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.

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.

Connected populations for detecting quantitative trait loci and testing for epistasis: an application in maize.

Quantitative trait loci (QTL) detection experiments have often been restricted to large biallelic populations. Use of connected multiparental crosses has been proposed to increase the genetic variability addressed and to test for epistatic interactions between QTL and the genetic background. We present here the results of a QTL detection performed on six connected F(2) populations of 150 F(2:3) families each, derived from four maize inbreds and evaluated for three traits of agronomic interest. The QTL detection was carried out by composite interval mapping on each population separately, then on the global design either by taking into account the connections between populations or not. Epistatic interactions between loci and with the genetic background were tested. Taking into account the connections between populations increased the number of QTL detected and the accuracy of QTL position estimates. We detected many epistatic interactions, particularly for grain yield QTL (R(2) increase of 9.6%). Use of connections for the QTL detection also allowed a global ranking of alleles at each QTL. Allelic relationships and epistasis both contribute to the lack of consistency for QTL positions observed among populations, in addition to the limited power of the tests. The potential benefit of assembling favorable alleles by marker-assisted selection are discussed.

[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.

Doubled haploid versus S1 family recurrent selection for testcross performance in a maize population.

Theoretically, in a recurrent selection program, the use of doubled haploids (DH) can increase genetic advance per unit of time. To evaluate the efficiency expected from the use of DH for the improvement of grain yield in a maize (Zea mays L.) population, two recurrent selection programs for testcross performance were initiated using testcross progenies from DH lines and S1 families. In 4 years one selection cycle using DH and two selection cycles using S1 families were carried out with the same selection intensity for both methods. As expected, testcross genetic variance was twice as high among DH lines as among S1 families. The predicted genetic gain was 8.2% for the DH selection cycle, and 10.6% for the two S1 selection cycles, giving a per year advantage of 29% for the S1 family method over the DH method with a cycle of 4 years. With a 3-year cycle for the DH method, both methods were expected to be equivalent. Using a tester related to the one used for selection, the genetic gains obtained were equivalent for both methods: 6.6% for the DH cycle and 7.0% for the two S1 cycles. With a 3-year cycle for the DH method, the advantage would have been in favor of DH method. Furthermore, the DH method has the advantage of simultaneously producing lines that are directly usable as parents of a hybrid. Thus, if the genetic advance per unit of time is evaluated at the level of developed varieties even with the same or with a lower genetic advance in population improvement, the DH method appears to be the most efficient.

An approach to the genetics of nitrogen use efficiency in maize.

To study the genetic variability and the genetic basis of nitrogen (N) use efficiency in maize, a set of recombinant inbred lines crossed with a tester was studied at low input (N-) and high input (N+) for grain yield and its components, grain protein content, and post-anthesis nitrogen uptake and remobilization. Other physiological traits, such as nitrate content, nitrate reductase, glutamine synthetase (GS), and glutamate dehydrogenase activities were studied at the level of the lines. Genotypexnitrogen (GxN) interaction was significant for yield and explained by variation in kernel number. In N-, N-uptake, the nitrogen nutrition index, and GS activity in the vegetative stage were positively correlated with grain yield, whereas leaf senescence was negatively correlated. Whatever N-input, post-anthesis N-uptake was highly negatively related to N-remobilization. As a whole, genetic variability was expressed differently in N+ and N-. This was confirmed by the detection of QTLs. More QTLs were detected in N+ than in N- for traits of vegetative development, N-uptake, and grain yield and its components, whereas it was the reverse for grain protein content and N-utilization efficiency. Several coincidences between genes encoding for enzymes of N metabolism and QTLs for the traits studied were observed. In particular, coincidences in three chromosome regions of QTLs for yield and N-remobilization, QTLs for GS activity and a gene encoding cytosolic GS were observed. This may have a physiological meaning. The GS locus on chromosome 5 appears to be a good candidate gene which can, at least partially, explain the variation in nitrogen use efficiency.

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.

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 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 percent) presented with meconium stained (MS) amniotic fluid, of which 595 (94 percent) received bacteriological screening at birth (light MS, n=543; thick MS, n=52). Thirty (5 percent) of MS newborn had a bacteraemia (n=13, group B streptococcus, GBS), and 128 (21.5 percent) a bacterial positive gastric aspirate (n=54, GBS). Sixty-six newborns among MS babies needed tracheal suctioning (11 percent) in the delivery room for meconium inhalation. Among these 595 screening MS newborn, 286 (48 percent) presented clinical signs of postmaturity of birth, having therefore an explanation for their MS condition. For the other MS newborn 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 factros for neonatal sepsis such as intrapartum fever and prolonged rupture of membranes.(Au)

Towards a better understanding of the genetic and physiological basis for nitrogen use efficiency in maize.

To enhance our understanding of the genetic basis of nitrogen use efficiency in maize (Zea mays), we have developed a quantitative genetic approach by associating metabolic functions and agronomic traits to DNA markers. In this study, leaves of vegetative recombinant inbred lines of maize, already assessed for their agronomic performance, were analyzed for physiological traits such as nitrate content, nitrate reductase (NR), and glutamine synthetase (GS) activities. A significant genotypic variation was found for these traits and a positive correlation was observed between nitrate content, GS activity and yield, and its components. NR activity, on the other hand, was negatively correlated. These results suggest that increased productivity in maize genotypes was due to their ability to accumulate nitrate in their leaves during vegetative growth and to efficiently remobilize this stored nitrogen during grain filling. Quantitative trait loci (QTL) for various agronomic and physiological traits were searched for and located on the genetic map of maize. Coincidences of QTL for yield and its components with genes encoding cytosolic GS and the corresponding enzyme activity were detected. In particular, it appears that the GS locus on chromosome 5 is a good candidate gene that can, at least partially, explain variations in yield or kernel weight. Because at this locus coincidences of QTLs for grain yield, GS, NR activity, and nitrate content were also observed, we hypothesize that leaf nitrate accumulation and the reactions catalyzed by NR and GS are coregulated and represent key elements controlling nitrogen use efficiency in maize.

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.

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 the results, and try to identify possible necessary modifications to the existing protocol. Although more than 90 percent of women had at least one bacterial screening (vaginal or urinary) during the last trimester of pregnancy, approximately 75 percent of mothers who were heavily colonized group B streptococcus (GSB) at delivery were not detected by this systematic screening. As is also reported in other tropical areas where a great portion of nenonatal sepsis occurs in term babies, low birthweight was not a specific risk factor in this study when controlling for other major risk factor such as fever and premature rupture of membranes. Intrapartum chemoprophlaxis was associated wiyh an approximate three fold 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 chemopropylaxis as it accounted for the majority of neonatal bacteraemia that escaped the existing protocol. (AU)

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-Ó-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 I: Major risk factors of 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-a-Pitre, Guadeloupe, during a 30 month period. Group B Streptococcus (GBS) was the most common pathogen, representing 46 percent (89/194) of positive blood cultures and 52 percent (335/637) of positive gastric aspirates. Although only 3,372 (55 percent) of all live births were screened, 637 (10 percent) had gastric bacterial carriage at birth; of those, 335 (5.5 percent) involved GBS. Similarly, there were 194 (3.2 percent) positive blood cultures, of which 89 (1.5 percent) 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 percent (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.(Au)

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.

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.