Cotton (Gossypium hirsutum L.) is among the most commonly cultivated cash commodities in Türkiye. It is vital to both the textile industry and the agricultural economy. In various cotton fields and cultivars in Şanlıurfa during the summer of 2022, pink boll rot and stem and leaf desiccation were observed. About 5% of cotton bolls and stems were severely affected or completely desiccated, covering an area of 40 ha in the July-August. Initially, the symptoms appeared as small spots on bolls, followed by the expansion of mycelial growth that eventually covered the entire boll. When bolls were infected at early stages, they formed desiccated, closed or small cracked bolls. Under severe disease pressure with the high humidity, entire bolls became pink in color. Our observations revealed that the pathogen can infect not only the bolls but also the stems, resulting in stem blight. The symptoms resembled 'die-back' observed in woody plants. Notable is the fact that the stems of mature plants infected by the pathogen exhibited a "Bushy" appearance. However, main stems of the young plants infected by the pathogen exhibited wilting of the entire plant. When the disease initially appeared on the stems, the pathogen grew all around, continued to expand, and eventually caused complete stem desiccation and stem death. Sections of symptomatic bolls (n=24) and stems (n=15) were cut into 2- to 3-cm pieces, treated with a 2% sodium hypochlorite (NaOCl) solution for 30 s and placed on potato dextrose agar. All 15 plant parts cut from 12 different infected plants consistently developed a flat, granular, and powdery appearance with a light pink colony. The conidia (n = 6) were two-celled, thick-walled, hyaline, and ellipsoid to pyriform in shape (12 to 20 x 7 to 10 µm), forming characteristic zigzag chains. The conidiophores were upright, straight, or slightly curved; generally simple, though sometimes branched; septate. These morphological characteristics were consistent with Trichothecium roseum descriptions in Barnett and Hunter (1972). Pathogenicity tests were performed on both bolls and seedlings (30-days-old) of cotton by inoculating them with spore suspensions (105 conidia/ml within sterilized distilled water), whereas the control plants (n=3) were sprayed with water. Inoculated plants and bolls were incubated at 15-25 °C to induce disease development in a greenhouse. Fifteen days after artificial inoculation, seedlings and bolls exhibited the same symptoms that were observed in the field, and isolates morphologically identical to the original isolate were recovered from symptomatic tissues. However, the control group showed no symptoms. DNA was extracted, and the β-tubulin (TUB2) and large subunit (LSU) regions were amplified using primers Bt2a/Bt2b and LROR/LR5, respectively (Glass Rehner & Samuels 1994). The PCR products had sizes of approximately 312 bp for TUB2 and 840 bp for LSU (GenBank accession numbers OQ848674.1 and OR083418, respectively). The TUB2 and LSU sequences showed 98% and 100% similarity, respectively, to Trichothecium roseum sequences in the NCBI database (OP868701.1 and AY261181.1). This is the first report in Türkiye of T. roseum causing boll rot and stem blight in cotton. Although it has currently been found only on cotton in Şanlıurfa, its broad host range and potential impact on yield and quality make continuous monitoring essential.
Ölmez et al. (Sun,) studied this question.