Population-based diallel analyses among nine historically recognized alfalfa germplasms

Identification of heterotic groups and patterns among breeding populations provides fundamental information to help plant breeders more knowledgeably manipulate heterosis. A diallel analysis was conducted among nine alfalfa (Medicago sativa L.) germplasms, commonly referred to as African, Chilean, Flemish, Indian, Ladak, M. falcata, M. varia, Peruvian, and Turkistan, which represent a significant proportion of the genetic diversity present in US cultivars. Heterotic responses were determined by evaluating forage yield of the germplasms and their 36 half-diallel hybrids in seeded plots that were harvested five times in each of 2 years. Commercially acceptable yields were obtained from some hybrids of unimproved parents, where at least one parent was adapted to the study environment. Variation among crosses was attributed primarily to general combining ability (GCA) effects; however, specific combining ability effects were also significant. GCA estimates for African, Chilean and Peruvian were positive, while those for Ladak, M. falcata, and M. varia were negative. Estimates for variety heterosis effects were positive for Peruvian and M. falcata and negative for Indian and M. varia. Significant mid-parent heterosis [(MPH) range of –21% to 55%] and high-parent heterosis [(HPH) range of –33% to 23%] was detected. M. falcata hybrids exhibited the highest MPH values. However, this likely reflects the poor yield of M. falcata per se in the study environment and consequently, low MPH values. Peruvian hybrids demonstrated the highest cross mean performance, significant positive MPH in all crosses, and positive HPH in five out of eight crosses. The results indicate that Peruvian should be recognized as a heterotic group. Alfalfa breeders may wish to explore opportunities for heterotic yield gains that are likely to exist in hybrids between the Peruvian germplasm and elite breeding populations, in particular, those adapted to the southwestern United States. MPH results suggest that alfalfa breeders may have capitalized on the heterotic response between Flemish and M. varia during past development of alfalfa synthetics adapted to the central and northern latitudes of the United States.     

Genetic relationship among bacteria classified as vibrios

Genetic relatedness among six bacterial strains currently classified as vibrios was determined by biochemical tests, deoxyribonucleic acid base composition analysis, and the detection of nucleic acid homology by the membrane filter method. Varying degrees of genetic homology existed among vibrios having similar base compositions. The bovine isolate which had a substantially different per cent guanine plus cytosine content was shown to be genetically different from the remaining vibrio strains. The use of nucleic acid homology studies in classifying vibrio strains is discussed.     

Serial analysis of combining ability in diallel and fractional diallel crosses in linseed

Summary An analysis of the nature of the gene action for seven characters influencing productivity and wide adaptation in Linum usitatissimum L. was undertaken in this investigation over three seasons based on diallel and fractional diallel crosses, among a set of ten genetically diverse parents. Estimation of combining ability and the nature of geno-type-environment interactions for the above characters was also examined.A comparison of the means of the parents and hybrids over three environments showed positive heterosis for height, number of tillers, fruit-bearing branches and capsules per plant while negative heterosis was observed for flowering time. The remaining two characters viz., height at branching and seeds per five capsules showed little differences due to mutual cancellation of the components of heterosis.A serial analysis of combining ability over three seasons using Griffing's model (1956) has revealed significant sea-sonal effects on the estimates of combining ability effects. Additive gene action was found to be predominant in most of the characters although non-additive variation due to s.c.a. was equally prominent for fruit-bearing branches and capsules per plant. On the basis of g.c.a. for all the characters, M. 10 and N. 55, both Peninsular types were the best followed by N.P. (R.R.) 45 and Mohaba Local.In the fractional diallel analysis the relative estimates g.c.a. and s.c.a. were similar for s=9 and 7. However, there was overestimation in favour of s.c.a. when s was reduced to 3. The serial analysis of fractional diallel had confirmed the results of full diallel. Significant genotype x environment interactions for flowering time, height, height at branching, fruit-bearing branches and capsules per plant were observed in this analysis also. The results have indicated that reduction of the diallel to a fraction with s=n/2 would vitiate the order and precision of estimates of combining ability.The analysis of genotype x environment indicated that the pattern of interactions among the parents of different geographical groups was not similar but varied with the character under study. Considerable interactions were observed for capsules per plant, fruit-bearing branches and flowering time in that order respectively. A comparison of the parental and hybrid populations for the degree of interaction for all the characters had revealed that heterozygosis might not at all be directly related to the degree of homeostasis. Actually, heterozygotes were found to show more interactions than homozygotes for flowering time, height at branching and tiller number and lower interactions for the other four characters. Significant seasonal effect on the degree of heterosis for vegetative as well as reproductive characters was observed in a majority of F₁'s with variable degree of dominance.

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Zusammenfassung Über einen Zeitraum von drei Vegetationsperioden wurde mit einem Material von 10 genetisch verschiedenen Eltern anhand von vollständigen und unvollständigen Diallelkreuzungen die Genwirkung bei 7 die Ertrags- und Anpassungsfähigkeit von Linum usitatissimum L. beeinflussenden Merkmalen geprüft. Außerdem wurde die Kombinationseignung dieser Merkmale und die Genotyp-Umwelt-Interaktion untersucht.Ein Vergleich der Durchschnittswerte der Eltern und Hybriden an drei verschiedenen Anbauorten ergab positive Heterosis bezüglich der Merkmale Höhe, Anzahl der Triebe, samentragende Zweige und Kapseln je Pflanze, negative Heterosis wurde dagegen bezüglich des Merkmals Blütezeit beobachtet. Die restlichen zwei Merkmale, Höhe der Verzweigung und Samenansatz von je 5 Kapseln, zeigten infolge gegenseitiger Aufhebung der Heterosiskomponenten geringe Unterschiede.Eine dreijährige Reihenanalyse hinsichtlich der Kombinationseignung nach dem Modell von Griffing (1956) ergab einen signifikanten Einfluß des Anbaujahres auf die Schätzung der Kombinationseignung. Bei den meisten Merkmalen konnte auf additive Wirkung der Gene geschlossen werden, obgleich nichtadditive Wirkung als Folge von spezieller Kombinationseignung bei den Merkmalen fruchtende Sprosse und Kapseln je Pflanze ebenso ausgeprägt war. Hinsichtlich der allgemeinen Kombinationseignung für alle untersuchten Merkmale erwiesen sich die beiden Halbinsel-Sippen, M 10 und N 55, als die besten, gefolgt von P.P. (R.R.) 45 und Mohaba Local.In den unvollständigen diallelen Analysen waren die relativen Schätzungen für allgemeine und spezielle Kombinationseignung für s=9 und 7 ähnlich. Wenn s jedoch auf 3 reduziert wurde, ergab sich eine Überschätzung der speziellen Kombinationseignung. Die Reihenanalysen des unvollständigen DiallelVersuchs bestätigten die Ergebnisse des vollständigen Diallel-Versuchs. Auch in diesem Fall wurden signifikante Genotyp-Umwelt-Interaktionen bezüglich Blütezeit, Höhe, Verzweigungshöhe, fruchtende Sprosse und Kapseln je Pflanze beobachtet. Die Ergebnisse deuteten an, daß eine Verringerung des Diallel-Versuchs auf einen Teil mit s=n/2 die Reihenfolge und Genauigkeit der Schätzung der Kombinationseignung beeinträchtigen würde.Die Analyse der Genotyp-Umwelt-Interaktion zeigte, daß die Art der Interaktion bei den Eltern verschiedener geographischer Gruppen nicht gleich war, sondern je nach dem untersuchten Merkmal variierte. Beträchtliche Interaktionen wurden für die Merkmale Kapseln je Pflanze, fruchtende Sprosse und Blütezeit — in dieser Reihenfolge — beobachtet. Ein Vergleich der Eltern- und Hybridenpopulationen bezüglich des Grades der Interaktion hat bei allen Merkmalen ergeben, daß Heterozygotie durchaus nicht unmittelbar mit dem Grad der Homeostasis in Beziehung zu stehen braucht. Tatsächlich wurde gefunden, daß Heterozygote bezüglich Blütezeit, Verzweigungshöhe und Zahl der Triebe größere Interaktionen und für die anderen 4 Merkmale geringere Interaktionen als Homozygote zeigen. Bei der Mehrzahl der F ₁-Nachkommen wurde sowohl für die vegetativen wie reproduktiven Eigenschaften ein signifikanter Einfluß des Anbaujahres mit verschiedenem Dominanzgrad auf den Grad der Heterosis beobachtet.

     

On measures of association among genetic variables

Systems involving many variables are important in population and quantitative genetics, for example, in multi-trait prediction of breeding values and in exploration of multi-locus associations. We studied departures of the joint distribution of sets of genetic variables from independence. New measures of association based on notions of statistical distance between distributions are presented. These are more general than correlations, which are pairwise measures, and lack a clear interpretation beyond the bivariate normal distribution. Our measures are based on logarithmic (Kullback-Leibler) and on relative 'distances' between distributions. Indexes of association are developed and illustrated for quantitative genetics settings in which the joint distribution of the variables is either multivariate normal or multivariate-t, and we show how the indexes can be used to study linkage disequilibrium in a two-locus system with multiple alleles and present applications to systems of correlated beta distributions. Two multivariate beta and multivariate beta-binomial processes are examined, and new distributions are introduced: the GMS-Sarmanov multivariate beta and its beta-binomial counterpart.     

Mapping quantitative trait loci controlling silking date in a diallel cross among four lines of maize

 We describe and apply an interval mapping method for quantitative trait locus (QTL) detection using F₃ and testcross progenies derived from F₂ populations obtained from a diallel cross among four elite lines of maize. Linear model-based procedures were used for the test and estimation of putative QTL effects together with genetic interactions including epistasis. We mapped QTL associated with silking date and explored their genetic effects. Ten QTL were detected, and these explained more than 40% of the phenotypic variance. Most of these QTL had consistent and stable effects among genetic backgrounds and did not show significant epistasis. QTL-by-environment interaction was important for four QTL and was essentially due to changes in magnitude of allelic effects. These results show the efficiency of our method in several genetic situations as well as the power of the diallel design in detecting QTL simultaneously over several populations. Received: 2 September 1996 / Accepted: 20 December 1996     

Asymptotically efficient partial diallel crosses

Summary The asymptotic efficiency of partial diallel crosses is defined, and circulant plans having such a property are identified. In the absence of an optimal plan to suit his requirements, the breeder should opt for suggested plans to derive maximum information for given resources.     

Production of and sensitivity to colicins among serologically classified strains of Escherichia coli

A significant proportion of 242 serologically classified strains of Escherichia coli of human origin produced colicins (33%) or were inhibited by one or more of six standard colicins (57%). The most common colicins identified were E1, I, and B; colicins B and V had greatest range of activity. Generally, neither the production of, nor sensitivity to, individual colicins was restricted to strains of a single serogroup. The coexistence of strains of one serogroup that were sensitive to the action of a colicin produced by strains of another serogroup was encountered among 2 of 21 fecal specimens containing strains of multiple serogroups. The production of colicins was not a major determinant in the acquistion of, or subsequent changes in, strains of E. coli in the feces of 10 newborn infants.