Estimation of Genetic Parameters of Haloxylon ammodendron by REML Method and Repeatability Model

This study aimed to estimate the genetic parameters of Haloxylon ammodendron located in the seed orchard of Yazd province, Iran, using REML method and repeatability model. For this purpose, among the stands of black saxaul in Yazd province, several rootstocks with suitable appearance, desirable quality, the relative balance between crown and trunk, resistance to pests and diseases selected and their seeds were sown in nursery, and the seedling were planted in the field based on a completely randomized design with unequal replications, 6 to 20 seedlings. The genotypes of each rootstock were planted on rows at 6-m intervals. Data collected and genetic parameters estimated for seedling traits as tree height, canopy expansion, trunk diameter, number of sub-branches, and freshness. Data were analyzed of variance using REML method, two different repeatability, and non-repeatability models. The results based on both models showed that the highest heritability was related to tree height. But these estimates between two methods were different so that, the genetic correlations and heritability values in the repeatability model were significantly lower than that for non-repeatability model. Repeatability was estimated based on the intragroup correlation between two independent variables on individuals and expressed as the ratio of differences between individuals to the existing phenotypic differences. Based on the results, the repeatability of the most traits was high. This result enables breeders to make good decisions about keeping rootstocks in the seed orchard during the growth stage in the early years. Finally, it was concluded that the repeatability model, could estimate moderate heritability for all of traits, which is more in line with the reality and quantitative nature of the studied traits and they could be mare affected by the environment factors.