White Oak Epicotyl Emergence and 1-0 Seedling Growth from Surgically Altered Germinating Acorns

Open-pollinated white oak (Quercus alba L.) acorns were collected and stored at 4 °C in November 2004. Three days before sowing in early December, we treated germinating acorns in fi ve ways: no surgery (C); one half of the radicle cut off (HR); whole radicle cut off (WR); one cotyledonary petiole severed (OP); and both cotyledonary petioles severed, which resulted in no embryo axis (NE). Seedlings were lifted in February 2006. The NE treatment had two percent epicotyl emergence and was not included in our statistical analysis. The OP seedlings were shorter and had greater root-to-shoot ratio than seedlings in other treatments. For most of the families, the OP treatment had less percent epicotyl emergence; OP seedlings also had smaller root collar diameter and less biomass than C. More HR and WR seedlings had a forking root system than C. Our study showed that white oak acorns should be sown before radicle protrusion to avoid damage, which may reduce growth or result in loss of the epicotyl. 1Research Plant Physiologist, U.S. Forest Service, Southern Research Station, Pineville, LA; Principal Silviculturist Emeritus, U.S. Forest Service, Southern Research Station, Athens, GA; Research Mathematical Statistician, U.S. Forest Service, Southern Research Station, Asheville, NC, respectively. INTRODUCTION White oak (Quercus alba L., WO) is among the most valuable and abundant oak species in the Eastern United States. It often coexists with northern red oak (Q. rubra L.) in natural stands. The number of both species is declining, and their prominence on high-quality mesic sites has diminished throughout their ranges due to lack of adequate natural regeneration. Artifi cial regeneration of oaks has not been successful on those sites due to severe competition from faster growing or more shade tolerant species. The absence of quality oak planting stock is another reason given for the regeneration failure (Kellison 1993, Lorimer and others 1994). Since the early 1990s, scientists and staff officers from the USDA Forest Service Southern Research Station, Southern Region, and the Georgia Forestry Commission have developed and implemented an integrated artifi cial oak regeneration program. The program’s purpose is to establish oak seedling plantings on several national forests in the Southeastern United States, in order to meet land management goals and objectives (Kormanik and others 1994, 2000, 2002, 2006). The goal of an integrated regeneration program is to establish seed-production areas, to obtain desirable stocking in reforestation areas, and to augment species composition in such areas. Attributes of successful oak stand establishments are good survival, fast growth, and early acorn production. Growing and selecting the bareroot oak seedlings that possess the most desirable root system and stem characteristics, as well as protecting planted stands from competition for several years after establishment, will help ensure success (Clark and others 2000, Kormanik and others 1997, 2002, 2004, 2006). A full cycle of this artifi cial regeneration program begins with acorn collection, handling, and storage. The next phases in the program include growing, grading, and outplanting seedlings, as well as selecting, preparing, and maintaining sites. Such a program results in fully stocked oak stands that can be used for timber, wildlife, or aesthetic purposes, as well as sites from which to collect acorns for future stands (Kormanik and others 2006). Among many successful applications of this regeneration program, however, some failures also came to light. In some cases the lack of effective and timely vegetationcontrol regimes in planted stands may have caused stand establishment failures (Kormanik and others 2004, 2006). Sometimes, due to errors in acorn collection and storage prior to sowing, the entire seedling crop was discarded at the nursery. This was especially true with WO (Kormanik and others 2000, Sung and others 2002, 2006). White oak acorn germination is highly sensitive to acorn desiccation (Connor and Sowa 2003, Sung and others 2006), and WO acorns with less than 30 percent moisture content had less than 12 percent germination (Sung and others 2006). Nevertheless, WO acorn moisture contents at sowing did not affect subsequent seedling growth in the study by Sung and others (2006). Factors other than low acorn moisture contents at sowing must be contributing to poor WO seedling growth in the nursery (Kormanik and others 1997, Sung and others 2002). Unlike the red oak species group, acorns from the white oak species group do not need stratifi cation to germinate. It is commonly observed that WO acorns germinate during storage at 4 °C. After the radicle extends, the germinating WO acorn extends its cotyledonary petioles out of the acorn fruit pericarp between which the epicotyl (future shoot) eventually extends. The protruding parts of the germinating acorns are vulnerable to physical damage during acorn storage, handling and sowing. Our study objective is to evaluate the effects that varying degrees of physical damage to the radicle and the cotyledonary petioles of WO acorns prior to sowing have on epicotyl emergence and subsequent seedling growth. MATERIALS AND METHODS Preliminary Study White oak acorns were collected from a mother tree in Athens, GA within 24 hours after dropping. The acorns were soaked in water for 30 minutes. All fl oating acorns and Citation for proceedings: Stanturf, John A., ed. 2010. Proceedings of the 14th biennial southern silvicultural research conference. Gen. Tech. Rep. SRS-121. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 614 p.