Stock-scion relationships and graft incompatibility in slash pine and loblolly pine

Abstract

The failure to form an adequate union between the scion and rootstock was found to be the greatest cause of first-year graft failure. Other causes of death were relatively insignificant. Grafting losses could be expected throughout the first growing season, although a majority of graft failures occurred prior to 120 days from grafting. In a study involving clonal interstocks, scion material influenced the survival of the graft, while the interstock influenced scion growth during the first year following grafting. Loblolly scion material grafted onto loblolly and slash rootstocks resulted in certain rootstock sources producing a greater amount of scion growth. Mo differences between rootstock species were observed. Early results showed no graft incompatibility when grafts between related and unrelated individuals were made. However, scion growth was poorest on unrelated rootstocks. In an established slash pine seed orchard, compatible ramets produced a much greater number of cones, seeds, and filled seeds. The seeds produced by compatible ramets was also much heavier, and resulted in more seedling growth after one year in the nursery. The correlation between ortet specific gravity and graft survival indicated that specific gravity could not be used to predict grafting success. Nursery grown rootstock resulted in much better scion growth than did woods grown rootstock. No differences occurred among scion clones or interstock clones for graft incompatibility during the second growing season, and pruning of grafts did not increase the amount of incompatibility observed. The major conclusion was that scion performance varies with the type of rootstock, and the use of known genotypes as rootstock may be one method of improving scion development and reducing graft incompatibility.