The role and prevalence of Fusarium oxysporum f.sp. vasinfectum as a damping-off pathogen in cotton in Aydın province

Objective: This study aimed to determine the role of Fusarium oxysporum f. sp. vasinfectum, one of the agents of damping-off disease, during the seedling stage of cotton and its prevalance in the cotton growing areas on a district basis in Aydın Province. Material and method: In order to collect disease agents, diseased seedling samples showing damping-off symptoms were taken from cotton fields in Koçarlı, İncirliova, Germencik, Nazilli, Köşk and Söke districts of Aydın Province in 2022 and 2023. Isolates were recovered from the collected samples and were purified. Single spore isolations were made from the purified isolates. First of all, the isolates were identified at the genus level and among the isolates in the Fusarium genus, F. oxysporum f. sp. vasinfectum were morphologically identified. In order to verify identification, DNA isolation of the isolates was done and molecular identification was performade by PCR. In order to determine whether F. oxysporum f. sp. vasinfectum isolates were pathogenic, pathogenicity tests were conducted on the commercial cotton variety 'Fiona' with randomly selected representative isolates. Results: In 2022, 218 isolates were obtained from 36 fields in Koçarlı, İncirliova, Germencik, Nazilli, Köşk and Söke districts of Aydın province, and 322 isolates were obtained from 37 fields in 2023. Among the isolates obtained in 2022, 40 Rhizoctonia spp., 3 Aspergillus spp., 1 Macrophomina spp., 2 Alternaria spp. and 191 Fusarium spp. were identified in Aydın province; and among the isolates obtained in 2023, 71 Rhizoctonia spp., 25 Alternaria spp., 217 Fusarium spp. were identified. For the verification of the diagnosis of F. oxysporum f. sp. vasinfectum, molecular studies were conducted for 135 of 191 Fusarium spp. isolates obtained from the 2022 growing season and positive results were obtained from 111; 49 isolates were found positive among 50 which were randomly selected from 227 Fusarium spp. isolates collected from the 2023 season. Among 45 F. oxysporum f. sp. vasinfectum isolates subjected to pathogenicity, all but except one were found to be pathogenic. The disease severity values of the isolates varied between 0,00% and 100%. Conclusion: According to the results, the main pathogen causing damping-off in cotton fields of Aydın province was Fusarium spp. In addition, it was revealed that the role of F. oxysporum f. sp. vasinfectum, which is main subject of this study, in seedling death in cotton was found to be significant. According to field surveys, the mean of the seedling losses due to damping-off in cotton fields of Aydın province were 3.62%, but it varied according to districts and fields. In the pathogenicity tests, F. oxysporum f. sp. vasinfectum isolates had pathogenic characteristics on cotton variety 'Fiona'.