Identification of biocontrol strain and screening of fungicides against Corynespora leaf spot on tobacco in Guizhou Province

In order to effectively control the tobacco Corynespora leaf spot, the biocontrol strain YC2140 screened in the previous work of our laboratory was identified by Biolog automatic microbial identification systemlog automatic microbial identification system 16S rRNA and gyrB sequence molecular identification. Five fungicides commonly used in production and YC2140 were selected for pot and field control experiments. Results showed that the YC2140 strain was identified as Pseudomonas fluorescens by molecular method and Biolog identification system. The pot experiment results showed that under the recommended dosage (449.78 mL/hm² or 449.78 g/hm²), the control efficacy on Corynespora leaf spot from high to low was fluazinam 500 g/L SC (the control efficacy was 78.77%), prochloraz 450 g/L EW (77.85%), tebuconazole 430 g/L SC (67.12%), 1 × 10⁸ cfu/mL YC2140 fermentation broth (61.64%) and boscalid 50% WG (46.12%). The field trial results under the same dosage showed that the control efficacy from high to low was prochloraz 450 g/L EW (43.33%), fluazinam 500 g/L SC (40.97%), tebuconazole 430 g/L SC (27.94%), 1 × 10⁸ cfu/mL YC2140 fermentation broth (26.15%), 70% mancozeb WP (dosage 2998.50 g/hm², control efficacy 21.99%). The results of this study can provide reference for the screening of fungicides for the control of tobacco Corynespora leaf spot disease.