Genetic parameters for nut and kernel traits in macadamia

Abstract

Data from a trial of 40 cultivars clonally replicated over five locations were used to estimate broad-sense heritability and genetic and phenotypic correlations for important nut and kernel traits in macadamia (Macadamia integrifolia and M.tetraphylla). Location averages for each cultivar were available from 4 to 10 years after planting for nut mass, kernel mass, kernel recovery, percentage1st grade kernels and percentage whole kernels, with individual tree measurements only available for one year. Heritability estimated from location averages was inflated for all traits due to underestimation of the phenotypic variance. Un-confounded estimates of individual broad-sense heritability, obtained by combining information from both data sources, was high (H = 0.63) for nut and kernel mass, and kernel recovery, moderate for percentage whole kernels (H ≈ 0.30) and low for percentage 1stgrade kernel (H ≈ 0.20). There was little interaction between cultivar and location or age; however, for percentage 1st grade and whole kernels, there were large 3-way and 4-wayinteractions. The only strong genetic correlation was between nut and kernel mass (r g = 0.80). The implications of the results for cultivar selection and breeding programs are discussed.