Estimates of Quantitative Genetic Properties of Walnut and Their Implications for Cultivar Improvement1

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.

High-density Nursery System for Breeding Peach and Nectarine: A 10-year Analysis

“…When data were analyzed for correlation between stage 1 and the average of 2nd and 3rd year of fruiting in the field (stage 3) there was a slight correlation increase for CR (r = 0.62** vs. r = 0.73**), while FDP remained basically the same (r = 0.64**); however, FC decreased (r = 0.39** vs. r = 0.23), and FS, FF, and CL were again nonsignificant. The results indicate that evaluation for the statistically correlated traits can be made with reasonable accuracy in the fruiting nursery, in part because these traits have high heritability (h2) values as compared to breeding populations of other fruit crops (3,(5)(6)(7)10). Although ratings on desirable selections for FS and FF were not correlated between stages 1 and 2 and between 1 and 3, all ratings were consistently high, Table 1.…”

“…Estimates of variance components for CR, FDP, CL, FC, FF, and calculated daily gain (Table 2) obtained for a random sample of selections and cultivars on budded trees during 1982, 1983, and 1984 indicate major genetic control of most of the traits, except for CL and daily fruit gain. CR is reported to be highly affected by environmental fluctuations (6 ); however, the data covering the period from 1982 to 1984 show that the effect of years was unimportant on CR for this population sample, perhaps because CR is evaluated by comparison to bloom time in reference cultivars and a precise evaluation for CR was obtained. FDP also showed low genotype x year interaction (included low error), probably because this trait also involves CR completion as the beginning date.…”

Tracing Superior and Late-Leafing Genotypes in their Origin Center for Managing Late-Spring Frost in Walnut Orchards

“…This study showed superior genotype leafing times to be 25 to 40 d following the reference standard (Table 4). Although the phenological traits (e.g., LD) depend on environmental conditions [8], they are highly heritable [17,32]. Hence, evaluating phenological and other traits with high heritability can be vital to the success of the germplasm evaluation method for identification of superior walnut.…”

Inter- and Intraspecific Variation in California Black Walnuts

“…However, high heritabilities have been reported for phenological traits (dates of leafing, flowering, and harvest) in /. regia (7) and for leafing out in /. nigra (3).…”