Genetic variation of xylem formation in norway spruce ( Picea abies (L.) Karst. ) clones with contrasting growth rhytm
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- Master's theses (INA) 
Genetic variation in the progress of xylem formation and relationships with bud development in Norway spruce (Picea abies (L.) Karst.) were studied during one growing season in a clonal trial in southeastern Norway. Also the initiation of latewood formation, and the consequences for latewood percentage was studied. The study site was a clonal trial established as a classical randomized complete block design eliminating some of the site variations in growth conditions. At year 20 from stand establishment, micro-cores were extracted once a week from 16 trees representing four different clones, with known ranking of apical growth rhythm in the spring (bud flush). The sampling were continuously during the growing season from May until October 2010. Tracheid formation started in the beginning of May and ceased in August. The four clones studied were known from measurements at a very juvenile age to be contrasting in respect to timing of bud flush. One flushed very early, one very late and two were more intermediate. This were confirmed by registrations made now and also at age 20, there were significant differences between them (p<0.05). However, no significant relationships were found between the timing of bud flush and wood formation. The different phases of wood formation were measured with the result of some significant differences (p<0.05) between clones in numbers of formed tracheids in the later phases of growing season. One clone that were flushing late were found to form the highest number of tracheids but at the same time the narrowest annual ring in 2010. There were no significant differences in initiation of latewood formation, neither in latewood percentage between the clones studied (p>0.05). Thus the ones with the narrowest ring width did have greater latewood percentage. The results revealed genetic variation between the clones studied with one particular clone showing significantly higher number but narrower tracheids. Thus genetic variation in the progress of xylem formation was found, but this genetic variation seems to be fairly independent from the genetic variation in bud flush. However, this offers opportunities for further research. This study also contained a methodological study of techniques for preparation of micro-cores in the laboratory, which resulted in a recommendation of the razorblade cutting method. It was both timesaving and sufficiently accurate.