INDEXES OF MATURATION IN CONES OF PSEUDOTSUGA MENZIESII (MIRB.) FRANCO

Abstract

Douglas-fir (Pseudotsuga menziesii) is a valuable tree for Christmas tree production, and continuous seed supply is required. The southernmost limit of its natural distribution is located in México, where the appropriate window time for cone collection to obtain the best seed quality is unknown. In this research cone collections were made every 15 d, starting in late-September, on 52 trees from three natural stands of Douglas-fir with contrasting conditions in the states of Hidalgo and Tlaxcala, México. Color, relative density and moisture content of cones were evaluated as maturity criteria. Cone maturation varied across collection date. Seed weight, cone dry weight, and the relationship of these two traits did not vary significantly across dates and neither across categories of the maturity criteria. However, seed extraction from the cones was easier as cones became mature, turning from green color to brown. The seed germination capacity and velocity was also similar across collection dates or as the maturity criteria changed, with values of 22 to 30 % among locations, but the earliest collection in one location had the lowest germination percentage. For Pseudotsuga menziesii located at central México is possible to collect cones up to four weeks (late September) before seed dispersion to obtain good quality seed, even though the cost in cone processing will increase a little.