Brevibacillus formosus strain NJTU05 powder formulation bioproduct to control root and stem rot disease of durian

Abstract

The beneficial bacterium Brevibacillus formosus strain NJTU05 has demonstrated high efficacy in controlling Phytophthora palmivora, the causal agent of root and stem rot in durian, as well as other significant fungal diseases, such as damping-off (Pythium sp.) and branch wilt (Fusarium sp.). This study aimed to develop a water-soluble powder bio-product containing B. formosus NJTU05 as the active agent for convenient use by farmers. Three formulations were prepared using bacterial cell sediment of NJTU05 mixed with various nutrients and carriers. Formulation 1 (JF-1) consisted of bacterial sediment (1 × 10¹⁵CFU/ml): pre-gelatinized starch: corn starch: sucrose in a ratio of 10:15:60:15. Formulation 2 (JF-2) included bacterial sediment (1 × 10¹⁵CFU/ml): pre-gelatinized starch: corn starch: tapioca starch: sucrose in a ratio of 10:15:30:30:15, while Formulation 3 (JF-3) consisted of bacterial sediment (1 × 10¹⁵ CFU/ml): pre-gelatinized starch: tapioca starch: sucrose in a ratio of 10:15:60:15. Among the three, JF-1 exhibited the best physical and biological properties, showing good solubility, stability in water, and superior viability, retaining 1.8 × 10¹² CFU/ml after six months of storage compared to 0.5 × 10⁶ CFU/ml and 0.3 × 10⁶ CFU/ml for JF-2 and JF-3, respectively. Laboratory and greenhouse testing confirmed JF-1’s effectiveness in inhibiting P. palmivora strain P-TU12 mycelial growth with a 77.96% inhibition rate, comparable to fresh NJTU05 cultures grown on standard NGB medium (76.48%) and significantly higher than the commercial bioproduct Bacillus subtilis (14.26%, p ≤ 0.05). Field trials in Tha Mai District, Chanthaburi, demonstrated that soil application and foliar spray of JF-1 reduced disease severity by 80.56% when applied at 100 liters/tree every 7 days for four applications. This efficacy was comparable to fresh bacterial cultures (78.67%) and superior to commercial products (68.22%, p ≤ 0.05). JF-1 proved to be a highly effective, user-friendly solution for fungal disease control in durian cultivation.