Genetic Survey of Pinus Radiata. 4: Variance Structures and Heritabilities in Juvenile Clones

A clonal adjunct to a large Pinus radiata D.Don provenance-progeny trial involved six populations (all the natural populations except Cedros, plus two "land-race" populations from New Zealand) x 30 wind-pollinated progenies (families) x two clones nested within each of two sites x four ramets per clone. The clones were cuttings taken from previously hedged 3-year-old ortets at c. 55 cm height, and came from a subsample of the seedling families used in the main experiment. Genetic parameter estimates from the clones were compared among populations and with estimates from the seedlings. The parameters estimated included broad-sense heritabilities (H) v. narrow-sense heritabilities (h), phenotypic variances (addressed largely as coefficients of variation), alternative estimates of genetic variances (total genetic v. additive genetic), and genetic variances between and within families in clonal material. Genetic correlations between performance in seedlings and cuttings of the same families were also studied. Phenotypic variances appeared-similar between the cuttings and parallel genetic samples of seedlings. Genetic correlations between seedling and clonal performances appeared to be generally high (>0.75). These results accord with genotypic effects being very similar between the propagule classes, with important implications for selection and predicting genetic gains. Estimates of H were very similar, trait for trait, among populations. This, despite some smaller coefficients of variation in New Zealand material, suggested that genetic variance structures are similar between populations. Estimates of h, made under the provisional assumption of random (i.e., 100% half-sib) mating, tended to be lower in New Zealand than in native-population material, particularly for cumulative growth traits and some tree-form traits including butt straightness, stem straightness, and branch habit quality, so that h tended to vary^much more between traits than H. Such h values, however, tended to resemble H more in the native populations than in the New Zealand. This, and markedly higher ratios of between-family: total clonal variance ( a 2 : a 2 [ a 2 = a 2 + a(f)]) in cuttings of native populations, strongly indicate much greater departures from random mating in natural stands than in plantations. Although differences between h (assuming random mating) and H in New Zealand material tended to be greater in the traits previously reported as showing * Present address: Acacia Road, Lake Okareka, R.D.5, Rotorua, New Zealand New Zealand Journal of Forestry Science 22(2/3): 187-210 (1992) 188 New Zealand Journal of Forestry Science 22(2/3) relatively high levels of specific combining ability, they suggested a generally higher proportion of non-additive gene effects than did earlier reports. Also, the ratios of Gf / G in cuttings were hard to reconcile with likely mating patterns in natural stands, unless non-additive gene effects were less than suggested by comparing h and H.