Effect of the NFT nutrient solution pH on root transmission of tomato bacterial canker (Clavibacter michiganensis subsp michiganensis)

Effect of pH of the NFT nutrient solution on the survival of Clavibacter michiganensis subsp. michiganensis (Cmm) and its infectivity to greenhouse tomato was investigated. In a laboratory experiment, less than 20% Cmm bacteria survived for two hours in NFT solutions with a pH of 4.0 or 4.5, while 25 and 48% survived at a pH 5.0 or 5.5. At pH 6.0 and 6.5, however, most of the bacteria survived for six hours in the solution. A NFT experiment was conducted to test the effect of pH on the population dynamics of Cmm and its infectivity to tomato, in which two pH regimes, i.e., low (5.0) and high (6.0), were compared. The bacteria were introduced into the NFT system by transplanting two infected plants into each row. During the experiment, the bacterial population was notably lower in the NFT solution with a low pH than that with a high pH. Seventy days later, eighteen of 24 plants developed the disease at high pH, while only six of the 24 plants were infected at the low pH. The pH of the solution appeared to have little effect on the fresh weight of plants. Introducing the canker bacteria into the NFT nutrient solution significantly reduced the fresh weight of plants regardless of the pH tested.