Co-cultivation of Bacillus amyloliquefaciens and Trichoderma harzianum: Synergistic effects on plant growth and biocontrol of jasmine collar rot

Jasmine (Jasminum officinale) is a valuable and culturally significant flowering crop in India. Still, its cultivation is greatly impacted by collar rot disease, caused by Sclerotium rolfsii Sacc., resulting in yield losses of up to 50%. This study explores co-culture technology, utilizing Trichoderma harzianum TR(D)-4 and Bacillus amyloliquefaciens BC(M)-2, as an integrated single-product solution for the biological control of this pathogen. Field surveys conducted across major jasmine-growing districts in Tamil Nadu revealed a range of disease severity (20% - 52%) and incidence (29% - 64%). The collar rot pathogen, and biocontrol agents were isolated from surveyed locations and identified through morphological characteristics and molecular phylogenetic analysis based on ITS and 16S rDNA sequences. In vitro assays using dual-plate and paired-plate methods demonstrated that Bacillus amyloliquefaciens BC(M)-2 achieved inhibition rates of 71.34% and 78.27%, respectively, while Trichoderma harzianum TR(D)-4 exhibited inhibition rates of 86.27% and 75.43% against Sclerotium rolfsii SR(D)-5. Co-culturing these antagonistic strains synergistically improved antifungal effectiveness, achieving an 87% inhibition rate against S. rolfsii compared to their separate cultures. The synergistic interaction in co-culture promoted the production of novel compounds, including alpha-bisabolol (AB), bis(2-ethylhexyl) phthalate, and harziandione, which enhanced plant growth and inhibited S. rolfsii. Further planta studies confirmed that the co-culture significantly reduced disease incidence and enhanced plant growth in both pre-and post-inoculation strategies. This research highlights the potential of co-culturing T. harzianum TR(D)-4 and B. amyloliquefaciens BC(M)-2 as an effective and sustainable approach for managing collar rot disease in jasmine.