Tall trees with genes from .

CONTEXT

and are endemic to western Mexico, where they cover an area of more than 1 million hectares. is also cultivated in field trials in South Africa and South America, because of its considerable economic importance as a source of timber and resin. Seed quality, afforestation success and desirable traits may all be influenced by the presence of hybrid trees in seed stands.

AIMS

We aimed to determine the degree of hybridization between . and . in seed stands of each species located in the Sierra Madre Occidental, Durango, Mexico.

METHODS

AFLP molecular markers from samples of 171 trees across five populations were analyzed with STRUCTURE and NewHybrids software to determine the degree of introgressive hybridization. The accuracy of STRUCTURE and NewHybrids in detecting hybrids was quantified using the software Hybridlab 1.0. Morphological analysis of 131 samples from two populations of and two populations of was also conducted by Random Forest classification. The data were compared by Principal Coordinate Analysis (PCoA) in GenAlex 6.501.

RESULTS

Hybridization between and was observed in all seed stands under study and resulted in enhancement of desirable silvicultural traits in the latter species. In , only about 16% molecularly detected hybrids correspond to those identified on a morphological basis. However, the morphology of is not consistent with the molecularly identified hybrids from one population and is only consistent with 3.3 of those from the other population.

CONCLUSIONS

This is the first report of hybrid vigour (heterosis) in Mexican pines. Information about hybridization and introgression is essential for developing effective future breeding programs, successful establishment of plantations and management of natural forest stands. Understanding how natural hybridization may influence the evolution and adaptation of pines to climate change is a cornerstone to sustainable forest management including adaptive silviculture.