Genetics of allozyme variants in loblolly pine

Abstract

Allozyme variants in 10 enzyme systems are encoded by at least 17 loci, using megagametophytes and embryos of wind-pollinated and control-crossed families of loblolly pine (P. taeda L.) seed from seed orchard clones. The segregation of allozymes in megagametophytes of heterozygous clones reveals that the single zone of activity on gels stained for glutamate dehydrogenase (GDH) and 6-phosphogluconate dehydrogenase (6PGD) is each controlled by a single locus. The segregation of allozymes in 2 zones of activity for leucine aminopeptidase (LAP), phosphoglucose isomerase (PGI), phosphoglucomutase (PGM) and glutamateoxaloacetate transaminase (GOT) shows that 2 loci control each of these enzymes. A 3rd locus, coding GOT variants, seems to be active only in embryos. Acid phosphatase (AP) and malate dehydrogenase (MDH) reveal 2 zones of activity. In the lower zone of both of these enzymes, single-banded variants occur in megagametophytes and allozyme segregation supports single-locus control for each. The upper zone of AP, segregating for both single- and double-banded variants, may also be controlled by a single locus. The upper zone of MDH, as well as the single zones of activity observed for aconitase and isocitrate dehydrogenase were each invariant for a single band, but indirect evidence inferred from studies in the closely related pitch pine suggests single-locus control for each. In 8 loci where embryo band patterns could be interpreted, the same locus coded for allozymes in embryos and megagametophytes. Embryo expression in MDH and GOT demonstrate that a gene may not necessarily be detectable in both tissues. Segregation distortions were observed for 3 heterozygous combinations, and in each case, the deficiency of a particular allele was consistent over several parents.