Occurrence of Kabatina juniperi in Ontario and genetic analysis using RAPD markers

Abstract

A survey conducted in 1992 and 1993 revealed that the major cause of juniper twig blight in Ontario was Kabatina juniperi. Phomopsis juniperovora was found in 3 of 26 samples received in 1992 and in none of 23 samples in 1993. Analysis of acervuli of K. juniperi collected from spring 1997 through spring 1999 showed that spore production was high in spring, was lower in the summer, and gradually declined in the fall to very low levels in winter. Using RAPD markers, we found molecular variation between K. juniperi isolates from five locations within a 50 km radius. RAPD analysis of 24 isolates from five different cultivars of Juniperus scopulorum did not reveal host specialization. Among 49 isolates sampled from two adjacent rows of J. scopulorum ‘Grey Gleam’, there were 36 different RAPD haplotypes. Genetic diversity analysis of this population showed significant gametic linkage disequilibrium between putative RAPD loci and indicated that asexual propagules such as conidia are the major form of dispersal of this pathogen. A practical implication of this work is that pruning operations should be timed so that they do not coincide with peak spore production.

Keywords:

• population genetics
• epidemiology
• molecular ecology