First Report of Black Root Rot Caused by <i>Thielaviopsis basicola</i> on Soybean (<i>Glycine max</i>) in Arkansas
Bibliographic record
Abstract
Thielaviopsis basicola (Berk. & Broome) Ferraris (synonym Chalara elegans Nag Raj & Kendrick) is a soilborne plant-pathogenic fungus reported in many parts of the world. In Arkansas, T. basicola is found commonly in cotton fields (4). This fungus colonizes cortical tissue of seedlings under cool wet conditions, causing a dark brown or black discoloration of the roots and hypocotyls, resulting in stunted, slow-developing plants (4). In 2008, large areas of stunted soybean plants with shortened internodes were reported in a field in Phillips County, AR, where cotton had previously been produced. Soybean was planted in this field in early April when cool soil temperatures (~21 to 24°C) prevailed. Soybean plants at the v3 to v5 growth stages were observed to have extensive areas of black cortical root necrosis. Plant samples were collected and roots were excised, washed, and surface disinfested in a 10% NaOCl solution. Root segments were incubated on the carrot-based selective medium TB-CEN (3). T. basicola was isolated from incubated segments after 2 weeks at 21°C in the dark. Chlamydospore chains (44.8 to 56.0 × 8.4 to 11.2 μm) consisting of an average of six spores and endoconidia (8 to 30 × 3 to 5 μm) were observed with a compound microscope. In addition to plant tissue, soil was assayed and confirmed to be positive for T. basicola by the pour plate technique (3) with the medium TB-CEN. Greenhouse trials were conducted to confirm field observations. Soil from the Phillips County field was sterilized and reinfested with 100 CFU of chlaymdospore suspension per gram (dry weight) of soil. Fifty soybean seeds (cv. Schillinger 457) were planted in infested and sterilized soil and grown for 29 days. Results showed that 38% of plants germinated and survived in the T. basicola-infested soil compared with 71% in the sterile soil treatment. Fifteen of the nineteen plants that survived in the infested soil were positive for T. basicola, while all plants in the sterilized soil were negative for the fungus. Soybean has previously been reported to be a host of T. basicola worldwide, but North American reports have been confined to Canada and Michigan, where cool soil temperatures persist for longer periods during the early part of the growing season (1,2). To our knowledge, this is the first report of T. basicola being important in the growth of soybean in warmer latitudes where the pathogen has been observed frequently on cotton and tobacco. In areas where cotton has historically suffered seedling damage from T. basicola, black root rot may become important on soybean as production of the latter crop increases. Since the initial field observation and confirmation in 2008, multiple soybean fields in 10 Arkansas counties have been documented with black root rot, with an estimated 5 to 30% of plants in each field infected. References: (1) T. R. Anderson. Can. J. Plant Pathol. 6:71, 1984. (2) J. L. Lockwood et al. Plant Dis. Rep. 54:849, 1970. (3) L. P. Specht and G. J. Griffin. Can. J. Plant Pathol. 7:438, 1985. (4) N. R. Walker et al. Phytopathology 89:613, 1999.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 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".