General and specific combining abilities in a maize (Zea mays L.) test-cross hybrid panel: relative importance of population structure and genetic divergence between parents.

KEY MESSAGE: General and specific combining abilities of maize hybrids between 288 inbred lines and three tester lines were highly related to population structure and genetic distance inferred from SNP data. Many studies have attempted to provide reliable and quick methods to identify promising parental lines and combinations in hybrid breeding programs. Since the 1950s, maize germplasm has been organized into heterotic groups to facilitate the exploitation of heterosis. Molecular markers have proven efficient tools to address the organization of genetic diversity and the relationship between lines or populations. The aim of the present work was to investigate to what extent marker-based evaluations of population structure and genetic distance may account for general (GCA) and specific (SCA) combining ability components in a population composed of 800 inter and intra-heterotic group hybrids obtained by crossing 288 inbred lines and three testers. Our results illustrate a strong effect of groups identified by population structure analysis on both GCA and SCA components. Including genetic distance between parental lines of hybrids in the model leads to a significant decrease of SCA variance component and an increase in GCA variance component for all the traits. The latter suggests that this approach can be efficient to better estimate the potential combining ability of inbred lines when crossed with unrelated lines, and limits the consequences of tester choice. Significant residual GCA and SCA variance components of models taking into account structure and/or genetic distance highlight the variation available for breeding programs within structure groups.

[Management of ectopic pregnancy in developing countries: example of a Nigerian reference maternity]. / Prise en charge de la grossesse extra-utérine dans les pays en voie de développement: exemple d'une maternité de référence au Niger.

OBJECTIVE: We report 143 cases of ectopic pregnancy (EP) treated in the Issaka-Gazobi maternity of Niamey between January 1st, 1999 and April 30th, 2001 (28 months). The objective of this study was to estimate the epidemiological, diagnostic and therapeutic aspects to propose actions, which could lead to the improvement of the prognosis of EP. PATIENTS AND METHODS: The frequency of ectopic pregnancy was 2.32% in our study. The patients were young and pregnant for the second or third time. Frequently we observed previous sexually contagious infections and/or abortions. More than 70% of the patients were admitted for a complicated stage of EP. RESULTS: The culdocentesis allowed to evoke the diagnosis in more than 80% of the cases. It is a simple gesture, which makes it possible to make the diagnosis of EP and which should be taught and practised in maternities of the developing countries. The pelvic ultrasonography and the laparoscopy allowed the diagnosis in the other cases. The tubal localization was the most frequent, cervical and abdominal pregnancies were found. The surgical treatment conducted by laparotomy was conservative in 11.9% and radical in 87.4% of the cases. The mortality rate was still 0.70%. DISCUSSION AND CONCLUSION: Prevention of the sexually contagious infections and medical management of abortions are important to reduce the risks of ectopic pregnancies. Education of the patients, living far from the maternity, is also necessary to obtain more precocious consultation in case of pregnancy in order to improve the prognosis of EP.

An Analysis of Heterosis VS. Inbreeding Effects with an Autotetraploid Cross-Fertilized Plant: MEDICAGO SATIVA L.

Self-fertilization and crossing were combined to produce a large number of levels of inbreeding and of degrees of kinship. The inbreeding effect increases with the complexity of the character and with its supposed relationship with fitness. A certain amount of heterozygosity appears to be necessary for the expression of variability. With crossing of unrelated noninbred plants, genetic variance is mainly additive, but with inbreeding its major part is nonadditive. High additivity in crossing, therefore, coexists with strong inbreeding depression. However, even in inbreeding the genetic coefficient of covariation among relatives appears to be strongly and linearly related to the classical coefficient of kinship. This means that deviations from the additive model with inbreeding could be partly due to an effect of inbreeding on variances through an effect on means. An attempt to analyze genetic effects from a theoretical model, based upon the identity by descent relationship at the level of means and of covariances between relatives, tends to show that allelic interactions are more important and nonallelic interactions are less important for a character closely related to fitness. For a complex character, these results lead to the conception of a genome organized in polygenic complementary blocks integrating epistasis and dominance. Some consequences for plant breeding are also discussed.

Quantitative genetics of doubled haploid populations and application to the theory of line development.

The line value of a genotype is defined as the expected value of all lines that can be derived from this genotype. Specific genetic effects are defined for this value: only additive and additive by additive epistatic effects are necessary. There is no dominance effect for such a value. A general expression for the covariances between related lines is given. From a design with several lines per haplodiploidized plant taken at random from a population it is possible to estimate the additive variance for line value and the variance of additive by additive epistasis for line value. Variances of higher order epistasis can be estimated with a two-factor mating design in which a cross is replaced by the population of lines that can be derived from it. With a diallel or a factorial design a direct test for the presence of homozygous by homozygous epistasis is possible. The application of the concept of line value to the theory of line development leads to simple expressions of genetic advance in one cycle of recurrent selection according to the testing system. A brief consideration of these expressions leads to the conclusion that single doubled haploid descent recurrent selection will be one of the most efficient methods for low heritabilities and with a rapid development of doubled haploid lines.

Covariances between Arbitrary Relatives in Autotetraploids with Panmictic Disequilibrium.

In random mating autopolyploid populations which have not reached equilibrium, two alleles may be interdependent as a result of the phenomenon of gametic recombination, i.e. the maintenance through successive gamete generations of an association of two alleles from the same gamete in a source reference generation. Any two alleles are dependent by this relationship if they derive by descent from the same ancestral gamete in the source population. Applied with the classical notion of identity by descent, the concept thus defined identifies new coefficients of dependence between arbitrary relatives. Coefficients of dependence are probabilities attached to the drawing of genes from two zygotes such that there are certain relationships amongst them. Applying the concept to autotetraploids, consideration of the states of dependence between the genes of a zygote or of a pair of zygotes leads to the definition of new parameters bearing on population means, variances and covariances, for arbitrary inbreeding. The absence of epistasis is supposed. Some applications of interest in artificial selection are briefly envisaged, with simplifying restrictions on genetic effects. The particular case of diallelism is also considered.

Marker-assisted selection efficiency in populations of finite size.

The efficiency of marker-assisted selection (MAS) based on an index incorporating both phenotypic and molecular information is evaluated with an analytical approach that takes into account the size of the experiment. We consider the case of a population derived from a cross between two homozygous lines, which is commonly used in plant breeding, and we study the relative efficiency of MAS compared with selection based only on phenotype in the first cycle of selection. It is shown that the selection of the markers included in the index leads to an overestimation of the effects associated with these markers. Taking this bias into account, we study the influence of several parameters, including experiment size and heritability, on MAS efficiency. Even if MAS appears to be most interesting for low heritabilities, we point out the existence of an optimal heritability (approximately 0.2) below which the low power of quantitative trait loci detection and the bias caused by the selection of markers reduce the efficiency. In this situation, increasing the power of detection by using a higher probability of type I error can improve MAS efficiency. This approach, validated by simulations, gives results that are generally consistent with those previously obtained by simulations using a more sophisticated biological model than ours. Thus, though developed from a simple genetic model, our approach may be a useful tool to optimize the experimental means for more complex genetic situations.

Quantitative genetics of 4x-2x hybrid populations with first-division restitution and second-division restitution 2n gametes produced by diploid parents.

A model is proposed to describe the genetic value of 4x-2x hybrids resulting from crosses between tetraploid genitors and diploid genitors that produce 2n gametes. The model takes into account the genetic consequences of the First Division Restitution (FDR) and Second Division Restitution (SDR) meiosis, particularly on the homozygosity level that 2n gametes contribute to 4x-2x hybrids. As genes can be identical by descent, numerous parameters are needed in the classical approach to describe the inbreeding effects on the mean and variance of 4x-2x hybrids. Using the concept of test value, the model allows a large decrease in the number of required parameters. The model gives the components of genetic variance and usual covariances between relatives using these synthetic parameters. The model is then used to study the efficiency of a recurrent breeding scheme to improve diploid genitors for their combining ability with tetraploid genitors. It appears that, in presence of dominance, ignoring the meiosis pattern will lead to an overestimation of additive variance and then of genetic advance. Some genetic considerations on the differences between FDR and SDR mechanisms lead us to suggest an experimental comparison of their respective advantages and disadvantages for the type of considered recurrent selection. An experimental crossing design is proposed to obtain estimates of the genetic parameters needed for this comparison.

Intentional delayed delivery in twin pregnancy. Two additional cases and literature review.

We report two cases of retention of the second twin after delivery of the first one. Both pregnancies were bichorionic, biamniotic. In both cases the first twin was delivered during the second trimester. Tocolysis and antibiotics were used. The two pregnancies had a different outcome. For the first patient with a cerclage, the interval delivery was 67 days, allowing a gestational age of 28 weeks and a weight of 1070 g. The child is now 4 years old and has a normal development. In the second case, the second twin was delivered at 20 1/2 weeks, 8 days after the first, and died shortly after birth. Reviewing the literature, 34 twin pregnancies are reported with intentional delay delivery and 27 infants survived out of 68 fetuses. Cerclage does not seem to be essential for success. Prophylactic antibiotics and tocolysis are admitted. The main problem is infection which defines the prognosis.

Comparative study of the influence of aminoglycoside antibiotics on the activity of the horizontal semicircular canal in the frog.

This work is an electrophysiological study made in the frog. The technique allows one to test and to compare the actions of a number of aminoglycoside antibiotics, directly introduced into the labyrinthic cavity, on the spontaneous activity of a vestibular receptor--the horizontal semicircular canal. The effects of aminoglycoside solutions have been compared with those of physiological solutions (NaCl 7 g/l, Ringer) and of penicillin (not ototoxic). The results obtained show: (1) After the introduction of a physiological solution the activity disappears only very briefly (electrical artefact, probably); after a few minutes the activity returns to its initial value. A similar phenomenon is obtained with penicillin. (2) When used at a dose of 10 microgram, all the aminoglycosides studied generally induced an important and lasting decrease in semicircular canal activity. (3) These aminoglycosides have been classified according to their vestibular local toxicity. Their descending order of influence is as follows: streptomycin, dihydrostreptomycin, amikacin (BBK 8), neomycin, sisomycin, gentamicin and lividomycin, tobramycin, kanendomycin. (4) A parallel can be drawn between local vestibular toxicity and clinical ototoxicity. The role and importance of the hemolabyrinthic barrier are noted and the notion of ototoxicity is discussed.

Vestibular effects of antibiotics introduced in the inner ear. Behavioral and electrophysiological studies in the frog.

The aim of this study was to find a rapid and suitable method for testing the toxicity of drugs upon the vestibular end organs. The experiments were performed in the frog and the action of two antibiotics, streptomycin sulphate and penicillin G, was studied by carefully observing the equilibrium behaviour of the animals and recording the spontaneous activity of the nerve of the horizontal semicircular canal. The results obtained show that: 1) injection of streptomycin sulphate (20 microgram) directly into the labyrinthic cavity elicited disorders of the equilibrium and reduced the spontaneous activity of the horizontal canal nerve; 2) these disorders were reversible or not depending on the animal; 3) there is a good correlation between behavioral observations and electrophysiological data (i.e. the activity of the ampullary nerve was low in frogs whose behaviour was impaired at the time of sacrifice; the activity did not differ from controls when the normal behaviour was completely restored); 4) injection of penicillin G or 0.7% NaCl into the labyrinthic cavity had no effect on the equilibrium of the frogs or on the activity of the ampullary nerve; 5) intramuscular or intralymphatic injections of streptomycin sulphate produced a neuromuscular block but did not alter the activity of the ampullary nerve. In conclusion, the question of ototoxicity is discussed.

[Adolescence and pregnancy in Guadeloupe. 184 cases]. / Adolescence et maternité en Guadeloupe. A propos de 184 observations.

Maternal pregnancy complications and pregnancy outcomes of all adolescent pregnancies (< 18 years; n = 184) during a two year survey (1993-1994) at the Maternity of University Hospital of Pointe-á-Pitre, Guadeloupe, French West Indies, were compared to that of an older cohort (20-35 years; n = 3938). there were no statistical differences between the two groups in obstetrical complications (infections, hypertension, fetal deaths), birthweight, gestational age at delivery or apgar scores at birth. Adolescents were more likely to have mechanical extractions (forceps, vacuum) and less cesarean sections although differences were not significant. On the other hand, prenatal care was significantly poorer in adolescents. These results are in accordance with the literature. It remains that the adolescent pregnancy rate is higher in Guadeloupe as compared to Europe or mainland France. Although these data do not suggest an elevated reproductive health risk for adolescents, it does inflict a social burden of decreased potential for productivity.

Evaluation of neonatal sepsis screening in a tropical area. Part I: Major risk factors for bacterial carriage at birth in Guadeloupe.

This prospective study reports on screening for neonatal sepsis among 3,372 live births out of 6,060 consecutive deliveries at the University Hospital of Pointe-à-Pitre, Guadeloupe, during a 30-month period. Group B Streptococcus (GBS) was the most common pathogen, representing 46% (89/194) of positive blood cultures and 52% (335/637) of positive gastric aspirates. Although only 3,372 (55%) of all live births were screened, 637 (10%) had gastric bacterial carriage at birth; of those, 335 (5.5%) involved GBS. Similarly, there were 194 (3.2%) positive blood cultures, of which 89 (1.5%) involved GBS. In this report, all newborns who presented with a positive GBS blood culture had at least one of the external tests positive for GBS (gastric, ear canal, rectum and placenta). Thirty-seven per cent (14/38) of positive neonatal blood cultures occurred in newborns with foetid liquor while in deliveries with intrapartum fever 16.5% (32/195) of blood cultures were positive. In our clinical practice, characteristics that were evident in the delivery room (without knowledge of prenatal follow-up) such as foetid liquor, intrapartum fever, prolonged rupture of membranes, foetal tachycardia and meconium staining were associated with the great majority of neonatal sepsis.

Evaluation of neonatal sepsis screening in a tropical area Part III: Neonatal sepsis in meconium stained deliveries.

Of the 6,060 consecutive live births delivered at the University Maternity Unit of Guadeloupe (French West Indies) during a 30-month period, 635 newborns (10.4%) presented with meconium stained (MS) amniotic fluid, of which 595 (94%) received bacteriological screening at birth (light MS, n = 543; thick MS, n = 52). Thirty (5%) of MS newborns had a bacteraemia (n = 13, group B streptococcus, GBS), and 128 (21.5%) a bacterial positive gastric aspirate (n = 54, GBS). Sixty-six newborns among MS babies needed tracheal suctioning (11%) in the delivery room for meconium inhalation. Among these 595 screened MS newborns, 286 (48%) presented clinical signs of postmaturity at birth, having therefore an explanation for their MS condition. For the other MS newborns without the postmaturity explanation, we experienced twofold increased risk of neonatal sepsis (OR 1.88 for bacteraemia and 2.61 for external carriage p < 0.02, Chi square) as compared with their MS postmature counterparts. We conclude that when meconium stained deliveries are associated with postmaturity signs, one may not need to initiate prophylactic antibiotic treatment at birth unless they present with other traditional risk factors for neonatal sepsis such as intrapartum fever and prolonged rupture of membranes.

Evaluation of neonatal sepsis screening in a tropical area. Part II: Evaluation of intrapartum chemoprophylaxis protocol.

The authors report on an analysis of a chemoprophylaxis protocol at the University Hospital of Guadeloupe in the Caribbean. This study comprised 6,060 consecutive deliveries and was initiated to assess the application of an intrapartum chemoprophylaxis protocol, evaluate its results, and try to identify possible necessary modifications to the existing protocol. Although more than 90% of women had at least one bacterial screening (vaginal or urinary) during the last trimester of pregnancy, approximately 75% of mothers who were heavily colonized group B streptococcus (GBS) at delivery were not detected by this systematic screening. As is also reported in other tropical areas where a great proportion of neonatal sepsis occurs in term babies, low birthweight was not a specific risk factor in this study when controlling for other major risk factors such as fever and premature rupture of membranes. Intrapartum chemoprophylaxis was associated with an approximate threefold decrease in the risk of GBS neonatal bacteraemia among at risk deliveries. The results suggest that, in our tropical context, prolonged rupture of membranes of at least 12 hours' duration should be considered as a cause for intrapartum chemoprophylaxis as it accounted for the majority of cases of neonatal bacteraemia that escaped the existing protocol.

[Genital Schistosoma mansoni bilharziasis in women: apropos of 2 cases in Guadeloupe]. / Bilharziose génitale de la femme à Schistosoma mansoni: à propos de deux cas en Guadeloupe.

Schistosoma mansoni is the only cause of bilharziasis in Guadeloupe (French West Indies). Ectopic ovarian and endometrial involvement is rare with only one case of bilharziasis of the endometrium having previously been described in the literature. This report describes two cases of Schistosoma mansoni bilharziasis revealed by genital tract involvement. In one case involvement was endometrial and led to metrorrhagia. Histological examination of the biopsy sample obtained by curettage of the endometrium demonstrated the presence of eggs with lateral spurs. In the other case ovarian involvement was detected during assessment for associated infertility and chronic pelvic pain. Celioscopic examination showed pelvic and perihepatic adhesions secondary to sexually transmissible infection. Histologic examination of an ovarian growth demonstrated the presence of Bilharzia eggs. Both patients underwent antiparasitic treatment using oxamniquine (Vansil) which led to the resolution of metrorrhagia in the first case.

The genetic basis of heterosis: multiparental quantitative trait loci mapping reveals contrasted levels of apparent overdominance among traits of agronomical interest in maize (Zea mays L.).

Understanding the genetic bases underlying heterosis is a major issue in maize (Zea mays L.). We extended the North Carolina design III (NCIII) by using three populations of recombinant inbred lines derived from three parental lines belonging to different heterotic pools, crossed with each parental line to obtain nine families of hybrids. A total of 1253 hybrids were evaluated for grain moisture, silking date, plant height, and grain yield. Quantitative trait loci (QTL) mapping was carried out on the six families obtained from crosses to parental lines following the "classical" NCIII method and with a multiparental connected model on the global design, adding the three families obtained from crosses to the nonparental line. Results of the QTL detection highlighted that most of the QTL detected for grain yield displayed apparent overdominance effects and limited differences between heterozygous genotypes, whereas for grain moisture predominance of additive effects was observed. For plant height and silking date results were intermediate. Except for grain yield, most of the QTL identified showed significant additive-by-additive epistatic interactions. High correlation observed between heterosis and the heterozygosity of hybrids at markers confirms the complex genetic basis and the role of dominance in heterosis. An important proportion of QTL detected were located close to the centromeres. We hypothesized that the lower recombination in these regions favors the detection of (i) linked QTL in repulsion phase, leading to apparent overdominance for heterotic traits and (ii) linked QTL in coupling phase, reinforcing apparent additive effects of linked QTL for the other traits.

Genetic variation for N-remobilization and postsilking N-uptake in a set of maize recombinant inbred lines. 3. QTL detection and coincidences.

The objective of this study was to map and characterize QTLs for traits related to nitrogen utilization efficiency (NUE), grain N yield, N-remobilization and post-silking N-uptake. Furthermore, to examine whether QTLs detected with recombinant inbred lines (RILs) crossed to a tester are common to those detected with line per se evaluation, both types of evaluations were developed from the same set of RILs. The material was studied over two years at high N-input, and one year at low N-input. We used (15)N-labelling to evaluate with accuracy the proportion of N remobilized from stover to kernels and the proportion of postsilking N-uptake allocated to kernels. With 59 traits studied in three environments, 608 QTLs were detected. Using a method of QTL clustering, 72 clusters were identified, with few QTLs being specific to one environment or to the type of plant material (lines or testcross families). However, considering each trait separately, few QTLs were common to both line per se and testcross evaluation. This shows that genetic variability is expressed differently according to the type of progeny. Studies of coincidences among QTLs within the clusters showed an antagonism between N-remobilization and N-uptake in several QTL-clusters. QTLs for N-uptake, root system architecture and leaf greenness coincided positively in eight clusters. QTLs for remobilization mainly coincided in clusters with QTLs for leaf senescence. On the whole, sign of coincidences between QTLs underlined the role of a "stay-green" phenotype in favouring N-uptake capacity, and thus grain yield and N grain yield.

Detection of marker-QTL associations by studying change in marker frequencies with selection.

The value of selective genotyping for the detection of QTL has already been studied from a theoretical point of view but with the assumption of a negligible contribution (r2P) of the QTL to the phenotypic variance. For predicting change in gene frequency, we show that this assumption is only valid for r2P less than 0.05 and for a proportion selected higher than 1%. Therefore, we develop a study of the optimization of selective genotyping without assumption on QTL effect, with selection either of both tails (bidirectional genotyping or BSG) or only one tail (unidirectional genotyping or USG). For a given population size of phenotyped plants the optimal proportion selected for selective genotyping is around 30% for each tail. For the same investment as in ANOVA, by investing more in phenotyping than in genotyping when the cost ratio of genotyping to phenotyping is higher than 1, the optimal proportion selected appears to be between 10 and 20% for each tail. It is mainly affected by the cost ratio and decreases when the cost ratio increases. At this optimum, BSG is competitive with ANOVA, or even more powerful, when the cost ratio is higher than 1. USG can also be competitive when the cost ratio is higher than 2. Using experimental data from two populations of about 300 F4 inbred families of maize, it was verified that BSG at the optimum gives the same results as ANOVA or is better whereas USG is less powerful or equivalent.