The effects of self-fertilization on Green Wattle (Acacia decurrens Willd.) and Black Wattle (Acacia mearnsii De Wild.).
The genetic study of A. decurrens and A. mearnsii reported shows that self-fertilization in both these species leads to the presence of numerous deleterious recessive genes in the population and a decrease in fertility and general vigour. The bark yields at harvest of S1 and S2 families in A. decurrens and S1 families in A. mearnsii were compared with their respective progenies from open pollination. In all three trials there was a drastic drop in bark yield in inbred families, and this was somewhat out of proportion to the initial depression of height and diameter attributable to inbreeding. When S1 and S2 progenies were grown with progenies from open pollination in the same trial, the initial depression in vigour of the inbred progenies attributable to inbreeding was exaggerated by competition with the more vigorous progenies from open pollination. The consequent desirability of preventing inbreeding in seed orchards as far as possible is discussed. The possibilities of using inbreeding as a means of tree improvement, by selection in S1 or S2 lines and subsequent recombination by open pollination in a clonal seed orchard, are suggested.