Early seed priming by closely related Bacillus strains drives distinct metabolic and defense programs in melon

Here, we investigate how Cucumis melo responds to early seed priming with two phylogenetically related Bacillus strains: B. subtilis NCIB3610 and B. velezensis FZB42. Despite exhibiting similar colonization patterns and persistence in the root system, these strains elicit distinct, strain-specific plant responses at the developmental, metabolic, and defensive levels.

B. subtilis enhances radicle elongation and drought resilience through increased starch and L-tryptophan accumulation, while B. velezensis transiently represses early growth and reprograms host transcriptome and metabolome, including jasmonate-associated gene expression and flavonoid biosynthesis. Both treatments ultimately converge on improved performance in the phyllosphere, including enhanced resistance to Botrytis cinerea and a population of Tetranychus urticae, though via divergent physiological routes.