Graft survival and promotion of female and male strobili by topgrafting in a third-cycle slash pine (Pinus elliottii var. elliottii) breeding program

Abstract

A total of 2561 slash pine ( Pinus elliottii Engelm. var. elliottii) grafts were topgrafted in the winter of 2003 and evaluated in January of 2004. The objectives of this study were to understand the effect of the genetic material and crown position on survival and flowering response of topgrafts. Also, the effects of geographic direction, branch order, and scion age on topgraft response were assessed. Topgrafting was an effective tool for promoting both female and male strobili. The genetic material (scion and interstock clones) and the crown position had large effects on the promotion of female flowering and topgraft survival. More than 23% of the total variation in female flowering and 16.3% of the total variation in topgraft survival were due to differences among scion clones and among interstock clones, respectively. The highest survival rate was reached by grafting in the mid-top followed by the top crown position. Grafting in the top of the crown was highly superior in promoting female strobili followed by the mid-top position. First-order branches showed a significantly superior production of female strobili. Chronologically older scions, from selections made in the first and second generations of the tree improvement program, produced more female and male strobili than third-cycle forward selections.