Greater Genetic Gain Research Articles

Genetic Gain and Diversity of Orchard Crops Under Alternative Management Options in a Clonal Seed Orchard of Pinus thunbergii

Abstract Genetic gain and diversity, expressed by status number, of seed crops from a clonal seed orchard of Pinus thunbergii were estimated considering selection, fertility variation and pollen contamination, and compared for different management alternatives (selective harvest, genetic thinning and combination of both options). Management variables included the proportion of clones left after selective harvest and/or genetic thinning. The impact on genetic gain and diversity of seed crops was quantified as a function of the quantity and quality of gene flow from outside the seed orchard. Genetic gain varied with the proportion of selected or thinned clones. Genetic thinning by means of truncation selection of clones resulted in a large decrease in status number, which was accompanied by greater genetic gain than achieved by selective harvest alone. As expected, gene flow from outside the seed orchard greatly increased status number of the seed crop at higher rates of pollen contamination under all management options. The formulae and results of the present study could be used for identifying favorable selection intensity and alternatives for orchard management.

Best linear unbiased prediction of clonal breeding values and genetic values from full-sib mating designs

Full-sib progeny tests with clonal replicates may provide better breeding value estimates and the greatest genetic gain in a tree improvement program. Clonal breeding values (CBV) that combine the family and within-family breeding values due to additive genetic effects can maximize the genetic gain for advanced generation breeding. Clonal genetic values (CGV) that further incorporate full-sib family specific combining ability due to nonadditive genetic effect can maximize gain for a deployment program with clonal propagation techniques. The best linear unbiased prediction (BLUP) is the best statistical method for estimating both CBV and CGV because of its desirable statistical properties compared with the heritability-based gain calculation. A BLUP method for determining both the CBV and CGV for full-sib clonal progeny tests was proposed in this paper. The formulas for CBV and CGV were derived using general BLUP methodology, and formulas were derived for the calculations of their standard errors. An analytical method by using a standard statistical package (SAS PROC MIXED) was presented for CBV and CGV calculations from any full-sib mating designs.

Estimativas de parâmetros genéticos e métodos de seleção para o melhoramento genético de Pinus oocarpa Schiede

Este trabalho teve por objetivo estudar a variabilidade genética entre e dentro de procedências e progênies e determinar o ganho genético em volume de madeira, em Pinus oocarpa Schiede. O experimento foi instalado em Angatuba, SP, em delineamento de blocos de famílias compactas, com nove repetições e parcelas lineares de seis plantas. A produtividade volumétrica média obtida de sete procedências foi de 0,296 m³ de madeira por árvore aos nove anos de idade. Para estabelecer um pomar de sementes por mudas, a seleção (no bloco) de 189 árvores (27 por procedência) com os maiores diâmetros na altura do peito (DAP) permite aumentos na produtividade volumétrica de 0,327 m³, 0,338 m³ e 0,341 m³ por árvore, na seleção individual, combinada e índice multiefeito, respectivamente. Em pomar de sementes clonais, a seleção (no experimento) de 28 árvores (4 por procedência) com maiores DAPs permite aumentos na produtividade volumétrica de 0,345 m³, 0,355 m³ e 0,356 m³,por árvore, na seleção individual, combinada e índice multiefeito, respectivamente.

Geographic Variation of China Fir (Cunninghamia lanceolata (Lamb.) Hook) in Taiwan: Analysis of Provenance Division by Ecotype and by Province

China fir shows significant geographic variation because it grows in a great diversity of ecological environments; it is subject to geographic and reproduction isolation; and it has been cultivated selectively and separately by many local farmers. In order to match provenances and planting sites for greater genetic gain, seed collection zones are to be delineated. Forest geneticists in mainland China have separated China-fir provenances into 9 ecotypes. Using growth and isozyme data obtained from 2 test plantations (Liukuei and Lienhuachih) we tested the effectiveness of such ecotype delineation. We found that the grouping of China-fir provenances into 9 ecotypes was most effective for the analysis of early growth at the Liukuei plantation. It was only moderately effective for analysis of later growth at the Lienhuachih plantation. The grouping of provenances was not useful for isozyme frequency or heterozygosity analysis. The different degrees of effectiveness may be possible because the construction of such ecotype classifications in China were based solely on early growth data; no isozyme data were used. Grouping provenances by ecotypes was superior to grouping by political provincial origins for early growth. On the other hand, provincial grouping seemed to be better than ecotype grouping for later growth. When the 2 best ecotypes or 2 best provinces were selected, provincial selection seemed to be able to yield a higher genetic gain than ecotype selection. However, the selection results and their rankings seemed to be more consistent in the ecotype division than in the provincial division.

Genetic gain with desired status number in breeding programs: a study on selection effects

Genetic gain and average coancestry or status number was investigated for five selection methods: penalty index selection (PIS), family index selection (FIS), combined between-family and within-family selection (CBW), restricted individual selection (RIS), and combined index selection (RCS). PIS was a function of an individual's breeding value and family contributions, modelled as a stepwise procedure to select superior individuals one by one. A penalty would indicate the need to have low average coancestry or large status number. Breeding populations of unrelated families were investigated by Monte Carlo simulation to examine the genetic response of the five selection methods at a restricted selection intensity and average coancestry. PIS attained the greatest genetic gain, except at the selection limits of maximum genetic gain and minimum average coancestry where PIS might be identical to the other selection methods. FIS and RCS well approximated PIS at high average coancestry. RIS was similar to RCS when the heritability was high, particularly at low average coancestry. CBW attained the least genetic gain among the selection methods. For all selections, high heritability would contribute to a greater genetic gain and status number or low average coancestry. PIS was applied to a practical breeding program in Alberta that included several subpopulations. The results suggested that the selection efficiency for balancing genetic gain and average coancestry would increase when deploying a subpopulation strategy for breeding population management.

Geographic variation pattern ofLarix olgensis

On the basis of the data of provenance test for 10 years in the total natural range ofLarix olgensis from 10 seeds collection sites, the geographic variation patterns have been made by means of canonical correlation analysis: (1) The basic variation patterns of growth characters is in vertical gradual change along the elevation gradient as principal, and gradual change along the latitude as supplement. (2) The Xiaobehu provenance with low elevation and low equivalent latitude is the good gene resource center ofL. olgensis. It has the genetic characters of rapid growth, high stability and fine timber quality. (3) The synthetical interaction between water and heat factors is the major factor to produce the variation ofL. olgensis and the temperature is the principal one. (4) Among the genetic variations of geographic population characters, the variation of growth is the most obvious one, and it could be taken as the main character for provenance division. (5) By allocating the seeds from the low equivalent latitude region to the northern suitable afforestation areas, the greater genetic gain could be obtained.

Evolutionary trends in morphological, physiological, agronomical and qualitative traits of Triticum aestivum L. cultivars bred in Italy since 1900

The agronomical, physiological and qualitative characteristics of 34 representative cultivars of bread wheat belonging to 7 generations (groups) of cultivars produced by Italian breeders over 90 years have been evaluated.Cultivars were grown for three years in replicated trials with two husbandry conditions : old, simulating that in use in the first part of the century, and modern.It was found that there was a reduction of plant height, an increase in harvest index, reduction of the vegetative growth phase associated with a progressive increase of yield potential. With the old husbandry the cultivars did not show a clear positive trend in yield potential, indicating that genetic improvement was largely dependent on or associated with a parallel improvement of growing conditions.The greatest genetic gain was achieved with the last generation of cultivars which, with modern husbandry, produced 830 kg ha−1 more than those of the previous group. This is an indication that breeding is not approaching a yield plateau and emphasizes its major role in accelerating the increase in yield potential. Moreover, modern cultivars have better quality indices than those of the previous groups, suggesting that Italian breeders were able to manipulate the genes controlling protein composition while selecting genotypes characterized by a shorter straw and an higher yield potential.It is concluded that in the present economic and political context where farmers are forced to optimize and probably to reduce inputs, old cultivars may be used in breeding programmes for low input conditions as donors of specific, useful morphological and physiological traits to be incorporated in future cultivars.

A diallel cross in black spruce

A complete 7 × 7 diallel of black spruce (Picea mariana (Mill.) B.S.P.), without selfs, planted in three locations, was measured for height growth at several ages. Analysis using Griffing's method 3, model II, demonstrated that general combining ability (GCA) was the dominant genetic component of variation, although specific combining ability (SCA) appeared to be proportionately increasing in importance with age. When data from all locations were combined, the GCA × environment interaction proved to be highly significant. If the trend of increasing proportional importance of SCA continues, existing improvement strategies exploiting only GCA may need to be radically altered. Greater genetic gain would result from crosses among a few clones of high specific combining ability. Whatever approach is used, it appears likely that genotypes will have to be carefully matched to sites. Imbalance in the data set appeared to invalidate F-tests. As a result of heterozygosity in the parents and the likely presence of epistasis and linkage disequilibrium, the interpretation of GCA and SCA variance components in terms of additive and dominance genetic variance cannot be made. Key words: diallel cross, combining ability, black spruce, forest genetics.

CLONES IN FORESTRY AND IN NATURE

Summary Clonal propagation or apomixis is common in the plant kingdom. Among trees, agamospermy and vegetative propagation are relatively rare in nature. In this paper the roles of different modes of propagation in the survival strategy of three different plant groups are discussed. Conclusions for tree breeding strategies are drawn: clones have an important role to play. Greatest genetic gain and flexibility are attained when both sexual and clonal propagation occur. Genetic diversity should be maintained in any strategy.