Specific Combining Ability Values Research Articles

Capacidade combinatória entre híbridos simples de milho em dialelo circulante

Onze híbridos comerciais de milho (AS 1550, DKB 214, DKB 215, DKB 330, Dow 2B150, Dow 8460, P 30F33, P 30F53, P 30P70, Penta e Premium Flex) foram intercruzados, obtendo-se 44 híbridos duplos, segundo um dialelo circulante com p=11 (onze genitores) e s=8 (intercruzados 8 a 8), avaliado em delineamento em blocos casualizados com três repetições. Foram conduzidos dois experimentos na Região Centro-sul do Paraná, nos municípios de Guarapuava e Goioxim. Os dados referentes à produção de grãos, altura média de planta e altura média de inserção de espiga foram submetidos à análise dialélica. Houve diferenças significativas entre os locais e entre os híbridos do dialelo para as três características avaliadas. Também houve efeito significativo da interação locais x híbridos do dialelo para a produção de grãos. Houve diferenças significativas para a capacidade geral de combinação (CGC) em todas as características e para a capacidade específica de combinação (CEC) apenas na produção de grãos. Destacaram-se por sua CGC os híbridos Penta, P 30F53 e Dow 8460 na produção de grãos, o híbrido AS 1550 quanto á menor altura de planta e de inserção da espiga. A melhor combinação híbrida para a produtividade foi Penta x P 30F53, por apresentar a maior média, elevada CEC e ambos os genitores terem as maiores estimativas de CGC. O genitor P 30F53 participou de três dos quatro híbridos duplos mais produtivos. É possível a obtenção de novas populações a partir de cultivares comerciais que se destacaram por sua CGC, e que, nos cruzamentos em que participaram, houve, também, estimativas favoráveis da CEC.

Combining Ability of Yield-Component Traits for Indica Chromosome Substituted Segments in Japonica Hybrid Rice

To study the heterosis of inter-subspecies hybrid in rice ( Oryza sativa L.), 10 chromosome segment substitution lines (CSSLs) with Asominori ( japonica) background derived from Asominori × IR24 ( indica) and the parent Asominori were crossed with 6 japonica tester lines (as male parents). A total of 66 combinations were planted in the field with NCII design. The 10 CSSLs had higher general combining abilities (GCAs) than the parent Asominori in the main yield-component traits, excluding the thousand-grain weight. Five CSSLs, AIS84, AIS27, AIS3, AIS80, and AIS76 with chromosome substitution segments from chromosomes 12, 4, 1, 11, and 11, respectively, ranked as the top 5 in the GCA of yield-related characteristics. The results showed stronger heterosis in the indica/japonica combinations at the chromosome segment level than in the typical japonica hybrid rice. Intentionally substituting japonica chromosome segments with indica counterparts, such as, X24–2– R367 in chromosome 12, R1854– R288 in chromosome 4, C970– C955 in chromosome 1, C1350– R257 in chromosome 11, and X52– R2913 in chromosome 11, could significantly promote the yield potential of japonica hybrid rice. Different combinations with one identical parent or different traits in the same combination had significant differences in the specific combining ability (SCA). Combinations with the highest and lowest SCA values were derived from different parental GCA groups, indicating no causal relations between SCA and parental GCA. High GCA combined with strong SCA is a basic principle of parental selection in the breeding programs of super high-yielding hybrid rice.

Assessment of tomato source breeding material through mating designs

SUMMARYCultivated tomato has a narrow germplasm base because of several population bottlenecks in the form of founder events, as well as natural and artificial selections that occurred during domestication and evolution of modern cultivars. The F2of commercial single-cross hybrids, as well as locally well-adapted varieties, provide germplasm for developing recombinant lines and exploiting genetic variability, respectively. The present study aims to discriminate the breeding value of tomato source material, i.e. commercial hybrids or well-adapted varieties, by (i) estimating tolerance to inbreeding of hybrids or estimating heterosis of diallel hybrids between varieties, (ii) determining undesirable traits and (iii) determining general combining ability (GCA) and specific combining ability (SCA) effects from diallel crosses between hybrids and between varieties. Two hybrids and four varieties were assessed. One hybrid showed 0·03 inbreeding vigour, which was not combined with undesirable traits in the F2generation. However, negative GCA and positive SCA values did not support the hybrid as source material, provided that hybrids with low inbreeding depression, positive GCA and negative SCA correspond to an F2capable of developing recombinant lines. The assessment of the varieties showed positive GCA and 0·34 heterosis in one variety, indicating agreement between yield and GCA, and that high-yielding varieties may produce high-yielding hybrids. In conclusion, the proposed mating design, taking into account the tolerance to inbreeding for hybrids and the heritability of general worth for both resources, provides a mechanism for ensuring continued improvement in plant performance through plant selection programmes.

Heterosis, habilidad combinatoria y diversidad genética en híbridos comerciales de maíz (Zea mays L).

Knowledge about the combining ability, genetic diversity and heterosis of germoplasm from a maize breeding program is essential for hybrids and varieties development. The objetives of this study were (1) To identify commercial hybrids with high genetic value (GCA and heterosis) useful for initiating a maize breeding program to produce and improved hybrids, varieties and synthetics; (2) To demonstrate that is feasible to create a maize breeding program from commercial hybrids. Estimates of general (GCA) and specific combining ability (SCA) were obtained using the method IV of Griffing (1956) and the genetic distances were estimated according to the method suggested by Troyer (1988). The best crosses were AS910 X AS4450 and PP9538 X AS948 having a yield of 17.538 and 17.463 t/ha respectively; the same crosses had the highest values of SCA. The crosses with the highest values of heterosis over the midparent were PP9539 X AN453 and PP9603 X PP9539 with 11,35 and 11,13 percent respectively. The highest positive values of GCA effects were obtained from hybrids PP9539 and AN447 with 1.168 and 0.684 t/ha respectively;. and the hybrids with the best heterosis were PP9539 ( 2.269 ) and A7500 ( 1.170 ). The most related hybrids were AS910 and AN450 with a genetic distance of 0,033 and heterosis of -47,68 percent whereas the most diverse were AN454 and A7500 with a genetic distance of 1.418 and heterosis of 12,26 %.

Genetic Gains of Full-Sib Families from Disconnected Diallels in Loblolly Pine

Abstract Breeding values for the 2nd-cycle of the loblolly pine (Pinus taeda L.) breeding program were analyzed with the NCSUIndustry Tree Improvement Cooperative database to estimate genetic gains and compare different strategies for full-sib deployment. In the disconnected half-diallel mating design used for loblolly pine, six parents within each diallel were crossed to generate 15 full-sib families for general combining ability (GCA) and specific combining ability (SCA) estimates. Parents among disconnected diallels were never crossed, and the SCA and full-sib family breeding values cannot be estimated directly. Using the GCA and SCA estimates from 60 diallels in the Atlantic Coastal region of loblolly pine, genetic gains were estimated in this study for full-sib families within the disconnected diallels and then compared with the potential gains that would be expected if we select parents for full-sib families based on GCA values for all parents within a geographic region. As the dominance variance was found to be much less than the additive variance, the SCA contribution to the full-sib genetic gain was relatively small. Higher full-sib genetic gains were obtained by crossing the best GCA parents from different diallels within a geographic region than selecting only those within diallels. The difference increased with increasing number of selected full-sibs. Results from different selection scenarios, with various selection intensities and relatedness managements, suggest that selection based on GCA from all parents within a geographic region would result in a higher genetic gain for full-sib families in loblolly pine. The deployment of full-sib families are very important for achieving higher genetic gains in a loblolly pine breeding program. But they were not due to the SCA contribution, but rather due to high GCA of best parents in creating these full-sib crosses. The strategies for family and clonal deployment are very attractive based on the data from this study.

General and specific combining ability from partial diallels of radiata pine: implications for utility of SCA in breeding and deployment populations.

Variances for general combining ability (GCA) and specific combining ability (SCA) and the relationship between mid-parental GCA and SCA effects were estimated for tree diameter (DBH) from a series of 20 sets of 6x6 half-diallel mating experiments in radiata pine, planted at ten sites across Australia. Significant SCA variance for DBH was almost equal to GCA variance for the combined analysis of all ten sites. The importance of SCA variance varied among sites, from non-significant to SCA variance accounting for all genetic variation among full-sib families. Significant SCA x site interaction was detected among the ten sites. A significant and positive correlation between mid-parental breeding values and best linear unbiased predictions of the SCA effects was observed. About a quarter of extra genetic gain is achievable through use of SCA variance if selection is based on the best breeding values. To fully exploit genetic gain from SCA variance in a deployment population, positive assortative matings are required for the best parents. It is estimated that the additional deployment gain of 46.0% for ten sites combined, or 52.9% for four sites combined that had significant GCA as well as SCA effects, were achievable relative to gain from GCA only, if all SCA variance within this breeding population was exploited. For a breeding population, selection for breeding values may be sufficient due to positive correlations between breeding values and SCA values. For a deployment population to capture more SCA genetic gain, it is preferable to make more pair-wise mating for parents with higher breeding values.

Genetic analysis of tolerance for phosphorous deficiency in rice (Oryza sativa L.)

The inheritance of phosphorous (P) - deficiency tolerance in rice was investigated by a sevenparent diallel. The parent materials involved were four P-efficient (IR20, IR54, IR28, and Mahsuri), one moderately P-efficient (TN1), and two P-inefficient (IR31406333-1 and IR34686-179-1-2-1), genotypes. Relative tilering ability (RTA) under P-deficient and P-supplemented soil conditions was the parameter used in determining the tolerance level of the different genotypes. Diallel graph analysis revealed that tolerant parents have an excess of recessive genes, while moderate and susceptible parents possess more dominant genes. Genetic-component analysis suggested that both additive and dominance gene effects are involved in the inheritance of P-deficiency tolerance in rice. The trait exhibited over doiminance as confirmed by the graphical analysis. Narrow-sense heritability of the trait was moderate (0.50) and environmental effects were low. Both the general combining ability (GCA) and the specific combining ability (SCA) were significant, but GCA was more prevalent than SCA. Tolerant parents exhibited a high GCA whereas susceptibles have a very poor GCA, suggesting that tolerant parents were mostly enriched in additive genes and susceptible parents in non-additive genes. Crosses involving two high general combiners showed low SCA effects whereas crosses between poor general combiners manifested highly-significant SCA values.

Genetic Improvement of Timber Yield and Wood Quality inEucalyptus Grandis(Hill) Maiden

SYNOPSIS Results of a partial diallel progeny test of Eucalyptus grandis assessed at ages 5, 36, 60 and 105 months are presented. Large genetic variations among full-sib families were found for all traits studied, e.g. the mean tree volume per family at 105 months varied from 0,226 m3 to 1,325 m3. Estimates of additive genetic variance (σ2 a) for volume production was slightly less than dominance variance (σ2 d) but for stem and crown form, and for taper σ2 a clearly exceeded σ2 d. Estimates of individual tree heritabilities were moderately high, varying from 0,28 to 0,54. Reciprocal effects were not significant. Genetic values, breeding values and specific combining ability values indicate that the relatively high level of additive genetic variation can be utilised for predicting which parent will produce the best offspring. Such offspring could be particularly useful for vegetative propagation. Genetic correlations are favourable among most growth traits, indicating that simultaneous improvements are possible even if selection is practised on one trait only. Strong age-age and trait-trait correlations imply that assessment procedures on E. grandis could be simplified substantially and that a strategy with rapid generation turnover could be adopted.

Heterosis and Combining Ability of Seed Protein, Yield and Yield Components in Long Bean1

Seven cultivars of long bean (Vigna sesquipedalis Fruw.) were crossed in diallel; the parents and F1's were evaluated in the field in 1973. Out of 42 hybrids, only three had seed protein contents significantly greater than the higher parent values. A majority of the hybrids yielded more than the higher parent. The amount of heterosis ranged from 40.7% below to 63.2% above the higher parent values. Of these, however, only two were statistically significant. Among the yield components, pods per plant showed the greatest amount of heterosis. Heterosis in seeds per pod, pod length, and seed weight were relatively low.Both general combining ability (GCA) and specific combining ability (SCA) were important for all traits measured except pod yield where only GCA was significant. Good combiners for pod yield were poor combiners for seed protein content and the SCA effects for yield depended mainly on the SCA values of the yield components.

GENERAL AND SPECIFIC COMBINING ABILITY IN SEVEN INBRED STRAWBERRY LINES

Seedlings of a diallel cross of seven strawberry inbreds omitting reciprocals were fruited in matted rows. Per acre fruit yields were comparable with leading cultivars, but berry appearance and quality of the hybrids were poor. Differences in resistance to powdery mildew reflected the values of the cultivars from which the inbreds were derived.All four characters studied showed significant general combining ability values, and three of the four showed significant specific combining ability values. These results are consistent with previous findings of considerable amounts of non-additive genetic variation in the strawberry.