Genetic variation in seasonal growth patterns in radiata pine in Galicia (northern Spain)

Shoot elongation patterns in 2 and 3-year-old Pinus radiata seedlings were monitored twice a month during 2003 and once a month during 2004 in three progeny tests in northern Spain. Fifty-eight half-sib families were studied. Several annual growth parameters were measured in each seedling: initiation, termination and duration of height growth and number of new buds formed each year. Total height, internode length and frost resistance were also measured in each seedling. The variation in these traits among families and sites was studied, as well as the effects of environmental parameters (temperature and rainfall) on growth phenology patterns. The extent to which bud phenology is genetically controlled and related to growth traits was examined. Families differed significantly in total summer shoot growth and number of summer flushes (lammas growth). The number of cycles produced per year ranged from one to four. Monocyclic families grew throughout the year, whereas polycyclic families grew episodically, depending on rainfall.Heritabilities within sites were moderate and very similar between years and sites for the dates of bud burst and the number of new buds formed. Bud burst was positively genetically correlated with seedling height. Thus, selection for greater growth is expected to delay bud burst. The number of new buds formed each year was negatively correlated with height and internode length, which means that monocyclic families were taller with longer internodes than polycyclic families. Thus, selection for faster stem growth in young progeny tests is expected to increase the length of internodes in the next generation, to reduce the number of flushes per year and to delay the bud burst date, thereby avoiding late spring frost damage.