A Sustainable Biostimulant Strategy for Producing Vigorous Black Pepper Seedlings: Combining Plant Growth-Promoting Rhizobacteria (PGPR) and Seaweed Extract

High Resolution Image Download MS PowerPoint Slide Black pepper ( Piper nigrum L. ) requires vigorous seedlings for reliable field establishment. We evaluated whether inoculation with Azospirillum brasilense (AbV5), Bacillus subtilis (BV09), or Trichoderma asperellum (BV10), alone or in consortium, combined with Ascophyllum nodosum extract, improves seedling performance. A randomized block trial used a 2 × 4 factorial (seaweed: yes/no × inoculant) plus five controls (total 13 treatments). Plant height, shoot and root dry mass, and leaf macro- and micronutrients were measured at 120 days. Significant interactions occurred for height and root biomass. A. brasilense with seaweed achieved the greatest height (28.08 cm) and root mass (1.06 g), whereas B. subtilis alone maximized shoot mass (13.67 g). Seaweed increased foliar P (+49%), K (+55% with B. subtilis ), Fe (+63.5% with A. brasilense ) and B (+125.1% in the consortium). The consortium under seaweed underperformed for some traits, suggesting antagonism. Targeted single inoculants, especially A. brasilense or B. subtilis, combined with A. nodosum extract, are a promising, sustainable approach to produce more vigorous, nutritionally balanced seedlings.