Influence of flowering phenology and strobili amount on mating patterns in an Abies nordmanniana clonal seed orchard

Abstract

Clonal seed orchards (CSOs) provide improved plant material from forest tree breeding. Mating dynamics of CSOs is therefore interesting, since dysfunctions like selfing, pollen contamination and differences in clonal contributions of gametes may hamper the genetic gain. Skewed paternal contribution can be caused by clonal variation in amount of flowering/pollen production, and clonal differences in flowering phenology. Including trees from different populations in CSOs entails a particular risk that the parents are split into non-overlapping phenological classes with limited gene exchange, so the seed crop will consist of different gene pools. The study objective was to study the influence of flowering amount and flowering phenology on the mating patterns in an Abies nordmanniana CSO combining classic ocular observations of strobili with paternity analysis using DNA markers. Furthermore, we tested whether the two different gene pools from which the trees originated, had limited gene exchange. Phenology observations over three years showed that female strobili in A. nordmanniana often are receptive before the male strobili release pollen (5-7 days). However, despite clonal variation in first pollen release there is a ''great dusting day'', where all clones are contributing pollen. Based on DNA-markers, pollination success among 93 clones varied from 0 to over 5%. Clone variation in male strobili amount explained 29% of the variation in pollination success, while early pollen shedding could explain 13%. Our results support the hypothesis of early pollen shedding having an advantage in pollination success and late pollen shedding a disadvantage. No substantial mating barriers between trees from the two gene pools which are included in the CSO could be observed.