Abstract:

This study aimed to explore the potential of the synergistic control of rubber root diseases by Bacillus subtilis and chemical fungicides, and provide a basis for the sustainable prevention and control of rubber root diseases. The efficacy of seven fungicides and Czk1 strain against rubber red root disease and rubber brown root disease and the bio-compatibility of fungicides with Czk1 were determined by the inhibition zone and plate colony counting methods, while the combined effect was determined by the Horsfall method. The half-maximal inhibitor concentration (EC₅₀) of "Gen Kang" on rubber red root disease and rubber brown root disease was 0.6253 μg/mL and 0.0522 μg/mL, respectively, which represented the lowest EC₅₀ and showed good bio-compatibility with Czk1. "Gen Kang" (EC₅₀=0.6253 μg/mL) was mixed with Czk1 (EC₅₀=6.46×10 ⁷ CFU/mL) in the volume ratio of 3∶7, respectively, against rubber red root disease and yielded I_R value of 1.60, which was higher than the I_R value of 1.51 that was obtained when "Gen Kang" (EC₅₀=0.0522 μg/mL) was mixed with bio-control bacteria Czk1 (EC₅₀=2.33×10 ⁸ CFU/mL) in the same volume ratio. The results showed that "Gen Kang" could be used in combination with B. subtilis Czk1 to control rubber root disease as demonstrated by the significantly higher inhibitory effect obtained from their combined performance than when both "Gen Kang" and B. subtilis Czk1 strain were used independently. The use of "Gen Kang" in the mixture was only one-third (1/3) of that of single agent, which greatly reduced the use of chemical agents.

Key words: rubber red root disease, rubber brown root disease, Bacillus subtilis, "Gen kang", synergistic prevention