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.
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Hansche et al. (1972) studied this question.