VARIACIÓN EN EL PATRÓN DE ALARGAMIENTO DEL BROTE TERMINAL EN DIFERENTES PROCEDENCIAS DE Pinus engelmannii Carr.

Abstract

In arder to estímate the adaptative potential of natural populations of Pinus engelmannii to drought conditions, the level of geographic variation in seedling suNival, annual height growth and shoot phenology was evaluated in a seed sources test in Tecamac, Mexico. During the assessment period, a broad variation among populations was found both in seedling suNival, height growth rate and shoot phenology. Most populations were relatively stable in shoot growth from the first to the second year (r= 0.74), except those from Chihuahua which grew more in the second year. AII populations modified their shoot growing period from year to year, delaying the phenological events associated with initiation and termination of growth in the second year. In 1998, the growing season was almost four months long (118 days), which began on day 94 (April 4) and finished on-day 212 (July 31). Among populations the period of shoot growth varied from 107 to 127 days. The proportion of seedlings showing a second cycle of shoot growth increased from 5.5 to 55% from the first to the second year. Seedling suNival, the percentage of seedlings with a second growth cycle in the first year and shoot length of the second growth cycle in the second year, showed a variation pattern associated with the geographic origin of germplasm.