Introgression between Pinus taeda L. and Pinus echinata Mill

Loblolly pine (Pinus taeda L.) and shortleaf pine (Pinus echinata Mill.) have widely overlapping geographic ranges. Hybridization between the two species has interested tree breeders for a long time. Morphologically, the two pine species are different. The needles of loblolly pine are 6 to 9 inches long, usually with three yellow-green needles per fascicle; but shortleaf pine needles are 3 to 5 inches long, with two or three dark yellowgreen slender and flexible needles per fascicle. Loblolly pine also has larger cones than shortleaf, as well as other differences, however, these characters offer limited help when the genotypes of the parents and their probable hybrids are compounded by environmental factors The limitations of morphological characters resulted in the identification of the allozyme marker IDH (isocitrate dehydrogenase) to identify hybrids (Huneycutt and Askew, 1989). The high frequency of IDH variation seen in natural shortleaf pine populations outside the natural range of loblolly pine (Rajiv et al., 1997) suggests either profuse hybridization between the two species or that IDH is an unreliable marker. These data required us to look for new markers to confirm the identity of putative hybrids.