Winter sowings produce 1-0 sugar pine planting stock in the Sierra Nevada

Abstract

Seed source and sowing date effects on first-year seedling growth and Fusarium root and collar rot of sugar pine were analyzed in two consecutive nursery tests at the Pacific Southwest Research Station's Institute of Forest Genetics, near Placerville in the western Sierra Nevada. The experimental design in both tests consisted of four replications of a randomized complete block of split-split plots, with sowing date split for disease treatment and seed source. Seed sources were natural stands at low, middle, and high elevations on the western slope of the northern Sierra Nevada. Seeds were soaked 36 hours in aerated water at 25° C (77° F), chilled 90 days at l°C (34° F), and sown in fumigated soil in February, March, April, and May. Treatment plots were drenched with ungicides just before sowing in the first test, and were inoculated with Fusarium oxysporum f. sp. pini at time of sowing in the second test. Seedling emergence averaged 96 to 99 percent, regardless of sowing date. Seedlings in February sowings reached triple the size of those in the traditional May sowings, and mortality in the check and inoculated plots averaged 3 and 6 percent in the February sowings, against 17 and 33 percent in the May sowings. The results show that seedlings in early sowings (February, March) consistently escape Fusarium disease and produce 1-0 planting stock. Those in late sowings are highly susceptible to Fusarium and the survivors must be carried through a second growing season to produce 2-0 planting stock.