Abstract
Context Pinus herrerae and P. luzmariae are endemic to western Mexico, where they cover an area of more than 1 million hectares. Pinus herrerae 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.AimsWe aimed to determine the degree of hybridization between P. herrerae and P. luzmariae in seed stands of each species located in the Sierra Madre Occidental, Durango, Mexico.MethodsAFLP 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 P. herrerae and two populations of P. luzmariae was also conducted by Random Forest classification. The data were compared by Principal Coordinate Analysis (PCoA) in GenAlex 6.501.ResultsHybridization between Pinus herrerae and P. luzmariae was observed in all seed stands under study and resulted in enhancement of desirable silvicultural traits in the latter species. In P. luzmariae, only about 16% molecularly detected hybrids correspond to those identified on a morphological basis. However, the morphology of P. herrerae is not consistent with the molecularly identified hybrids from one population and is only consistent with 3.3 of those from the other population.ConclusionsThis 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.
Highlights
Hybridization represents an important evolutionary force that can introduce much more new genetic material than is created by mutation events (Anderson, 1949; Wright, 1964)
The aim of the present study was to use Amplified Fragment Length Polymorphism (AFLP) molecular markers and morphological traits to determine the degree of hybridization between P. herrerae and P. luzmariae in seed stands of each species located in the Sierra Madre Occidental mountain system, Durango, Mexico
Samples were obtained from trees grown in three Pinus herrerae (PH) and two P. luzmariae (PL) seed stands located in the Sierra Madre Occidental, state of Durango (NW Mexico)
Summary
Hybridization represents an important evolutionary force that can introduce much more new genetic material than is created by mutation events (Anderson, 1949; Wright, 1964). It can act as an additional, perhaps more abundant, source of adaptive genetic variation than mutation (Grant & Grant, 1994), by allowing gene flow and recombination (Abbott et al, 2013; Hipp, 2018). On the other hand, increasing rates of hybridization may lead to the extinction of unique populations or species because of unsuccessful reproductive efforts or introgression with a more common species (Rhymer & Simberloff, 1996; Blanckaert & Bank, 2018). The presence of hybrid trees in seed stands ‘‘contaminates’’ the species’ gene pool and may influence seed quality and afforestation success (Arnold & Hodges, 1995; Rieseberg & Carney, 1998)
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