Sources of genomic diversity in the self-fertile plant pathogen, <i>Sclerotinia sclerotiorum</i> , and consequences for resistance breeding
Bibliographic record
Abstract
Abstract The ascomycete, Sclerotinia sclerotiorum , has a broad host range and causes yield loss in dicotyledonous crops world wide. Genomic diversity and aggressiveness were determined in a population of 127 isolates from individual canola ( Brassica napus ) fields in western Canada. Genotyping with 39 simple sequence repeat (SSR) markers revealed each isolate was an unique haplotype. Analysis of molecular variation showed 97% was due to isolate and 3% to geographical location. Testing of mycelium compatibility identified clones of mutually compatible isolates, and stings of pairwise compatible isolates not seen before. Importantly, mutually compatible isolates had similar SSR haplotype, in contrast to high diversity among incompatible isolates. Isolates from the Province of Manitoba had higher allelic richness and higher mycelium compatibility (61%) than Alberta (35%) and Saskatchewan (39%). All compatible Manitoba isolates were interconnected in clones and strings, which can be explained by wetter growing seasons and more susceptible crops species both favouring more mycelium interaction and life cycles. Analysis of linkage disequilibrium rejected random recombination, consistent with a self-fertile fungus and restricted outcrossing due to mycelium incompatibility, and only one meiosis per lifecycle. More probable sources of genomic diversity is slippage during DNA replication and point mutation affecting single nucleotides, not withstanding the high mutation rate of SSRs compared to genes. It seems accumulation of these polymorphisms lead to increasing mycelium incompatibility in a population over time. A phylogenetic tree grouped isolates into 17 sub-populations. Aggressiveness was tested by inoculating one isolate from each sub-population onto B. napus lines with quantitative resistance. Results were significant for isolate, line, and isolate by line interaction. These isolates represent the genomic and pathogenic diversity in western Canada, and are suitable for resistance screening in canola breeding programs. Since the S. sclerotiorum life cycle is universal, conclusions on sources of genomic diversity extrapolates to populations in other geographical areas and host crops. Author summary Sclerotinia sclerotiorum populations from various plant species and geographical areas have been studied extensively using mycelium compatibility tests and genotyping with a shared set of 6-13 SSR markers published in 2001. Most conclude the pathogen is clonally propagated with some degree of outcrossing. In the present study, a population of S. sclerotiorum isolates from 1.5 million km 2 area in western Canada were tested for mycelium compatibility, and genotyped with 9 published and 30 newly developed SSR markers targeting all chromosomes in the dikaryot genome (8+8). A new way of visualizing mycelium compatibility results revealed clones of mutual compatible isolates, as well as long and short strings of pairwise compatible isolates. Importantly, clonal isolates had similar SSR haplotype, while incompatible isolates were highly dissimilar; a relationship difficult to discern previously. Analysis of population structure found a lack of linkage disequilibrium ruling out random recombination. Outcrossing, a result of alignment of non-sister chromosomes during meiosis, is unlikely in S. sclerotiorum , since mycelium incompatibility prevents karyogamy, and compatibility only occur between isolates with similar genomic composition. Instead, genomic diversity comprise transfer of nuclei through hyphal anastomosis, allelic modifications during cell division and point mutation. Genomic polymorphisms accumulate over time likely result in gradual divergence of individuals, which seems to resemble the ‘ring-species’ concept. We are currently studying whether nuclei in microconidia might also contribute to diversity. A phylogenetic analysis grouped isolates into 17 sub-populations. One isolate from each sub-population showed different level of aggressiveness when inoculated onto B. napus lines previously determined to have quantitative resistance to a single isolate. Seed of these lines and S. sclerotiorum isolates have been transferred to plant breeders, and can be requested from the corresponding author for breeding purposes. Quantitative resistance is likely to hold up over time, since the rate of genomic change is relatively slow in S. sclerotiorum .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".