Estimation of relationship coefficients among progeny derived from wind-pollinated orchard seeds

Abstract

Statistical analyses of trees produced from wind-pollinated seeds to determine levels of additive variance need to be adjusted to compensate for the relationships among the progeny. The assumption that the coefficient of relationship among the progeny is 0.25 will lead to inaccurate estimation of the additive variance if the relationships among the progeny are not entirely half-sib. Foreign pollen intrusion into the orchard pollen cloud, selfing, and reproductive phenology variation (i.e., mating proportion differences) among the parent trees may lead to varying proportions of self, self-half, half-sib, and full-sib relationships among the progeny. The variance of the coefficient of relationship from 0.25 for two coniferous seed orchards subjected to simulated selfing and foreign pollen problems illustrate the need for caaution when estimation techniques are employed.

Microsatellites used to establish full pedigree in a half-sib trial and correlation between number of male strobili and paternal success

“…The mating probabilities of trees in a CSO can differ, and this may warrant for a correction of the average genetic correlation, if the variance components are to be estimated from the progeny coming from the CSO seed crop (Askew and El-Kassaby, 1994). The highly skewed distribution of paternal contributions to the offspring revealed by the paternity analysis is very much in line with previous studies in Abies CSOs.…”

“…Some of the earliest studies dealing with the influence of mating patterns in forest trees in relation to the genetic relatedness among offspring were carried out by Surles et al (1990) and Askew and El-Kassaby (1994). The former investigated two leguminous tree species, and the latter dealt with two conifer CSOs.…”

“…None of the studies had the option of full paternity analysis -e.g. Askew and El-Kassaby (1994) combined a simulation approach with data on reproductive overlap. For a 15-clone CSO of Loblolly pine (Pinus taeda) without selfing and pollen contamination Askew and El-Kassaby (1994) estimated that 88.7 to 92.3% of the pair wise progeny relationships were of the half-sib type.…”

Genetic information from progeny trials: a comparison between progenies generated by open pollination and by controlled crosses

“…Doubts have been expressed as to whether the assumption of true half-sibs is reasonable for progenies generated by open pollination (Askew and El-Kassaby, 1994;Borralho, 1994;Squillace, 1974). However, there are few reports of studies using experimental data to prove or refute the validity of this assumption with respect to the estimation of genetic parameters.…”

“…One of these assumptions is that all progeny of a maternal tree are pure half-sibs, resulting in an additive coancestry coefficient of 0.125 (Falconer and Mackay, 1996). The reliability of this assumption has sometimes been challenged, since it requires that all progeny have different fathers (perfect panmixia) and that no offspring are produced by self pollination (Askew and El-Kassaby, 1994;Squillace, 1974). Violation of these requirements usually results in overestimation of both additive genetic variances and prediction of genetic selection gain.…”