GENETIC VARIATION AMONG Pinus patula POPULATIONS ALONG AN ALTITUDINAL GRADIENT. TWO ENVIRONMENT NURSERY TESTS

Aiming to determine if there is genetic differentiation among Pious patula Schiede et Chamizo populations along an attitudinal gradient and for quantifying the genotype x environment interaction, 13 Pious patula populations were sampled from forests of the Native Indian Community of Ixtlan de Juarez, Oaxaca, state of Mexico, along an attitudinal gradient (2400 m to 3000 m), cones being collected on groups of trees on every 50 m of attitudinal step). Seedlings were grown in tree pots in two different environments: a shadehouse located at Ixtlan de Juarez, and in a greenhouse and then in a shadehouse situated at Quebec, Canada. Total seedling height was measured at 6-months of age in both locations. Results indicated that populations differed significantly (P = 0.025), but there was no significant genotype x environment interaction (P = 0.426; B type genetic correlation = 0.93). Population from 2650 m (middle altitude) exhibited the best height. Although not definitive, our study suggests the presence of a weak attitudinal pattern of variation in seedling height, where populations originating of mid-altitudes exhibit the highest growth potential while populations from the upper and lower attitudinal extremes exhibit the lowest growth potential.