Paenibacillus polymyxa reduces leaf spot disease caused by Cersocpora sp. and has potential to promote growth in green oak lettuce (Lactuca sativa var. crispa) in the commercial hydroponic farm

Cercospora sp. caused leaf spot disease in green oak lettuce (Lactuca sativa var. crispa) grown hydroponically in Phetchaburi, Prachuap Khiri Khan and Rayong, Thailand. Paenibacillus polymyxa (isolate 4), which was also reported to inhibit the mycelial growth of Pythium helicoides, was effective in inhibiting the mycelial growth of Cercospora sp. on potato dextrose agar (PDA). The simple culture of Paenibacillus polymyxa (isolate 4) was prepared and tested with green oak lettuce grown in the nutrient film technique (NFT) in the commercial farm. The bacterial culture not only reduced the severity of leaf spot disease caused by Cercospora sp., but also statistically increased dry weight of root when the bacterium was applied at 1:100 proportion (v/v, bacterial culture/nutrient solution). The application of this bacterium also potentially impacts positively the fresh weight of shoot and root, as well as the dry weight of shoot.