Mean, genetic variance, and usefulness of selfing progenies from intra- and inter-pool crosses in faba beans (Vicia faba L.) and their prediction from parental parameters

 Determining the genetic potential of a base population from the properties of their parental lines would improve the efficiency of a breeding program. In the present study, we investigated whether the means of the parents and the genetic distance determined from RAPD data (GD) or multivariate analysis (Mahalanobis D²), mid-parent heterosis (MPH), and the absolute difference between means of the parents (∣P₁−P₂∣) can be used for predicting the means and genetic variances (σ^² _g ) of F_3:4 lines derived from different crosses in faba beans. The material comprised 18 intra- and 18 inter-pool crosses among lines from the Minor, Major, and Mediterranean germplasm pools. Fifty F_3:4 lines from each cross were evaluated for days to anthesis, plant height, seeds per plant, and seed yield in German (GE) and Mediterranean (ME) environments. GD estimates between parent lines ranged from 0.38 to 0.58, while D² ranged from 45.5 to 134.7. Correlations between means of the parents and F_3:4 lines were highly significant for most traits. Estimates of σ² _g for all traits showed non-significant correlations with MPH, GD, D². In one ME, ∣P₁−P₂∣ had significant associations with σ^² _g for seed yield and days to anthesis. The predicted usefulness of crosses, defined as the sum of the population mean and selection responses, was most closely associated with the means of F_3:4 lines. We conclude from this study that the means of F_3:4 lines can be predicted from the means of the parents, whereas the prediction of genetic variance is still an unsolved problem Received: 12 December 1997 / Accepted: 13 July 1998     

RFLP analyses of early-maturing European maize germ plasm

Summary Thirty inbred lines representing a wide range of early-maturing European elite germ plasm of maize (Zea mays L.) were assayed for RFLPs using 203 clone-enzyme combinations (106 DNA clones with restriction enzymes EcoR1 and HindIII). The genetic materials comprised 14 flint, 12 dent, and 4 lines of miscellaneous origin. Objectives were to (1) characterize the genetic diversity for RFLPs in these materials, (2) compare the level of genetic diversity found within and between the flint and the dent heterotic groups, and (3) examine the usefulness of RFLPs for assigning inbreds to heterotic groups. All but two DNA clones yielded polymorphism with at least one restriction enzyme. A total of 82 and 121 clone-enzyme combinations gave single-banded and multiple-banded RFLP patterns, respectively, with an average of 3.9 and 7.7 RFLP patterns per clone-enzyme combination across all 30 inbreds, respectively. Genetic similarity (GS) between lines, estimated from RFLP data as Dice's similarity coefficient, showed considerable variation (0.32 to 0.58) among unrelated inbreds. The mean GS for line combinations of type flint x dent (0.41) was significantly smaller than for unrelated flint lines (0.46) and dent lines (0.46), but there was considerable variation in GS estimates of individual line combinations within each group. Cluster and principal coordinate analyses based on GS values resulted in separate groupings of flint and dent lines in accordance with phylogenetic information. Positioning of lines of miscellaneous origin was generally consistent with expectations based on known breeding behavior and pedigrees. Results from this study corroborated that RFLP data can be used for assigning inbreds to heterotic groups and revealing pedigree relationships among inbreds.     

Vacuolar reticulum in oomycete hyphal tips: An additional component of the Ca2+Regulatory system?

Cultures of Achlya sp., Phytophthora cinnamomi, Saprolegnia diclina, S. ferax, and S. parasitica, treated with 6-carboxyfluorescein diacetate solution, accumulate 6-carboxyfluorescein in a reticulate system of fine tubules. The network shows longitudinal polarity within the hyphae, tubules being finest toward the hyphal tips. In more mature subapical regions the network is connected with large vacuoles that also accumulate 6-carboxyfluorescein. A morphologically similar system has also been identified in freeze-substituted hyphae of S. ferax. The network is considered to be vacuolar, but differs from the tubular vacuole system of true fungi in that tubules are less motile, more frequently branched, and do not alternate with clusters of spherical vacuoles. The appearance of the network resembles patterns of calcium-sensitive dye staining and it is suggested that the vacuolar reticulum in the tip region of oomycete hyphae may act as a Ca2+ sink. The tubular reticulum in oomycetes is very fragile and can be shown with 6-carboxyfluorescein in only those hyphal tips with a motility and organelle distribution characteristic of growing hyphae with normal morphology. Diverse abnormal hyphae show a range of other fluorochrome localizations. These include large irregular compartments filled with fluorochrome, and fluorescent cytoplasm with organelles and vacuoles standing out in negative contrast. These localizations in abnormal hyphae are correlated with other structural changes indicative of damage. Special care is required in experiments with oomycetes to avoid such artefacts of localization. Copyright 1997 Academic Press. Copyright 1997 Academic Press     

The phylogeny of some Papilio species based on interspecific hybridization data

Abstract. Adults of different species of the genus Papilio can easily be mated by hand-pairing. The data on egg hatchability, adult formation and F₁ fertility in these interspecific hybrids show notable variations according to the crosses. Using these data, values of a differentiation index for each cross were calculated. These estimates of genetic distance were then used to study the phylo-genetic relationships of the species involved. The data are consistent with the existence of the following groups, each consisting of closely related species: the black Papilio supergroup, the Papilio memnon group, the P.demoleus group, the P.xuthus group, the P.machaon group, the P.bianor group, the P.glaucus group and the P.troilus group. The phylogenetic relationships revealed by these data generally coincide with the relationships established by classical taxonomy. In cases where there are differences of opinion among taxonomists, the writer's data usually support one or other of them.     

Comparative QTL mapping of resistance to Ustilago maydis across four populations of European flint-maize

 We mapped and characterized quantitative trait loci (QTLs) for resistance to Ustilago maydis and investigated their consistency across different flint-maize populations. Four independent populations, comprising 280 F₃ lines (A×B^I), 120 F₅ lines (A×B^II), 131 F₄ lines (A×C) and 133 F₄ lines (C×D), were produced from four European elite flint inbreds (A, B, C, D) and genotyped at 89, 151, 104, and 122 RFLP marker loci, respectively. All F_n lines were evaluated in field trials with two replications in five German environments. Genotypic variances were highly significant for the percentage of U. maydis infected plants (UST) in all populations, and heritabilities exceeded 0.69. Between five and ten QTLs were detected in individual populations by composite interval mapping, explaining between 39% and 58% of the phenotypic variance. These 19 different QTLs were distributed over all ten chromosomes without any clustering on certain chromosomes. In most cases, gene action was dominant or overdominant. Fourteen pairs of the detected QTLs for UST displayed significant digenic epistatic interactions, but only two of them did so after arcsin √UST/100 transformation. Significant QTL× environment interactions occurred frequently. Between two to four QTLs were common between pairs of populations. Population C×D was also grown in Chartres, a location with a high U. maydis incidence. Two out of six QTLs identified for Chartres were in common with QTLs detected across five German environments for C×D. Consequently, marker-assisted or phenotypic selection based on results from natural infection seem to be suitable breeding strategies for improving the resistance of maize to U. maydis. Received: 3 July 1998 / Accepted: 24 July 1998     

Multi-trait association mapping in sugar beet (<Emphasis Type="Italic">Beta vulgaris</Emphasis> L.)

Association mapping promises to overcome the limitations of linkage mapping methods. The main objective of this study was to examine the applicability of multivariate association mapping with an empirical data set of sugar beet. A total of 111 diploid sugar beet inbreds was selected from the seed parent heterotic pool to represent a broad diversity with respect to sugar content (SC). The inbreds were genotyped with 26 simple sequence repeat markers chosen according to their map positions in proximity to previously identified quantitative trait loci for SC. For SC and beet yield (BY), the genotypic variances were highly significant (P < 0.01). Based on the global test of the bivariate mixed-model approach, four markers were significantly associated with SC, BY, or both at a false discovery rate of 0.025. All four markers were significantly (P < 0.05) associated with BY but only two with SC. The identification of markers associated with SC, BY, or both indicated that association mapping can be successfully applied in a sugar beet breeding context for detection of marker-phenotype associations. Furthermore, based on our results multivariate association mapping can be recommended as a promising tool to discriminate with a high mapping resolution between pleiotropy and linkage as reasons for co-localization of marker-phenotype associations for different traits.     

QTL mapping for resistance against the European corn borer (Ostrinia nubilalis H.) in early maturing European dent germplasm

The European corn borer (ECB, Ostrinia nubilalis Hübner) is a major pest of maize in Central Europe. We mapped and characterized quantitative trait loci (QTLs) involved in resistance of maize against ECB damage, compared them with QTLs for agronomic traits, and evaluated the usefulness of marker-assisted selection (MAS) for improving ECB resistance in early maturing European maize germplasm. A total 226 F₃ families from the cross D06 (resistant) × D408 (susceptible), together with 93 RFLP and two SSR markers were used for the QTL analyses. For each F₃ family we measured the length of tunnels produced by larval stalk mining (TL), stalk damage ratings (SDR), and relative grain yield (RGY) in field experiments, with two replications in two environments in 1 year. The agronomic traits comprised grain yield under insecticide protection (GYP) and manual ECB larval infestation (GYI), the date of anthesis (ANT), and the in vitro digestibility of organic matter (IVDOM) of stover. Estimates of genotypic variance (σ² _g) were highly significant for all traits. Six QTLs for TL and five QTLs for SDR were detected, explaining about 50.0% of σ² _g. Most QTLs showed additive gene action for TL and dominance for SDR. No QTL was found for RGY. The number of QTLs detected for the agronomic traits ranged from two for GYI to 12 for ANT, explaining 12.5 to 57.3% of σ² _g, respectively. Only a single QTL was in common between the two resistance traits, as expected from the moderate trait correlation and the moderate proportions of σ² _g explained. Based on these results, MAS for improving ECB resistance can be competitive when cost-effective PCR-based marker systems are applied. However, it remains to be established whether the putative QTL regions for ECB resistance detected in the population D06 × D408 are consistent across other early maturing European maize germplasms. Received: 20 December 1999 / Accepted: 6 June 2000     

A reassessment of decreased amino acid accumulation by ehrlich ascites tumor cells in the presence of metabolic inhibitors

This study was undertaken to examine the mechanism by which metabolic inhibition reduces amino acid active transport in ehrlich ascites tumor cells. At 37 degrees C the metabolic inhibitor combination 0.1 mM 2,4-dinitrophenol (DNP) + 10 mM 2- deoxy-D-glucose (DOG) reduced the cell ATP concentration to 0.10- 0.15 mM in less than 5 min. This inhibition was associated with a 20.6 percent +/- 6.4 percent (SD) decrease in the initial influx of α-aminoisobutyric acid (AIB), and a two- to fourfold increase in the unidirectional efflux. These effects could be dissociated from changes in cell Na(+) or K(+) concentrations. Cells incubated to the steady state in 1.0-1.5 mM AIB showed an increased steady-state flux in the presence of DNP + DOG. Steady- state fluxes were consistent with trans-inhibition of AIB influx and trans-stimulation of efflux in control cells, but trans- stimulation of both fluxes in inhibited cells. In spite of the reduction of the cell ATP concentration to less than 0.15 mM and greatly reduced transmembrane concentration gradients of Na(+) and K(+), cells incubated to the steady state in the presence of the inhibitors still established an AIB distribution ration 13.8 +/- 2.6. The results are interpreted to indicate that a component of the reduction of AIB transport produced by metabolic inhibition is attributable to other actions in addition to the reduction of cation concentration gradients. Reduction of cell ATP alone is not responsible for the effects of metabolic inhibition, and both the transmembrane voltage and direct coupling to substrate oxidation via plasma-membrane-bound enzymes must be considered as possible energy sources for amino acid active transport.     

Variation of the parental genome contribution in segregating populations derived from biparental crosses and its relationship with heterosis of their Design III progenies

The variation of the parental genome contribution (PGC) and its relationship with the genetic architecture of heterosis have received little attention. Our objectives were to (1) derive formulas for the variance of PGC in selfing, backcross (BC) or intermated generations produced from biparental crosses of homozygous parents, (2) investigate the correlation r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) of the PGC (\Uppsi_M ) (\Uppsi_{M} ) estimated by a set M of markers, with Z ₂ (half the trait difference between each pair of BC progenies) in the Design III, and (3) interpret experimental results on this correlation with regard to the genetic basis of heterosis. Under all mating systems, the variance of PGC is smaller in species with a larger number and more uniform length of chromosomes. It decreases with intermating and backcrossing but increases under selfing. The ratio of variances of PGC in F₁DH (double haploids), F₂ and BC₁ populations is 4:2:1, but it is smaller in advanced selfing generations than expected for quantitative traits. Thus, altering the PGC by marker-assisted selection for the genetic background is more promising (i) in species with a smaller number and/or shorter chromosomes and (ii) in F₂ than in progenies of later selfing generations. The correlation r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) depends on the linkage relationships between M and the QTL influencing Z₂ as well as the augmented dominance effects d_i^* d_{i}^{*} of the QTL, which include dominance and additive × additive effects with the genetic background, and sum up to mid-parent heterosis. From estimates of r(Z₂ ,\Uppsi_M ) r(Z_{2} ,\Uppsi_{M} ) as well as QTL studies, we conclude that heterosis for grain yield in maize is caused by the action of numerous QTL distributed across the entire genome with positive d_i^* d_{i}^{*} effects.