Juvenile - mature (JM) correlations and selection efficiencies among one-year old Pinus pinaster seedlings and 8-yr field performance were analyzed in order to study the possibilities of early selection in the maritime pine breeding program in Galicia (NW Spain). Twenty four open-pollinated families from a first generation clonal seed orchard were grown in the greenhouse under two nutrient crossed with two water regimes. Several growth and dry mass traits were assessed 30 weeks after sowing and compared with field performance (height, diameter and volume) of four 8-yr-old progeny tests established in the coastal area of Galicia. Family mean correlations and genetic correlations were computed for each greenhouse trait, greenhouse treatment, field test site and field trait combination. Except for a few cases, most of the JM correlations were weak and in many cases negative. There was no detectable pattern of JM correlations regarding to combinations of greenhouse treatments and test site water availability and/or fertility. The large variation in the JM correlations for the same traits in different environments and sites (even changing sign in several cases) suggest a large influence of the genotype x environment interaction in the JM estimations. Other possible causes of the weak JM correlations are discussed. Based on the results of this study it may be concluded that none of the combinations of trait and treatment included in this experiment can be recommended for incorporation into early testing in the Galician Pinus pinaster breeding program. Indications for further research to optimize an early selection procedure are included.
Reproductive phenology was studied in a Pinus radiata seed orchard, located in northern Spain. Timing of flowering was determined on the basis of data recorded by visual observations made in 2000, 2001 and 2002. The genetic and environmental factors affecting female and male phenology, as well as reproductive synchronization, were studied. The dates of beginning of the receptive phase and pollen shedding varied greatly from year to year but the variation on the sum of degree-days was low. In general, the flowering periods of the different clones overlapped. The clonal differences in the phenology of receptivity and pollen shedding were in most cases statistically significant. The time needed to reach flowering stages was under strong genetic control. Genetic control was stronger for the female than the male flowering process. However, correlations between years were stronger for male than for female flowering phenology. The male flowering clones that best synchronized with the females appeared to be those that started flowering earlier. The phenological overlap index varied greatly among clones, whether male or female, and also among years.
The magnitude and practical importance of family x site interactions for growth and form traits in maritime pine (Pinus pinaster Ait.) breeding in the coastal area of Galicia (NW Spain) were analysed using several different techniques. Data were from 58 8-yr-old half-sib families planted across four sites. The analysis of variance and the ratio of interaction to family variance component showed the interactions to be quantitatively important for several traits, especially for volume and straightness. Genetic correlations between the same trait at different sites were moderate and highly variable, especially for certain pairs of sites. The results indicated that interactions are a consequence of few highly interactive families that may be particularly sensitive to environmental variation. The removal of these families from the breeding program appeared as an effective strategy to solve the interactions. Results are discussed in relation to the stability parameter considered to identify the most unstable progenies.
M. E. Miranda-Fontaíña, J. Fernández-López, A. M. Vettraino and A. Vannini
The resistance of chestnut clones to Phytophthora cinnamomi was evaluated by a soil inoculation experiment under controlled environmental conditions, as well as by excised and intact stem tests. One-year-old plants of fifty different clones were inoculated with two isolates of Phytophthora cinnamomi and evaluated fourteen weeks after inoculation. There were significant differences among clones for all root and collar rot variables. There were significant differences for isolates of P. cinnamomi but only for the collar rot variables. A total of 84% of plants grown in infested soil showed symptoms of root rot but only 50% of the plants with root rot, showed also had collar rot. The roots of resistant clones were able to confine the colonization, in roots and from roots to collar. Percentage circumference of collar rot was the best indicator or descriptor of sensitivity, a 50% of clones were resistant or highly resistant clones, with respectively less than 20% and than 10% circumference of collar rot. Percentage of survival of plants is not sufficient to indicate resistance to the pathogen, as mortality may be affected by environmental conditions or by other pathogens. The clonal heritability of collar rot variables ranged between 0.54 and 0.71. The plants grown on inoculated soil showed a reduction in growth. The phenotypic and genotypic correlations between soil infestation characteristics and the length of necrosis in both intact and excised stem tests were positive and highly significant and indicated similar resistance rankings of the clones.