Quantifying the geographic range of Pinus patula var. longipedunculata in Southern Mexico using morphologic and RAPD marker data: scientific paper

Abstract

Pinus patula var. longipedunculata occurs in southern Mexico, but the extent of its geographic range is poorly defined. Trees from some populations are morphologically similar to P. tecunumanii , which adds to the confusion over the variety's geographic range. Recent field explorations have identified six new populations of supposed P. patula var. longipedunculata in the Sierra Madre del Sur of Oaxaca and Guerrero. In an effort to determine the validity of these sightings, botanical samples were collected from 79 trees in these six populations and were assessed for ten cone and needle morphology traits. Random Amplified Polymorphic DNA (RAPD) analyses were conducted on 73 trees from the six populations, 38 of which were in common to 79 trees used in the botanical study. Species control lots for both the botanical and RAPD studies were P. herrerae, P. oocarpa, P. patula, P. pringlei and P. tecunumanii. Morphologic assessment indicated trees in the Manzanal population were predominantly patula -related, but trees in the other five populations grouped into two clusters that were significantly different from P. patula and P. tecunumanii and not strongly related to the other control species. Conversely, molecular marker results indicated that four of the populations, Manzanal, San Mateo, Tlacuache (Oaxaca) and Yextla (Guerrero) were genetically indistinguishable or closely related to P. patula. The remaining two populations, Juquila (Oaxaca) and Palo Blanco (Guerrero), were closely related genetically to P. herrerae / P. pringlei. The morphologic study indicated that 5% of the trees in the six populations were indistinguishable from P. tecunumanii, but marker analyses indicated that the trees in question were of either P. patula or P. herrerae / P. pringlei origin. Pinus tecunumanii does not appear to occur in the Sierra Madre del Sur of Oaxaca and Guerrero, but a four-needle type of P. herrerae that can be very easily confused with P. patula var. longipedunculata does. The geographic range of P. patula var. longipedunculata is defined as occurring from northeastern Oaxaca to central Guerrero. The existence of populations of the variety in Chiapas needs to be verified using molecular techniques. The genetic relationship between P. pringlei and P. herrerae is much closer than heretofore thought, even though the morphology of each species is very distinctive.


Southern African Forestry Journal No.192 2001: 19-30