IUFRO Breeding theory and progeny testing

Virtually all plantation forestry in New Zealand is based on exotics, and 95% of current planting is of Pinus radiata, for which an intensive breeding programme has been progressing since 1950. There has been ongoing importation of seed and domestication of exotic tree species since the second half of the 19th century, with adequate documentation of seed sources from about 1920 onwards. Formal tree improvement research started in 1950 with the appointment of I.J. Thulin from Denmark, a student of pioneer forest geneticist, Syrach Larsen. He initiated a programme of intensive establishment of provenance trials of a wide variety of conifers lasting from 1955 to about 1970, paralleled by the initial development of radiata pine breeding and seed orchards. Provenance trials were planted, often at many sites, of Pseudotsuga menziesii, Pinus ponderosa, P. contorta, P. attenuata, P. monticola, Picea sitchensis, Tsuga heterophylla, Thuja plicata, and various Abies species from the Pacific Northwest USA, P. strobus, P. elliotii, P taeda, P. virginiana, from the eastern USA and Pinus nigra, P. pinaster, Larix decidu from Europe, Larix leptolepis from Japan, etc. Later attention was given to a large number of Mexican pines, such as P. patula, P. pseudostrobus and P. michoacana, and later still to P. muricata, a close relative of P. radiata. The breeding programme for radiata pine had proceeded within the NZ land race, composed of two of the three Californian populations, and provenance testing had been delayed, beginning in 1963, and was repeated more intensively with establishment of extensive gene resources in 1980.

Douglas-fir breeding

Douglas-fir improvement started with provenance trials of large numbers of provenances in 1957 and ’59. The first series was from mainly commercial seedlots from a wide range of environments in Washington and Oregon. The 1959 series was mainly from specially-collected seedlots that sampled the coastal fogbelt populations from Santa Cruz in California to Puget Sound in Washington, and was planted on 16 sites. There were only one to three plots of each provenance per site but the allocation of provenances to sites was largely balanced and 144-tree plots were used, thinned over the years, leaving about 25 trees today when the trials are still giving valuable data on yield per ha at harvest age. Unfortunately the early results of the provenance trials were not taken into consideration when planning the first plus tree selection and progeny testing programme in 1969. In retrospect, the five-year results showed clearly the superior growth of Californian and southern Oregon coastal provenances and thus we should have been selecting in these southern coastal fogbelt populations. However the only representatives of those populations were in the provenance trials and they were only aged 10 years from planting in 1969. The decision was made, wrongly as it turned out, to select a breeding population in the ca. 40-year-old stands of Washington origin, planted in Kaingaroa Forest in the North Island in the Depression. 185 parents were selected and grafted and OP progeny tests established with little delay in 1971 and 1972. The programme was put on hold by 1974, partly for these reasons and partly because the industry lost interest in Douglas-fir at the time because it could apparently harvest two crops of radiata pine to one of Douglas-fir.

Later in 1988, in the wake of high log prices, industry interest revived and a new breeding programme was started with 180 selections made largely in the better coastal fogbelt provenances in the 1959 provenance trials. Plus trees were grafted in an archive and it was planned to use polycrossing of these clones for GCA testing and pair crossing to form the breeding population. This strategy failed to deliver sufficient seed and crosses and has recently been revised to rely on OP seed from the clonal archive for generation turnover and breeding value estimation. At the later selection of the next generation of parents, parentage analysis by DNA markers, it is hoped, will avoid selection of full siblings from different OP families

A second “superline� of 220 selections was made in 1993 in California and Oregon native stands and an OP progeny-provenance breeding population planted in 1996. This project was supported by the newly-formed FRI-Industry Douglas-fir Cooperative which continues to support research in various areas including tree breeding. These two superlines of unrelated parents could form the basis for control-pollinated orchards with vegetative multiplication in the future, as used widely in radiata pine, Recently the economic importance of timber stiffness has been recognised and stiffness as well as yield and log quality established as breeding objective traits. Wood density or stiffness was not a selection criterion in the selection of parents of both superlines, and to remedy this, a “Stiffness Elite� population is being established through phenotypic selection in second-generation land-race stands of Fort Bragg, Californian origin for sound velocity (measured non-destructively by the IML hammer) as well as diameter and stem straightness. Seedlots from this land race have proved top performers for volume growth in the 1959- and 1996-planted trials. The Elite breeding population, initially of 100 OP families, will eventually be culled to about 25 forwards selections from the best families and will form a pre-production population, turned over in future by at least twice as many full-sib families as parents. Rapid reduction in status number will be alleviated by infusion of the best parents from the two Main population superlines.

Eucalypt breeding

From 1975 to 1980, species trials of a variety of eucalypt species, mostly species suited to pulping, and provenance-progeny trials of Eucalyptus regnans, E. fastigata, E. nitens, E. delegatensis and E. saligna were planted. These provenance-progeny trials formed modest-sized breeding populations of 80 to 150 families, mainly of native Australian seedlots but also included open-pollinated (OP) progeny of NZ-selected plus trees. From 1988 onwards, second generation breeding populations were established under a new Forest Research Institute-Industry Breeding Cooperative that was solely interested in growing eucalypts for short-fibred pulp. No further work was done on E. saligna and E. delegatensis and second-generation open-pollinated breeding populations were established of E. regnans, E. nitens and E. fastigata, based on forwards selections from the earlier provenance-progeny trials and from Australian progeny tests, including additional native population progenies. There were 300 OP families in E. nitens and E. regnans populations and 150 for E. fastigata. The E. regnans programme was subsequently put on hold, as the industry ceased planting this species for pulp because of disease problems.

In the second generation breeding populations of eucalypts, a strategy was developed around using open pollination of forwards selections as the means of cycling the breeding population, in conjunction with sufficient sublines to allow one clone per subline to be incorporated into future clonal seed orchards. The 300 families of E. nitens were planted at two sites in single-tree plots in a sets-in-reps design to estimate breeding values, and planted at another site by subline blocks of 30 families each, as isolated “forwards-selection blocks� (isolation of these was achieved by planting these blocks in a matrix of another species, with separation between blocks of 50m, sufficient isolation for insect-pollinated species). The intention was for the single-tree-plot trials to provide breeding values of families, and the forwards selection blocks to be used for providing OP seed of forwards selections for the next generation of the breeding population. Unfortunately, in the case of E. nitens, neither single-tree-plot trials nor the forwards selection trial produced any seed. We learned that E. nitens has to be planted at higher altitude and colder sites to flower. The strategy had then to be modified by grafting forwards selections and planting them in clonal archives on good-flowering sites. Here open-pollinated seed is being collected for establishing the third generation breeding population, without regard to the original sublining. Pedigree reconstruction by DNA markers has been employed successfully to identify the male parents of seeds from open pollination in the archive, which will help avoid problems of future related matings and inbreeding.

Improved seed production by clonal seed orchards has been developed for E. nitens and E. fastigata, based on forwards selection of the best individuals from the best families, first in the 1975-80 provenance-progeny trials and later from the second generation progeny trials. OP seedling seed orchards were primarily employed in the first-generation E. regnans programme.

There is interest among NZ’s small growers in growing eucalypts for sawn timber, and recent research has concentrated on species introduction and testing of a group of naturally-durable stringybarks and a few other species with good reputations for less growth stresses, good sawn timber characteristics and lack of disease and insect problems. These include E. pilularis and E. muelleriana, species well-known in NZ for good sawing and sawn timber characteristics of appearance-grade lumber, including natural durability. Recent deterministic gain simulation studies have shown that it is possible to get good genetic gains from miniaturised breeding programmes on a one-shot single generation basis, and this approach is well suited to progressing the genetic improvement of promising species of which there are some genetic resources (e.g. provenance trials) but where there is no immediate demand for seed.

Cypress breeding

Breeding programmes for the two cypresses, Cupressus macrocarpa and C. lusitanica have been created from open-pollinated families from selected plus trees from NZ stands, from native populations at Monterey, California (for C. macrocarpa) and from overseas breeding programmes (for C. lusitanica) and were planted in 1983-4. Breeding populations have been cycled at ages 12-13 by collecting OP seed from forwards selections from these family test/breeding populations and planting new family trials. The C. macrocarpa first generation population consisted of 75 NZ-selected families and 75 from the native populations. The C. lusitanica first generation population was of 111 families, 83 from NZ and 28 from Kenya and Columbia. Forwards selection have been made in both species’ OP progeny trials and propagated in clonal seed orchards. Also, OP seedlots from the best selections have been cloned by 10 clones per family and clonal tests established for selecting clones for deployment by clonal forestry. Ageing of clones is being delayed by hedging stool beds, though this is unlikely to be a long-term solution. Research on flowering is helping to develop control pollination techniques, surprisingly difficult for cypresses, and interspecific hybrids are intended among Cupressus species and with Chamaecyparis nootkatensis. The well-known Leyland and Ovensii hybrids of C. macrocarpa and C. lusitanica with Ch. nootkatensis perform well in NZ and it is intended to create more of these hybrids.

General

The recent re-adoption of open-pollination as a means of turning over generations in breeding populations, especially the large Main population in the radiata pine programme, depends on development of pedigree reconstruction by DNA markers for avoiding excessive relatedness, inbreeding and reduction in status number. There are early indications that this can be done in pines and eucalypts and that it will be much less expensive in future. Provided that an open-pollinated breeding population is thinned selectively before seed collection from forwards-selected parents, and the population is being managed by balanced within-family selection for sustaining status number over generations, gains are predicted to be satisfactory and better than from full-sib families. Costs can also be reduced and breeding cycles shortened, making breeding more efficient. Combining such an OP Main population with a small, cloned, full-sib-mated elite can provide a good strategic solution. Cloning breeding populations has not been widely practised but has the capability of increasing gains from forwards selection for traits with heritability less than 0.5. Cloning breeding populations families can also allow rapid generation turnover with CP crossing, if all clones are also managed for seed production in a clonal archive. These ideas are likely to be adopted where appropriate in “alternative� species breeding in the future.

Breeding strategies for the “alternative “ species have evolved very much in parallel with experiences in the bigger radiata pine breeding programme, and have always had to be based on economical solutions. Many expensive mistakes have been made yet the future prospects for realising high gains are good, and the breeding populations and breeding strategies adopted are robust and should withstand changes in selection criteria and new pests and diseases.

Authors: Tony Shelbourne¹, Charlie Low¹, Ruth McConnochie¹ and M.D. Wilcox².

¹Ensis-Genetics, Private Bag 3020, Rotorua, New Zealand.
²JP Management Consulting, PO Box 73-141, Auckland, New Zealand.