[Just a final reminder to conference participants that the last day for posting messages on the theme of "how appropriate are currently available biotechnologies for the forestry sector in developing countries" is tomorrow Friday 30 June.....Moderator]

Physiological Ageing and Other Hidden Costs of Forest Biotechnology.

Dr Fenning [27 June] correctly pointed out that much progress has been made with micropropagation of elite (mature) trees. Managers need to be aware, however, that "physiological ageing" can drastically reduce gain in species where the juvenile state exhibits greater relative-growth-rate than sexually mature material. This has been demonstrated conclusively with Radiata pine and Norway spruce, and is suspected in other conifers.

Physiological ageing and its consequences, and solutions to the problem in pines have been reviewed recently (Smith, 1999). Although Radiata pine clones displayed the expected improvements in form and intra-clonal uniformity in replicated field trials, stem volumes at ages 6-10 were more than 20% lower than seedling controls. In the mid-seventies, Sweet and Wells published evidence that trees established from cuttings taken from ortets aged between 10 and 43 years showed incremental loss of ramet stem volume with advancing age of the ortets (Sweet and Wells, 1974). During the 1980's, Menzies and co-workers established extensive ortet-age-effect field trials on a number of sites. Well-replicated trials were planted using ramets from ortets ranging in age from 1 to 5 years. These trials showed conclusively that cuttings from 4 and 5 year old ortets showed average stem volume losses of 8% and 19% respectively compared to seedling controls, when measured five years after planting (Menzies et al, 1991). This effect, often referred to as "physiological ageing' has since been confirmed in a number of tree improvement trials in New Zealand (New Zealand Forest Research Ltd, unpublished data).

It is clear that any expected gain from the elite genotype is offset by volume loss due to physiological ageing. To circumvent this, many tree improvement programmes are based around techniques for maintaining the juvenile state in samples of clones, while other samples are used in clonal field trials. Cutting-edge programmes use micropropagation or somatic embryogenesis which both have very high capital and labour costs.

Many field trials with micropropagated pines species have revealed an unexpected physiological ageing in chronologically juvenile material, leading to stem volume losses compared to seedling controls. This problem can still be seen in the small number of programmes with pines where micropropagation is used in industry. Physiological ageing has not been widely reported in most conifer somatic embryogenesis work, although we did see it in early studies with Radiata pine.

The recent demonstration of rejuvenation of elite, 20-year-old Radiata pine through somatic embryogenesis induced in tissue from vegetative apical meristems (Smith, 1999) gives us some hope that the problem of physiological ageing may not concern us in the future.

While the examples above demonstrate that biotechnological approaches to tree improvement have hidden costs, so too does conventional tree breeding. Dramatic improvements in stem form and straightness have been achieved with Radiata pine in New Zealand, along with 30% gains in volume compared to the original introductions of this exotic species. Unfortunately the quality of the wood has deteriorated somewhat, with increased dimensional instability and internal checking. These problems have been overcome in part by innovations in timber drying technology, but this is itself a capital-intensive industry.

For a developing economy, it is essential to ensure that genetic "improvements" or new biotechnology does not leave a legacy of reduced stem volumes, or require extensive investment in new processing technology.

Menzies, MI, BK. Klomp, and DG. Holden. 1991. Optimal Physiological Age of Propagules for use in Clonal Forestry, New Zealand Forest Research Institute Bulletin, No. 160: p. 142.

Smith, DR. 1999: Successful rejuvenation of Radiata pine. Proceedings of 25th Southern Forest Tree Improvement Conference, New Orleans. July 1999 (in press)

Sweet, GB, and LG. Wells. 1974. Comparison of the Growth of Vegetative Propagules and Seedlings, New Zealand Journal of Forestry Science 4(2): p. 399

From Dr. Dale Smith, MetaGenetics New Zealand
([email protected])

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