Document: ZHO-3-42-28

Allozyme variation is associated with Douglas-fir phenotypic resistance to western spruce budworm defoliation.

CHEN, Z.* ¹, T.EKOLB ¹, K.MCLANCY ², L.EDEWALD ¹ and V.DHIPKINS ³

Northern Arizona University, Flagstaff, AZ 86011 USA ¹
USDA Forest Service, Flagstaff, AZ 86001 USA ²
USDA Forest Service, CA 95709 USA ³

Abstract:
The objective of this study is to determine if genetic variation in inland Douglas-fir Pseudotsuga menziesii populations is associated with trees showing phenotypic resistance to western spruce budworm Choristoneura occidentalis defoliation. Douglas-fir seeds collected from 20 putatively resistant and 16 putatively susceptible mature trees that differed in crown damage after heavy budworm outbreaks in Colorado and Arizona were used to analyze the allozyme variation with electrophoresis techniques. Within each site, phenotypically resistant and susceptible trees were within a pollinating distance of each other. Ten megagametophytes per tree were used and 25 loci were analyzed with three buffer systems: lithium borate (pH 8.3), sodium borate (pH 8.8), and morpholine citrate (pH 6.1). The mean number of alleles per polymorphic locus was 2.47 0.15, and 2.60 0.16, in resistant and susceptible trees, respectively. A difference in allele frequency between phenotypically resistant and susceptible trees occurred in loci LAP-2, PGI-2, PGM-1, ACO-2, MDH-1, UGPP-1, and UGPP-3. In addition, susceptible trees had a significantly higher mean overall allele heterozygosity (0.214 0.047) than resistant trees (0.177 0.042) (p = 0.0197). These results support the hypothesis that phenotypically resistant and susceptible trees differ genetically, but do not support the fitness hypothesis that resistant trees would have higher allele heterozygosity. Since budworm defoliation plays a dominant role in the ecological and genetic processes of Douglas-fir population, natural selection may favor Douglas-fir with higher homozygosity.

Keywords: ALLOZYME, ELECTROPHORESIS, RESISTANCE, DEFOLIATION

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS