UNRAVELING THE PROTECTIVE POTENTIAL OF SPERMOSPHERE BACTERIA IN MITIGATING RICE BROWN SPOT (Bipolaris oryzae (Breda de Haan) Shoemaker) INFECTION - J. Sheela; E. G. Ebenezar; M. Theradimani; S. Ragul; M P. Tamilmalar; A. Aravinthkumar; N. Rajinimala; M. Paramasivan; M. Arumugampillai (Journal of Animal and Plant Sciences, 2024)
Bipolaris oryzae, fungal pathogen causing rice brown spot disease, exerts a significant economic impact by reducing rice yield and quality. The costs associated with the management of this destructive pathogen, including fungicide applications and other preventive measures, increase the cost of cultivation and pave the way for the economic burden faced by rice farmers and the broader agricultural industry. Taking this into consideration, 32 spermosphere bacteria were isolated from various rice landraces and challenged against the virulent isolate of Bipolaris oryzae (OM977033) under in vitro conditions. Among them, six strains of spermosphere bacteria from different rice seeds exhibited notable inhibitory effects on the tested pathogen. SPKKM 4 isolated from Navara, SPKKM 2 from Mappillaisamba, SPKKM 5 from Navara black, SPKKM 18 from Kavuni, SPKKM 9 from Mallikar and SPKKM 32 from ADT 44 rice seeds exhibited pronounced inhibition of Bipolaris oryzae mycelial growth. Furthermore, seedling vigor assessments revealed the remarkable growth-promoting potential of SPKKM 5, SPKKM 4, and SPKKM 2 among the tested bacterial strains. Molecular characterization confirmed their identities as Bacillus subtilis (OQ073461), Acinetobacter schindleri (OK342196) and Acidovorax spp. (OP522279), respectively. Subsequent pot culture experiments demonstrated that Bacillus subtilis (SPKKM 5) applied at 10 ml kg-1 as seed treatment and foliar spray (0.5%) at flowering and 15 days later, resulted in a remarkable 65.86% reduction in disease incidence compared to the control.
Keywords: journal article; Rice brown spot; Bipolaris oryzae; spermosphere bacteria; rice landraces; Bacillus subtilis