Provenance Impacts Transplant Establishment and Adventitious Root Regeneration of Sycamore

A series of six experiments was conducted over eight years to investigate impacts of provenance on transplant establishment in landscapes and the role of adventitious root regeneration in differential genotypic responses during establishment of Platanus occidentalis L. Fall, spring, and summer transplants of container-grown half-sib families (HSF = seedlings derived from a single mother tree with unknown male parentage), including two selections native to Brazos County, Texas (Brazos-C, Brazos-D), one native to Cookeville, Tenn. (Cookeville), two Kentucky/Tennessee HSF from the Westvaco Corp. (WV-10, WV-14), and two Texas HSF from the Texas Forest Service tree improvement program (TFS-09, TFS-24), were established to determine field/landscape growth responses. Subsequent studies were conducted to investigate differential leaf gas exchange responses of TFS-09 and Cookeville during moderate water deficits and to determine root regeneration potential (RRP) responses of TFS-09, Brazos-C, WV-14, and Cookeville HSF following fall, spring, and summer transplant. To investigate consistency of within-family genotypic responses and to determine relationships among adventitious root initiation from shoot cuttings, RRP, and landscape establishment, five seedlings of TFS-09 and five from Cookeville HSF were clonally propagated and ramets tested under field and RRP conditions similar to those with seedling-derived plants. Regionally native HSF consistently grew taller, had larger trunk diameters, and often had greater survival during the first 3 years in the landscape than HSF not native to the region in which the studies were conducted. Rapidity of root regeneration among HFS at the time of transplant was the best root growth related predictor of successful landscape establishment. Some growth advantages were found using genetically improved HSF, but not as consistent an improvement as with the use of seedlings from regional provenances. Within-family variation in landscape performance was greater with nonregional Cookeville clones than with regional TFS-09 clones, however there was overlap among the more vigorous Cookeville clones and the least vigorous TFS-09 clones. Increased rapidity of root regeneration and drought adaptations related to leaf morphology and gas exchange characteristics may be involved in enhanced growth responses of Texas regional genotypes. No consistent relationships were found among adventitious rooting responses from shoot cuttings and subsequent RRP of the same genotypes from root tissues or their growth during the first 3 years in landscapes.

Restoration of high adventitious root regeneration potential in mature Betulapapyrifera Marsh, softwood stem cuttings

Grafted mature (flowering) Betulapapyrifera Marsh, scions were used to investigate restoration of high adventitious root regeneration potential in softwood stem cuttings. Scion manipulation (defoliation), serial propagation (using previously rooted cuttings as stock plants), hedging (severe pruning), and micropropagation were used as possible restoration treatments. Over a 15-month period, more than 8000 softwood stem cuttings were taken for propagation. Serial propagation more than doubled (from 20 to 44%) rooting response. Rooting response of tissue cultured microcuttings resulting from adventitious shoot initiation averaged 95% for 35 clones. By comparison, rooting response of open pollinated seedling families was 87% and stem cuttings from stock plants grown from tissue cultured microcuttings averaged 75%. Variation in clonal rooting response among propagation times represented a greater source of variation than that attributed to serial propagation or clone. Scion manipulation and hedging were ineffective in increasing stem cutting rooting potential. High rooting potential in mature birch can best be restored via tissue culture.