ALTITUDINAL GENETIC VARIATION AMONG P. OOCARPA POPULATIONS ON MICHOACAN, WESTERN MEXICO. PRELIMINARY RESULTS FROM A NURSERY TEST

摘要

We are investigating if there is genetic differentiation among natural populations of Pinus oocarpa along altitudinal gradients. Open pollinated seeds from about eleven individual trees were collected from each of five Pinus oocarpa natural populations distributed along an altitudinal gradient from 1100 to 1500 m, near to Uruapan city, Michoacan state, western Mexico. A provenance/progeny test was established in a nursery and evaluated from 1 to 9 months of age. Genetic differentiation among populations was in general weak, significant only for number of cotyledons and nearly significant (p = 0.076) for 6-month-old diameter, and not significant for the rest of the examined variables: length of the longest cotyledon, height at 2, 6 and 9 months of age and diameter at 9 months of age. However, variance among half-sib families within populations was significant for all traits and ages. Number of cotyledons shows a clinal pattern, where in general average number of cotyledons is larger in populations from lower altitudes, and smaller in populations from higher altitudes. Diameter at 6 months of age shows an altitudinal variation pattern similar to a normal curve, where populations from the middle of the species altitudinal range show an "optimum" growth -having the largest diameter- and populations at the upper and lower extremes of the altitudinal range show the lowest diameters.