Search Results
Abstract
The feasibility of genetically curtailing the period of sexual repression in peach and nectarine seedlings was studied by assessing the propensity of 2-year-old seedlings in a dwarf peach and nectarine breeding stock to produce flowers and fruit. Mean flower number, in a breeding stock comprising about 6300 seedlings from about 300 families, was estimated to be 9 per 2-year-old seedling; with a narrow sense heritability 0.16 ± 0.02. Mean fruit number in this population was estimated to be 3.7 per 2-year-old seedling; with a heritability of 0.33 ± 0.03. It was estimated that 3 cycles of “mass selection” on this trait could increase mean fruit number to about 13 per 2-year-old seedling, thus facilitating a reduction in the minimum length of selection cycles in this breeding stock from 3 to 2 years.
Abstract
A study was initiated in 1976 to establish the productivity of peach trees dwarfed by the recessive dw gene. This mutant gene limits plant stature (to about one-third that of standard peach cultivars) by markedly reducing shoot intemode length (2). Yield data obtained during the 2nd and 3rd year of the study indicated that trees dwarfed by the dw gene are more precocious than standard trees as they are usually grown (2, 3). These data also suggested that the productivity per unit area of mature dwarf trees should exceed that obtainable from standard trees.
Abstract
Genetic and environmental components of variance were estimated in 2 seedling populations of plum and prune at the University of California, Davis, California; the first population comprised 90 progeny of 14 open-pollinated parents, the second, 430 progeny of 50 controlled crosses among 28 parents. The estimates of phenotypic and genotypic variability associated with these traits in these 2 populations were nearly identical. Heritabilities, estimated by regressing the 500 progeny from the second population on their 50 mid-parents, were very high (0.80–1.0) for fruit size measurements and ripening dates, but zero for fruit yield. Also high (0.49) was the maximum heritability of percent soluble solids, estimated by the genetic variance/phenotypic variance. Phenotypic correlations among the traits fruit size, ripening date, and percent soluble solids are also small but significant in this seedling population. These results indicated that the rates of gain to be expected from mass selection on such populations are substantial.
Abstract
Estimates were obtained of the means, variances, and heritabilities of 10 commercially important traits from approx 200 parents and their more than 2,000 offspring observed over a period of 8 years. After adjustment of measurements for the effects of yearly variations in climate, heritabilities were found to be very high for ripe date; high for bloom date, amount of bloom, fruit length, suture, and cheek; modest for fruit firmness and acidity; and low for percent soluble solids and crop. The implications of these results on the design and execution of breeding programs in such crops are discussed.
Abstract
Heritabilities and phenotypic correlations among 18 traits of walnut (Juglans regia L.) were estimated from measurements obtained over 14 years from approx 200 families including a total of more than 2,000 offspring. Prior to this analysis the data were statistically adjusted to mitigate the seriously confounding effects of fluctuating annual climate on estimates of genotypic value. The heritabilities were then estimated by regressing the average performance of each seedling, during its 1st 2 years of production, on its mid-parent performance. Heritabilities are above 80 for leafing date, 1st shedding of pollen, receptive date of pistils, harvest date, shell thickness, all nut and kernel measurements and wt. They are above .39 for last shedding of pollen, fruitfulness of laterals, shell seal, number of light colored kernels, kernel veins, and kernel spots, and approx zero for crop and number of good kernels. The precision of these estimates is very high. Thus they should be reliable predictors of rate of genetic gain attainable in such populations when seedlings are selected as parents on the basis of their own performance. The implication of these genetic relationships on the effectiveness and efficiency of breeding methods and selection procedures in walnut are discussed.
Abstract
Means and variance components were estimated for genotype, environment (year), and genotype-year interactions for 28 nut and kernel traits of almond (Prunus amygdalus Batsch). The analysis involved over 2,500 genotypes and 20 years of observations. Estimates of heritability were obtained for 19 traits. The latter analysis involved some 100 families. The genetic component of variance and heritabilities tended to be large for shell type, size, shape, double kernels, bitterness, and crease. Year and genotype-year effects were large for quality factors such as shell and kernel color, callus, shriveling, pubescence, grade, blanks, smoothness, gumminess, and broken and split kernels.