Pinus oocarpa Schiede ex Schltdl. es una de las especies forestales en México de mayor importancia ecológica (por su amplia distribución geográfica) y económica (por la extracción de su resina en poblaciones naturales). Una resinación más intensiva requerirá de plantaciones comerciales, que podrían ser multipropósito: resina y madera. El objetivo del presente trabajo fue conocer el control genético (heredabilidad) de caracteres de crecimiento (altura total, ALT), diámetro a la base del tallo (DIAM) y diámetro a la altura del pecho (DAP), de progenies de medios hermanos de árboles originalmente seleccionados para producción de resina. Esto con la finalidad de valorar la factibilidad de un programa de mejoramiento genético multipropósito. Se estableció un ensayo de progenies en el año 2011 en Michoacán, México con 27 familias de medios hermanos en un diseño de 10 bloques completos al azar. A los cinco años después de la plantación, los promedios fueron ALT = 5.5 m, DIAM = 13.4 cm y DAP = 10.4 cm. Hubo diferencias significativas entre familias para todos los caracteres. La heredabilidad a nivel individual (h2i) fue: ALT = 0.15, DIAM = 0.22 y DAP = 0.17; a nivel media de familias (h2f) fue de 0.44, 0.54 y 0.47, respectivamente. A una intensidad de selección de mejores individuos de i=1.4, las ganancias genéticas para ALT, DIAM y DAP fueron de 3.9%, 5.2% y 5.0%, respectivamente. De demostrarse posteriormente asociación entre diámetro y producción de resina, sería factible incrementar ambos, mediante selección de individuos con mayores diámetros.

Despite the extensive distribution and use of Pinus oocarpa in Mexico, knowledge on the range of genetic variation and magnitude of quantitative parameters of the defensive structures of the species is rare. Our study attempts to fill this gap by providing a comprehensive assessment of resin duct traits in mother trees and their offsprings in an open-pollinated trial of P. oocarpa. Resin ducts are fundamental structures of the defense mechanisms of the coniferous trees. They vary depending on the age of the tree, the genotype, the species, and may be influenced by environmental factors. We investigated intraspecific variation among families of the resin duct system in secondary vascular tissues (wood and inner bark) of P. oocarpa trees. Our study attempts to explore the variance and the possible genetic control of these defensive structures. We hypothesized that the resin duct features analyzed would vary with the tree’s genetic make-up. We analyzed samples from two groups of trees. First, from mature mother trees selected as superior in resin yield. Second, from their six-year-old off-springs established in a progeny trial. Axial and radial ducts showed differences in their size and quantity, between wood and bark and between ages. The axial duct density showed differences among families, and the heritability estimates were moderate. In P. oocarpa trees selected as phenotypically superior in resin yield, the size of its constitutive resin ducts is a less variable trait, and the differences in axial duct density can be attributed to genetic factors.

Mexico ranks 5th in worldwide resin production. Pinus oocarpa is the most widely tapped pine tree in Mexico. Michoacán (central-western Mexico) is the first nationwide state producer of resin. Despite the P. oocarpa relevance, there is no genetic improvement program in the country for resin production. We evaluated the degree of genetic control for growth, anatomical traits, resin yield, and the correlation among them at an early age (five-years-old for growth, six for resin, and anatomical traits) in a P. oocarpa half-sib progeny trial. Families were originated from selected mother trees, based on their resin yield. We found significant genetic variation among families for stem volume (h 2 i = 0.12, h 2 f = 0.35), traumatic ducts (diameter: h 2 i = 0.63, h 2 f = 0.51; area: h 2 f = 0.81), and resin yield (individual and family narrow-sense heritability: h 2 i = 0.20, h 2 f = 0.52), and a positive correlation between diameter and area of traumatic ducts with resin yield (Pearson correlation: r= 0.73, p= 0.04; r= 0.71, p= 0.0497; respectively). Results suggest that the early selection (six-years-old) of superior P. oocarpa families, based on resin yield (estimated by microchipping technique), and/or based on larger diameter and area of traumatic ducts, appears to be a feasible strategy to develop seed orchards able to provide genetically improved seeds for intensive resin tree plantations. That would be an important alternative for a state as Michoacán, Mexico, where natural P. oocarpa stands are being replaced for avocado orchards for exportation.

No abstract