Genetic, age, and ontogenetic variation of phyllotactic arrangements in pine species

Abstract

Variation in frequencies of phyllotactic series was analysed in three pine species: Pinus pinaster Ait., Pinus banksiana Lamb., and Pinus nigra Arn. ssp. nigricans Host. The principal unijugate, the first accessory, and the principal bijugate series were represented in 98% of the trees observed irrespective of the species. Six various accessory series were recorded in the remaining 2%. Significant species differences were found in the proportions of the three most frequent series. Within Pinus pinaster, three other sources of phyllotactic arrangements were investigated: genetic, age, and ontogenetic. No significant differences in the proportions of phyllotactic series were found between populations or between full-sib families. No relationship could be detected between phyllotactic arrangements on first season seedlings and cotyledon numbers in the seed of the same genotype. The respective proportions of the three most frequent series remained constant during the first growing season starting 3–4 weeks after germination. However there was a consistent trend of variation with age: the frequency of the principal unijugate series constantly increased from 45% at age 1 to 79% at age 11, whereas the frequencies of the principal bijugate and first accessory series simultaneously decreased. Directions of the ontogenetic spiral were evenly distributed between clockwise and anticlockwise.