Genetic variation in selected acorn and seedling characteristics of northern red oak (Quercus rubra L.).

Three separate studies were conducted to evaluate genetic variation in selected acorn and seedling characteristics of northern red oak (Quercus rubra L.) and white oak (Quercus alba L.). The objective of the studies were to: (1) evaluate sources of genetic variation and genotype-environmental interaction in seedling characteristics, (2) determine occurrence and frequency of polyembryony within and among half-sib families of northern red oak and relationships between acorn size and polyembryony, and (3) determine the maximum length of time northern red oak acorns can be left under simulated orchard conditions and collection procedures and remain viable.

For the first objective, seedlings from 12 genetic families of both species were grown at locations in Tennessee and Georgia. White oak was found to be very sensitive to early growing season water stress that occurred at the Tennessee location, causing cessation of seedling growth following initial germination and growth. Following increased soil moisture levels, the seedlings generally failed and set a terminal bud to recommence growth and development. The northern red oak seedlings were subjected to the same water stress, but responded to the increase in soil moisture levels. However, the seedlings failed to reach the same size as the other location. Northern red oak families exhibited wide variation between family means. A distribution analysis on number of first-order lateral roots, indicated that most seedlings will fail to meet minimum standards for planting on highly competitive upland sites. Single tree and family heritability estimates for growth characteristics were relatively similar at both locations and generally lower than combined location estimates.

Acorn germination and dissections were used to determine the occurrence of polyembryony in eight open-pollinated families of northern red oak. Relationships between acorn size and polyembryony was determined between collections of two mother trees. Only seed sources from Overton County, Tennessee, produced polyembryonic acorns. Acorn germination tests revealed more embryos per acorn than acorn dissections. As acorn size increased, the number of embryos increased in families predisposed to polyembryony. The occurrence of polyembryony in northern red oak open pollinated families indicated that seed sources should be screened for polyembryony occurrence.

A two year study of the relationship between acorn moisture content, weather and the number of days following natural seed fall under simulated orchard conditions. Northern red oak acorns were collected from 10 trees and were subjected to five levels of shading for a thirty day period and at two day intervals, acorn moisture content was determined. It was found that acorn moisture content did not desiccate below 25 percent under all shading regimes, indicating that viability was not affected. Results of the experiment generally indicated that other factors such as predation should be of greater importance to overall viability of acorn crops than acorn desiccation.