The effects of scion maturation on growth and reproduction of grafted slash pine

Establishment of the University of Florida Cooperative Forest Genetics Research Program's clone banks provided an opportunity to look at scion maturation effects on growth and reproduction of many grafted slash pine clones. In 1988 and 1989, clone banks were established in nine locations in the Southeastern United States. Over 460 scion clones varying from 5 to greater than 40 years old from time of seed germination (chronological age) were grafted into the clone banks. Comparisons of diameter growth, height growth, lateral branch number and female and male strobili production were made annually for six years after grafting.Within slash pine clone banks, there were significant effects due to scion chronological age. Chronologically older scions (backward selections) grew less, had fewer branches and produced only a few more female strobili than chronologically younger material (forward selections). Forward selections produced significantly more catkin clusters than backward selections. By year six, there was no significant difference in numbers of female strobili per tree between backward and forward scions, but forward selections produced about 2.5 times as many catkin clusters as the backward selections. Similar effects on growth and reproduction due to chronological age were also found among clones within the forward selections, with older selections growing more slowly and producing fewer catkin clusters. The size and breadth of this study lends strong support to the idea that these patterns of growth will occur for grafted slash pine in any location throughout its native range.