Delving into Chemical Control Options for Bacterial Canker (Clavibacter michiganensis subsp. michiganensis) in Tomatoes: An In-vitro Study

The 2022/2023 tomato crop witnessed the emergence of Clavibacter michiganensis subsp. michiganensis in a tomato field, leading to symptoms resembling bacterial canker. Identification of the suspected bacterium, C. michiganensis subsp. michiganensis, utilized specific primers (CMM5 and CMM6) for PCR reaction, resulting in a 614 bp fragment. Several fungicides and bactericides were tested for their ability to control bacterial growth in Petri dishes. Fungicides and bactericides that completely inhibit the bacterial growth in Petri dishes included benzalkonium chloride (250 mg a.i./L), copper oxychloride (1680 mg a.i./L with 1000 mg metallic copper/L), copper hydroxide (2764 mg a.i./L with 1800 mg metallic copper/L), fluazinam (500 µL a.i./L), difenoconazole + pidiflumetofen (200 + 120 µL a.i./L), cuprous oxide (1344 mg a.i./L with 1200 mg metallic copper /L), mancozeb + famoxadone (1000 + 100 mg a.i./L), mancozeb (4000 mg a.i./L) and metiram + pyraclostrobin (2200 + 200 mg a.i./L). The packaged dose of casugamycin (60 µL a.i./L) failed to completely inhibit C. michiganensis subsp. michiganensis growth, necessitating doses exceeding 140 µL a.i./L for complete inhibition. Only at a dosage of 140 µL a.i./L was there no observable growth on the Petri dish containing YDC. Label doses of casugamycin did not prevent the growth of any bacteria, albeit partially controlling Clavibacter and Pectobacterium populations. At the dose of 140 µL a.i./L, the sole bacterium that proliferated was Xanthomonas hortorum pv. gardneri. The other bacteria were included in this study focusing on Clavibacter solely to understand the effect of certain products on other important bacteria in tomato cultivation. The active ingredients, difenoconazole + pidiflumetofen (200 + 120 µL/L active ingredient) and fluazinam (500 µL/L active ingredient) effectively suppressed C. michiganensis subsp. michiganensis growth. The study indicates that various tested fungicides and bactericides were effective in curbing C. michiganensis subsp. michiganensis growth under laboratory conditions. Nonetheless, efficacy may fluctuate based on dose and specific product used. Further research, including field trials, is imperative to evaluate product efficacy under real-world conditions and devise comprehensive management strategies for tomato bacterial canker control.