The development of Dothistroma-resistant radiata pine for planting in Victoria.  L. A. Pederick, I. R. Bail and C. R. Dean.  April 1993.  35pp. (unpubl.)

SUMMARY

Variation in crown infection of radiata pine by pine needle blight (Dothistroma septospora) was assessed in two series of progeny trials near Myrtleford. The data were analysed to determine genetic parameters controlling the infection in these trials and to estimate the breeding value of many individual clones used as parents and families in the trials.

The first series of progeny trials, planted in 1985 on an ex-pasture site near Lake Buffalo, contained, among other material, 45 families arranged in three half-dialled groups, each with 15 families comprising all the crosses possible among six parent clones. The half¬diallel groups of families were very suitable for the analysis of genetic influences on infection. The trials were assessed twice, in October 1988 when crown infection was light (about 10%) and in October 1989 when it was very heavy (about 60%).

Heritability of infection was estimated as 0.28 in 1988 and 0.21 in 1989. These estimates are high enough to indicate that good progress could be made by breeding for resistance, with gains of up to 15% reduction in crown infection possible from one generation of breeding. The similarity of ranking of families obtained in the two years and the higher estimate of heritability in the first year indicates that conditions of light infection are quite satisfactory for ranking families for resistance and appear better for this purpose than heavy infection.

The ratio of additive to dominance genetic variance was 1.8 and 3.4 in the two years respectively. On account of the large additively inherited component of resistance, predictions of the resistance of families produced by controlled pollination, based on knowledge of the general combining ability of the parent clones, should be fairly accurate.

The magnitude of the estimates for heritability and the ratio of additive to dominance variance conformed well with estimates published by workers in New Zealand.

Stem deformity was more strongly inherited (h²=0.47 and 0.60) than Dothistroma resistance and there also was a high ratio of additive to dominance genetic variance (1.9 and 6.7). However, the genetic correlations between Dothistroma resistance and stem form were negative, though low, indicating that it would be difficult to breed for both resistance and non-deforming stems on fertile pasture sites.

In other parts of the 1985 trials, plants of Guadalupe Island provenance were more susceptible to the disease than those of Victorian seed orchard origin. The variation among families was large.

The second series of progeny trials, planted in 1986 on an ex-pasture site at Blades Block, Dandongadale, contained a very large number of families also grouped in half-diallels. However, on account of missing families in each half-diallel or fewer progeny or replications, they were less suited to genetic analysis than the Lake Buffalo half-diallels, but were quite suitable for estimates of family and parental clone effects.

With the data from the two series of trials, the breeding value for resistance of 92 clones was estimated from the means of their families. Six of these clones have been identified as having very high general combining ability for resistance, suitable for immediate use for breeding of resistant planting stock.

Three procedures for production of improved plants are described and progress towards implementing these procedures is recorded.

Mass production of cuttings with moderate resistance has already commenced using cuttings from stools grown from half-sib seed of three of the six resistant clones mentioned above, plus seeds of other families of moderate resistance. Controlled pollination between resistant clones has been undertaken but the seeds are still developing. Some second generation clone selections have been made in the trials reported above, and grafted ramets have been planted in a clone bank but are not yet ready for breeding. Overall, therefore, sound progress has been made in breeding for Dothistroma resistance.