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

Abstract

This paper reports results obtained from microsatellite DNA analysis of genetic structure for populations of the native fungus Cronartium quercuum f. sp fusiforme infecting loblolly pine (Pinus taeda L.) over much of this host's natural range. Mostly all fusiform rust galls formed under field conditions are produced as a result of infection and colonization by haploid mycelium originating from a single basidiospore of C. quercuum fusiforme. If multiple infections do occur, then only a single haplotype must ultimately dominate and be responsible for gall formation. High levels of microsatellite variability exist in C. quercuum fusiforme and most of this variation occurs within local populations (average 88.4%). A statistically significant proportion, however, is found among populations, and the magnitude of this differentiation is closely associated with geographic distance between populations. Unweighted pair-group mean analysis and principal components analysis both indicate that at least four genetically distinct regional groups of C. quercuum fusiforme exist in the south Atlantic and Gulf coastal plains. In summary, the distribution of genetic variability in C. quercuum fusiforme is consistent with a hypothesis of at least four metapopulations with gene flow occurring less among regions than among populations within regions, and where overall levels of gene migration are related to geographic distance between populations.

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

“…The genetic diversity is high within sites (usually around 90% of the total variation) [108][109][110][111] with the remainder of the diversity present among sites. This genetic diversity is even present at a very fine scale: 70% of the total genetic diversity found within a heavily sampled plantation was found to reside among aecia within cankers [75]. This data is consistent with a high rate of outcrossing in the rust.…”

“…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].…”

“…However, there appears to be genetic structure in the pathogen population in the southeast, with at least four distinct sub-populations being detected [75]. It may be that some differences in avirulence alleles are present in these sub-populations, but that has not been determined yet.…”

Identification of Nine Pathotype-Specific Genes Conferring Resistance to Fusiform Rust in Loblolly Pine (Pinus taeda L.)

“…We recommend that the single-genotype isolates (maintained as urediniospores) be monitored with a set of informative markers such as SSRs [28,29] for the presence of contamination and that contaminated lines be subjected to the SUP protocol (Supplemental File 1) for purification. Additionally, basidiospore inocula derived from single-genotype isolates should, prior to pine inoculation, also be assessed for contamination with informative markers, and discarded if contamination is observed.…”

“…Some lines have since been re-isolated from the original lines by bulking of spores derived from a single-uredinial-pustule (see SUP protocol Supplemental File 1), with all lines subjected to SSR (simple sequence repeat) marker evaluation [28,29] to assess single-genotype purity, and to provide a DNA fingerprint for future QA/QC. The geographic origins of the five isolates used are as follows: SC20-21 is from Colleton County, South Carolina; NC2-36 and NC2-40 are from the same gall sampled in Halifax County, North Carolina; 3327-13-3 is from central Georgia in the Baldwin County area and 0-5-32 is from Greene County, Georgia.…”