Quantitative genetic analysis in Phalaris tuberosa II. Assortative mating and maternal effects in the inheritance of date of ear emergence, seed weight and seedling growth rate

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Abstract
The variation shown by the Australian Commercial population of P. tuberosa in respect of date of ear emergence, seed weight and seedling weight has been analysed, and the interrelationships among the variables characterized. All three characters show appreciable additive genetic variation, in the sense that approximately seven generations of artificial selection would be sufficient to push the population mean for each trait beyond the range shown by introduced ecotypes.Apart from the positive association between seed weight and seedling weight due to maternal influence, the three variables are to a large extent genetically independent in this locally adapted interbreeding population. It is therefore probable that the negative ecotypic correlations between seedling growth rate and date of ear emergence, and between seed weight and date of ear emergence, would rapidly be dispelled under random mating in a synthetic population.Under open-pollination, date of ear emergence has been shown to be subject to phenotypic assortative mating of degree ρ = 0·78, approximately 53% of the variation being additive genetic. Variation in seed weight within the strain is extensive, with a heritability of 0·79. Neither character shows evidence of important genotype × years interaction.Variation in seedling weight involves an appreciable genotype × environment interaction component, and has a heritability of only 0·17 which includes variation due to genetically determined maternal effects. The correlation between the seed weight of an ovule parent and the ‘ true’ mean seedling weight of the derived maternal half-sib group is of the order of 0·57. It has been estimated that the correlated response per generation in seedling weight, due to selection for seed weight, is 0·54 times that expected from direct selection.