN=a.pF _i.logT+b.pF _i+c.logt+d; as a function of time and of initial moisture by the bilinear function logΣ=N=a.pF _v.logt+b.pF _v+c.logt+d; as a function of initial and incubation moisture by the bilinear function log ΣN=a.pF _ipF _v+b.pF _i+c.pF _v+d. The intensity of nitrification as a function of time, incubation moisture and initial moisture may be expressed by the multilinear function log ΣN=a.pF _i.pF _v.logt+b.pF _i.pF _v+c.pF _i.logt+d.pF _v.logt+e .pF _i+f.pF _v=g.logt+h. This function is valid for all the incubation moistures lying between pF _i 3.0 and 4.0 and for all initial moistures between 3.5 and 5.9 provided that the incubation temperature remains constant.     

QTL analysis of leaf morphology in tetraploid Gossypium (cotton)

Molecular markers were used to map and characterize quantitative trait loci (QTLs) determining cotton leaf morphology and other traits, in 180 F₂ plants from an interspecific cross between a Gossypium hirsutum genotype carrying four morphological mutants, and a wild-type Gossypium barbadense. The prominent effects of a single region of chromosome 15, presumably the classical ”Okra-leaf” locus, were modified by QTLs on several other chromosomes affecting leaf size and shape. For most traits, each parent contained some alleles with positive effects and others with negative effects, suggesting a large potential for adapting leaf size and shape to the needs of particular production regimes. Twenty one QTLs/loci were found for the morphological traits at LOD≥3.0 and P≤0.001, among which 14 (63.6%) mapped to D-subgenome chromosomes. Forty one more possible QTLs/loci were suggested with 2.0≤LOD<3.0 and 0.001<P≤0.01. Among all of the 62 possible QTLs (found at LOD≥2.0 and P≤0.01) for the 14 morphological traits in this study, 38 (61.3%) mapped to D-subgenome chromosomes. This reinforces the findings of several other studies in suggesting that the D-subgenome of tetraploid cotton has been subject to a relatively greater rate of evolution than the A-subgenome, subsequent to polyploid formation. Received: 26 April 1999 / Accepted: 30 July 1999     

Genetic analysis of frost hardiness traits in tuber-bearingSolanum species

The inheritance of frost hardiness and cold acclimation potential traits was studied in three segregating populations derived from a cross betweenSolanum commersonii Dun. PI 243503 (cmm) andSolanum cardiophyllum Lindl., PI 184762 (cph), two parental genotypes with contrasting frost hardiness and cold acclimation potential. The levels of frost hardiness and cold acclimation potential were expressed as the LT₅₀, the temperature at which 50% of the cells in leaf discs were killed, as measured by the ion leakage method, following a controlled freeze test There was considerable variation in both frost hardiness and cold acclimation potential in all three segregating populations (F₁ F₁ xcmm, and F₁ xcph). Frost hardiness and cold acclimation potential were not correlated, suggesting that these two traits are under independent genetic control. The analysis of generation means indicated that the variation for both traits could be best explained by an additive-dominance model, with additive gene effects the most important Broad-sense heritability was 0.73 and 0.74 in the F₁ population, for frost hardiness and cold acclimation potential, respectively, and was 0.85 for either trait in the F₁ xcmm population, indicating that these two traits are highly inheritable. Our results suggest that it should be possible to incorporate the frost hardiness and cold acclimation traits from S.commersonii into cultivated potato species.     

Detection of quantitative trait loci on chromosome 5R of rye (Secale cereale L.)

 Progenies of an F₂ mapping population were analyzed for quantitative traits to detect QTLs by using marker information from F₂ plants for chromosome 5R. The mapping population was segregating for the major dwarfing gene Ddw1 and the gene Hp1 for hairy peduncle. The only QTL determining plant height was located between HP1 and Ddw1 on the distal part of chromosome 5RL. At the same position a QTL for peduncle length was found, and this trait was closely related to plant height (r=0.895). Since Hp1 and Ddw1 are dominant marker loci, no dominance effect could be estimated. The QTLs for spike length and the number of florets were located near the centromere on 5RL. These two traits were correlated with r=0.824 and showed partial dominance, but these traits were not correlated to plant height and peduncle length. Homoeologous relationships between the QTLs mapped for the first time in rye and those mapped in other Triticeae members are discussed. Received: 8 June 1998 / Accepted: 8 October 1998     

Pepper morphological traits related with resistance to Phytophthora capsici

Inheritance of 10 morphological and quantitative traits related to plant and fruit development and resistance to the pathogen Phytophthora capsici was studied in an intraspecific cross between a non-pungent, susceptible Capsicum annuum parent (cv. Americano) and a wild, pungent and resistant line (Serrano Criollo de Morelos-334). Data were obtained from the segregation of 166 F₂ plants and 50 F₃ plants in four years. Three of the traits analyzed (necrosis length, leaf width and leaf length) exhibited a transgressive segregation. A multiple linear regression analysis was applied in order to establish a relationship between necrosis length and some of the morphological traits measured such as length and width of leaf, length, diameter and mass of fruit, capsaicin content in fruits, and presence of hair on leaves and stems. The results identified a linear dependence between necrosis length (as an inverse measurement of resistance) and leaf width, fruit diameter and hair presence in the stem. Pungency was not related with resistance.     

Cotton chromosome substitution lines crossed with cultivars: genetic model evaluation and seed trait analyses

Seed from upland cotton, Gossypium hirsutum L., provides a desirable and important nutrition profile. In this study, several seed traits (protein content, oil content, seed hull fiber content, seed index, seed volume, embryo percentage) for F₃ hybrids of 13 cotton chromosome substitution lines crossed with five elite cultivars over four environments were evaluated. Oil and protein were expressed both as percentage of total seed weight and as an index which is the grams of product/100 seeds. An additive and dominance (AD) genetic model with cytoplasmic effects was designed, assessed by simulations, and employed to analyze these seed traits. Simulated results showed that this model was sufficient for analyzing the data structure with F₃ and parents in multiple environments without replications. Significant cytoplasmic effects were detected for seed oil content, oil index, seed index, seed volume, and seed embryo percentage. Additive effects were significant for protein content, fiber content, protein index, oil index, fiber index, seed index, seed volume, and embryo percentage. Dominance effects were significant for oil content, oil index, seed index, and seed volume. Cytoplasmic and additive effects for parents and dominance effects in homozygous and heterozygous forms were predicted. Favorable genetic effects were predicted in this study and the results provided evidence that these seed traits can be genetically improved. In addition, chromosome associations with AD effects were detected and discussed in this study.     

Effect of gamma radiation on mutant induction of <Emphasis Type="Italic">Fagopyrum dibotrys</Emphasis> Hara

Agronomic traits, photosynthetic pigments, gas exchange, and chlorophyll (Chl) fluorescence parameters of red stem buckwheat (Fagopyrum dibotrys Hara) mutants induced by γ-radiation were compared with green control at seedling stage. Plant height, number of first-class branches, and rhizome biomass were inhibited significantly (p<0.01). Chl a, Chl b, and Chl a+b contents decreased with elevated dose of γ-rays, while increasing carotenoid content indicated that buckwheat was capable of adjusting to the radiation damage. Decrease in net photosynthetic rate was the result of both stomatal and non-stomatal limitations. Fluorescence parameters, such as F₀, F_m, F_v/F_m, F_v/F₀, Φ_PS2, electron transport rate, and photochemical quenching declined significantly (p<0.01) as compared with control due to photoinhibition, while non-photochemical quenching increased to enhance thermal dissipation. Lower parameters implied that leaf tissue was damaged significantly by high dose of γ-radiation and therefore leaf senescence was accelerated.