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Flower induction in ash

The purpose of our task was to test systems to induce flowering in potted plants of ash trees. This was to facilitate future controlled crossing of specific lines of plants. Witholding water and application of growth retardants (paclobutrazol) were tested. A system of imposing RDI (Regulated deficit irrigation) on young seedling trees was to cause root drying and induce the production of a root-based growth regulator signals (abscisic acid) that would affect shoot growth and flower bud formation.

The treatments were applied to pot trees of seedlings in their sixth growing season; by applying water at the rates of 110%, 66% and 33% of their needs of total potential evapotranspiration (ETp). Results showed that the beneficial effects upon flowering of a single season treatment with RDI at 33% ETp and this were still apparent after two years by an increased rate of flowering. The numbers of flower buds formed per tree, however, showed no differences between treatments, whereas this had been significantly higher at 33% ETp in the year immediately after the treatment.

Flowering was also assessed in grafted plants in pots for 63 clones. Out of the 63 clones, at least one replicate for 30 clones flowered in 2004. This was considerably less than in 2003 when 42 clones flowered and generally a greater number of replicates per clone flowered. Mature seed was observed in seven clones and all produced viable seed. Flowering in both years occurred for 22 clones. There is also a suggestion of biennial flowering in some clones, were replicates that flowered in 2003 did not flower in 2004.

Application of paclobutrazol was also tested at 5 concentrations; Approximately 10 % of trees flowered, vegetative growth was reduced but there was no significant effect on the abundance of flowers or on flower numbers per plant. Overall the work showed that ash trees in pots would produce flowers, which are functional and can produce viable seeds. The methods developed will have applications in breeding work.

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Gerry DOUGLAS
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