The effects of nursery incurred tap-root wounds on growth of Douglas-fir seedlings

Graduation date: 1987Tap-root wounds frequently occur on seedlings during lifting in\ud forest tree nurseries. Data are needed to clarify guidelines for\ud culling wounded seedlings. Two-year-old bareroot Douglas-fir\ud (Pseudotsuga menziesii (Mirb.) Franco) seedlings were wounded by hand on\ud the tap-root to lengths of either 3/8, 1, or 3 inches. Wounded\ud seedlings were used in three greenhouse experiments to determine the\ud effects of moisture stress, wound length, potentially pathogenic fungi,\ud and soil microflora on height growth, number of white root tips, root\ud dry weight, and wound closure.\ud Results indicated that, regardless of moisture stress level, wound\ud size had no significant effect on the number of white root tips and no\ud effect on height growth. However, seedlings with 1- and 3-inch wounds\ud tended, on the average, to have fewer new roots than controls or\ud seedlings with 3/8-inch wounds. Moisture stress affected wound\ud closure: seedlings with 3-inch wounds were sensitive to high soil\ud moisture and formed much callus but left some xylem still exposed;\ud smaller wounds closed almost completely under all soil moisture stress\ud levels tested. Seedling response to inoculated potentially pathogenic\ud fungi was unclear due to a bacterial problem with the fungal substrate.\ud Soil rnicroflora had no effect on seedlings with 1-inch wounds