First Report of Quinoa Downy Mildew Caused by <i>Peronospora variabilis</i> in the United States
Bibliographic record
Abstract
Quinoa, Chenopodium quinoa Willd., is an Andean crop prized for its high nutritional value and adaptability to harsh environments. Quinoa is plagued by downy mildew caused by Peronospora variabilis Gäum (formerly Peronospora farinosa f. sp. chenopodii Byford) (1). Quinoa production has spread beyond native Andean ranges and quinoa downy mildew has been reported in India, Canada, and Denmark (1). During the summer of 2011, quinoa trials were established to determine the ability of quinoa to grow under Mid-Atlantic conditions and monitor for regional disease problems. In July, after cool, rainy conditions, downy mildew-like symptoms were observed on quinoa at research plots in Centre and Lancaster counties of Pennsylvania. Symptoms and signs consisted of irregularly shaped areas of foliar chlorosis or pink discoloration accompanied by dense, gray sporulation on both leaf surfaces. Sporangia were tan to gray-brown, semi-ovoid, often with a pedicel, mean length of 31 μm, and mean width of 23 μm. Sporangiophores branched dichotomously, and the terminal branchlets curved and tapered to a point. Orange oospores were present in field samples of leaf tissue. DNA was extracted from infected foliar tissue and sporangial suspensions. A seminested PCR protocol (2) was used to obtain partial internal transcribed spacer (ITS) sequences of six Peronospora isolates. The sequences shared 99% maximum identity to a known P. variabilis accession (FM863721.2) in GenBank. A voucher specimen was deposited into the U.S. National Fungus Collections (BPI 882064). Pathogenicity of each of two strains of P. variabilis was confirmed by inoculating quinoa with sporangia (4). Sporangia were shaken from leaves in sterile distilled water and the suspension was filtered through cheesecloth. A 0.01% Tween solution was added and the suspension diluted to 10 3 sporangia/ml. With an atomizer, a 10-ml sporangial suspension (or sterile water for noninoculated control plants) was sprayed onto one flat of 18 2-week-old quinoa plants, and relative humidity was increased to saturation using a humidity dome for 24 h. After 1 week, chlorosis and pink discoloration were noted on leaves of inoculated quinoa, and after 18 h of subsequent increased humidity (>95% relative humidity), dense gray sporulation was observed. No symptoms were noted on noninoculated control plants. Sporangia and sporangiophores were examined morphologically and confirmed to be P. variabilis, confirming Koch's postulates. For culture maintenance, 2-week-old quinoa leaves were placed onto a sporangial suspension on top of 1% water agar and maintained in a growth chamber at 20°C with 16 h of light per day. Quinoa downy mildew is seedborne (3) and initial infections may have occurred from oospores in the pericarp, despite intensive processing of consumable quinoa seeds to remove saponins. To our knowledge, this is the first report of quinoa downy mildew in the United States and also the first report of P. variabilis in the United States. References: (1) Y. Choi et al. Mycopathologia 169:403, 2010. (2) D. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) S. Danielson et al. Seed Sci. Technol. 32:91, 2004. (4) J. Ochoa et al. Plant Pathol. 48:425, 1999.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".