Fine-Level Genetic Structure of White Pine Blister Rust Populations

Abstract

The fine-level genetic structure of the white pine blister rust agent, Cronartium ribicola, was investigated by sampling multiple monokaryotic spermogonia directly on cankers in four eastern Canadian white pine (Pinus strobus) plantations and assessing genetic variability, using random amplified polymorphic DNA (RAPD) markers. Ninety-eight percent of the cankers surveyed contained a single DNA haplotype, suggesting spermogonia within cankers are the result of clonal reproduction. A single canker contained two haplotypes that were divided between the upper and lower parts of the canker, suggesting it represented two confluent cankers. In contrast, genotypic diversity was high among cankers. Thirty-seven haplotypes were found among forty-three cankers sampled, and an analysis of molecular variance indicated that 93% (P < 0.001) of the total genetic diversity was attributable to sampling of different cankers, strongly suggesting that multiple infections do not take place in the white pine blister rust pathosystem, i.e., a canker is the result of infection by a single genotype. This result is in contrast with the high level of genetic diversity previously reported among dikaryotic aecidia within cankers and is consistent with the hypothesis that variability in the aecidial stage is the result of outcrossing between resident spermogonia and alien spermatia. The genetic structure of the spermogonial stage, which is the vegetative extension of infection by basidiospores and, therefore, the indirect result of meiosis, was consistent with random mating; the observed genotypic diversity was not significantly different (P > 0.05) from the genotypic diversity expected under the assumption of panmixis. The results indicate that monokaryotic cankers can be genotyped by sampling a single unopened spermogonia per canker.

Microsatellite DNA suggests regional structure in the fusiform rust fungus Cronartium quercuum f. sp fusiforme

“…Therefore, differentiation among local populations within regions could not be distinguished from variation among individual galls within populations. Similar observations of large withinpopulation variability have been reported for eastern Canadian populations of white pine blister rust fungus, C. ribicola (Hamelin, 1996;Hamelin et al, 1998;Et-touil et al, 1999). As a general conclusion, C. quercuum fusiforme exists as a highly variable formae speciales, with a large proportion of its genetic variability occurring within populations.…”

“…Unlike C. quercuum fusiforme, C. ribicola is an exotic pathogen in North America, having been separately introduced to both eastern and western portions of this continent early in the 20th century (Maloy, 1997). Investigations in eastern Canada and in western North America based on neutral genetic markers indicate that most genetic diversity in this fungus is found among individual infections within local populations, but that modest differentiation also occurs among populations within geographic regions (Hamelin et al, 1995(Hamelin et al, , 1998Kinloch et al, 1998;Et-touil et al, 1999). Furthermore, there is no evidence for genetic variability among population composites representing different regions within either eastern or western areas.…”

Genetic Resistance to Fusiform Rust in Southern Pines and White Pine Blister Rust in White Pines—A Contrasting Tale of Two Rust Pathosystems—Current Status and Future Prospects

“…This data is consistent with a high rate of outcrossing in the rust. Spermatization, the process whereby insects carry the spermatia between cankers, creates highly variable genetic mosaics in pine rust cankers [75,[111][112][113]. Extensive recombination was detected among haploid spermogonia sampled within populations [114].…”

New genetic markers for identifying Cronartium flaccidum and Peridermium pini and examining genetic variation within and between lesions of Scots pine blister rust in Sweden

“…A mosaic genotype pattern has also been shown in lesions of Cronartium ribicola, where more than one RAPD profile was present in aecia of the same lesion (Hamelin 1996), indicating outcrossing in this species. When unopened (and thus unfertilized) spermogonia within lesions of C. ribicola were analyzed (Hamelin et al 1998), they contained the same genotype. This would be consistent with a single resident mycelium within a lesion.…”