Endophytic bacillus consortium formulation for plant growth promotion and management of chilli anthracnose

Abstract

The present study entitled “Endophytic Bacillus consortium formulation for plant growth promotion and management of chilli anthracnose” was carried out at the College of Agriculture, Vellayani (2022–2024) to develop and evaluate effective formulations of endophytic Bacillus consortium for improving plant growth and managing anthracnose disease in chilli (Capsicum annuum L.). Thirteen compatible endophytic Bacillus isolates, obtained through previous studies conducted at the Department of Plant Pathology were assessed for their antagonistic activity against Colletotrichum capsici, the causal agent of chilli anthracnose. Among the isolates tested, CFLE3, WR2, WL2, and WR1 displayed strong antagonistic activity in both dual culture and culture filtrate assays. The roll towel method employed to evaluate seed germination and seedling vigour indicated that biopriming with CFLE3, WR1, WR2, and WL2 significantly improved seed germination rates, seedling growth, and biomass accumulation, while treatments with PNRE5, GR2, and NAT001 performed poorly and were comparable to the untreated control in all growth parameters. Based on their dual efficacy in antagonism and plant growth promotion, ten promising isolates viz., PNRE4, PNSE5, AR2, GR1, WR1, WR2, WL2, CBSE5, CBRE5, and CFLE3, were combined to formulate a microbial consortium. This consortium was developed into both solid and liquid bioformulations using talc, plain nutrient broth (NB), and nutrient broth amended with additives such as 2% glycerol (NB-GLY), 2% polyvinylpyrrolidone (NB-PVP), and 15 mM trehalose (NB-TREH). The population dynamics of the endophytic Bacillus consortium in different formulations were monitored over six months. While initial populations were comparable across treatments, NB-GLY maintained the highest bacterial counts throughout the storage period, followed by NB-TREH. In contrast, talc and unamended NB showed marked population decline. The in vitro efficacy of the formulations was assessed over six months using detached leaf and fruit assays, as 124

well as pro tray studies. Over the six-month evaluation period, the NB-TREH and NB-GLY formulations consistently demonstrated effective suppression of lesion progression in both detached chilli leaves and fruits artificially inoculated with Colletotrichum capsici. Seed priming with NB-TREH and NB-GLY also led to consistent improvements in all seedling growth parameters, including faster germination, higher germination percentages, increased shoot and root lengths, and enhanced fresh and dry biomass. Based on their superior performance, NB-TREH and NB-GLY were selected for in vivo evaluation of formulation of endophytic Bacillus consortium for promoting plant growth and managing anthracnose in chilli. In pot culture studies, the liquid Bacillus formulations NB-GLY and NB-TREH consistently suppressed anthracnose in chilli leaves, showing significantly reduced lesion progression (0.26–2.23 cm) and disease severity (18.12–65.62) compared to untreated and singly amended treatments. Similarly, in fruit assays, NB-GLY and NB-TREH effectively limited lesion development from 0.47 to 2.76 cm and maintained lower fruit rot severity (20.20–72.70) across all observation periods. These two bioformulations performed on par with or better than the chemical fungicide, while glycerol, trehalose alone, and the inoculated control showed poor disease suppression and complete tissue rotting by 10–15 DAI. Subsequent pot culture experiment for plant growth promotion, validated these findings, showing significant enhancement in plant growth and yield with NB-GLY and NBTREH formulations. NB-GLY-treated plants attained the greatest height (46.60 cm), earliest flowering (30.80 days), and longest shoots and roots (49.78 cm and 26.25 cm). Biomass accumulation was also highest in NB-GLY, with shoot and root fresh weights of 49.63 g and 21.28 g, and dry weights of 13.30 g and 5.70 g, respectively. Yield data further reinforced the superior performance of these formulations, with NB-TREH and NB-GLY yielding the highest fruit numbers (24.49 and 23.00) and fruit yield per plant (290.57 g and 294.98 g). Endophytic re-isolation from harvested chilli seeds confirmed the persistence of the endophytic Bacillus, with NB-GLY supporting the highest Bacillus population (1.14 × 10⁷ cfu g⁻¹), indicating successful colonization and 125

long-term survival of the inoculated bacteria. In conclusion, liquid formulation of endophytic Bacillus consortium amended with 2 % glycerol (NB-GLY) proved to be effective, eco-friendly alternatives to chemical fungicides by supporting microbial viability, suppressing anthracnose, promoting growth, and enhancing yield in chilli.