Karl-Anders Högberg

Critical Factors Affecting Ex Vitro Performance of Somatic Embryo Plants of Picea abies

The potential to use somatic embryos for large-scale propagation of elite genotypes, for integration into breeding programmes and for connecting breeding and mass propagation, is receiving much attention. However, before the methods are applied it is important that the plants regenerated via somatic embryogenesis grow as expected, i.e. as seedlings or cuttings. Growth of somatic embryo plants is under a cumulative influence of a number of treatments given during the in vitro phase and during the ex vitro establishment phase. The aim of this study was to identify treatments with a negative influence on the subsequent growth of somatic embryo plants of Norway spruce (Picea abies L. Karst.). Based on the results, the time of contact with abscisic acid during somatic embryo maturation and the length of continuous light treatment (CLT) during the first growth period strongly affect the height growth during two successive growth periods. In both cases longer treatments exerted negative effects. Based on these results a new method was set up, which includes: (1) prematuration treatment of the suspension culture in a growth regulator-free medium, by which the maturation step is synchronized and contracted; and (2) a two-phase germination treatment, first on a solidified medium and then in a liquid medium. This treatment avoids extended CLT during the first growth period. Another advantage of the two-phase germination treatment is a better root-system development. Somatic embryo plants produced according to this method can be transferred directly from in vitro conditions to the greenhouse.

Nursery selection of Picea abies clones and effects in field trials

The effects of early selection of clones in the nursery on field performance after 6 yrs in the field were studied in a material comprising 794 cutting propagated clones of Picea abies (L.) Karst. A 20% selection for height in the nursery gave gains of approximately 3% in height after 6 yrs. Attempts to improve the early selection procedure were made. Stratification of the nursery beds in two blocks according to location had almost no effect on the gain, arid selection within growth rhythm classes was less effective. Correlations between other characters measured in the nursery and field characters were generally low. The positive, though moderate, relationships between nursery height and height after 6 yrs in the field are encouraging for further research to improve selection efficiency.

Rooting response of late summer cuttings taken from Pinus sylvestris half-sib families

Abstract One-year-old Pinus sylvestris donor plants were top-pruned in early May, allowing cuttings of three types to develop: shoots from adventitious buds near the top of the plant (T), weaker shoots from adventitious buds emerging further down the stem (M) and shoots from normal buds on branches (B). Cuttings from 46 half-sib families were collected at the beginning of August, treated with indole-butyric acid, immediately inserted in containers with porous substrate and put in a greenhouse, where soil was heated and high air humidity was maintained. The rooting frequency, estimated by counting living plants 10 months after insertion, was 54%. The family variance component for rooting was small and non-significant, while the clone-within-family component was strongly significant and accounted for 21% of the total random variance. Type M and type B cuttings showed significantly better rooting ability than type T cuttings. Including only plants with at least four acceptable shoots in the propagation experiment, 61% of the potential donor plants remained, without loss of any family. If a more restricted selection criterion was applied, including only plants with at least eight acceptable shoots, 21% remained, with a loss of 13 families. It was concluded that rooting ability of P. sylvestris can be brought to a level that could justify its inclusion in a breeding programme. The lack of family variation was also favourable in this respect, as no families were lost owing to low rooting response. However, the number of suitable cuttings produced by the donor plants needs to be increased.

Effects of root pruning and stem injections with Gibberellin a 4/7 on flowering and cone harvest in three Picea abies seed orchards

The effects of root pruning and stem injections of gibberellin A 4/7 (GA) on flowering and cone harvest were studied in three mature Picea abies (L.) Karst. seed orchards. The trials were split into two consecutive years, two in the summer of 1988, the third in summer 1989. Both years could be regarded as good years for natural induction of flowering. No effects were found on male flowering, whereas female flowering was enhanced by root pruning in two trials and by GA injections in one. No interaction effects on either male or female flowering were detected. In two trials, an approximately three‐fold increase in number of cones per tree was obtained after root pruning and GA injections, which is a commercially acceptable increase.

Genotype by environment interaction in the southern Swedish breeding population of Picea abies using new climatic indices

Genotype–environment interaction (G × E) has a critical impact on the design of a breeding programme and the resulting genetic gains. The aim of this study was to assess the incidence and predictability of G × E with respect to growth traits in the breeding population of Picea abies (L.) Karst. in southern Sweden. We used across-site genetic correlations as a measure of G × E and multiple linear regression to detect patterns in the correlations. As independent variables in the regression analysis, we used site and geographic factors as well as a comprehensive set of new climatic variables. A main result was that G × E was low to moderate with respect to the growth traits considered and largely unpredictable based on any of the geographic or climatic variables analyzed. However, it seems that the effects of late spring frost damage are important as they created significant differences in across-site correlations and we suggest that models describing frost risks should be developed. One major implication from this study is that the same genetic material could be used over larger areas in southern Sweden than recommended today with only a marginal or no loss in genetic gain.

Relationships between early assessments of stem and branch properties and sawn timber traits in a Pinus sylvestris progeny trial

Abstract A sample of 162 trees was harvested from a 36-year-old Scots pine (Pinus sylvestris L.) progeny trial to evaluate correlations between early measurements of branch diameter, and other stem and branch traits, with sawn timber traits, and hence their potential utility for predicting wood quality. The sample trees were assigned to three genetic groups of small, medium and large branch diameter, based on parental breeding values. Bottom logs were cut and sawn, and several important traits for the visual quality of the boards were assessed. Phenotypic correlations were then estimated between these traits and measurements of the height, diameter, branch diameter, branch angle, stem crookedness, number of branches and grain angle under bark of the corresponding trees when they were 16 and 36 years old. The diameter of the coarsest knot in the board was correlated with the branch diameter at the age of 16 years (0.50), and there were significant differences in this trait among the genetic branch diameter groups. In addition, the board twist was correlated with the grain angle under bark at the age of 36 years (0.54). Thus, the field assessments of branch diameter and grain angle under bark show relevance for the visual quality of centrally sawn small timber.

Development and growth of plantlets of Pinus contorta regenerated from adventitious buds

Before micropropagation techniques can be applied to a particular species, it is crucial to optimize the method and to determine how the micropropagated plants grow in the field. Adventitious shoots developed on embryos of Pinus contorta Dougl. ex Loud, after a 2 h pulse treatment with 250 μM N6‐benzyladenine. The time to first subculture after the pulse treatment influenced the yield of adventitious shoots. On average, 68% of the adventitious shoots had developed roots 12 weeks after treatment with 1.25 mM indole‐3‐butyric acid for 6 h. The auxin treatment stimulated early rooting (i.e. within 6 weeks) but had no effect on late rooting (i.e. after 6 weeks). The size of the plantlets was of importance for their survival when potted. All plantlets with a distinct stem elongated during the first growth period while some without did not. The relative height growth rate of plantlets was similar to that of seedlings. In the field the increase of height was similar for plantlets and seedlings. Plagiotropy was h...

Field performance of Pinus contorta trees propagated vegetatively via adventitious buds

Abstract Pinus contorta plants regenerated from adventitious buds induced on zygotic embryos were planted in a field trial where growth, straightness and flowering were followed over 7 years. Seedlings were taller than the plants derived from adventitious buds at the start of the field trial. Adventitious plants did not catch up with seedlings in height after 7 years in the field, but the relative height growth was equal. The higher frequency of plagiotropic growth that was displayed by adventitious plants the first year in the field was not reflected by differences in the frequency of basal sweeps 6 years later. However, the frequency of crooked stems was comparatively high but similar among the plant types. Flowering was more abundant for the seedlings than for adventitious plants. Taken together, the results show that P. contorta can be cloned via adventitious buds from zygotic embryos, and that the resulting plants show satisfactory growth for inclusion in breeding.