Effects of Substrate and Halotolerant Plant Growth-Promoting Bacteria on Seedling Emergence and Early Growth of Agave marmorata Roezl

Agave marmorata Roezl is a valuable species widely used for mezcal production. This study evaluated the effects of two substrates and three consortia of halotolerant plant growth-promoting bacteria (PGPB) on seedling emergence and early growth of A. marmorata. A completely randomized 2 × 4 factorial design was used. The number of emerged seedlings (NES), emergence speed index (ESI), and several morphometric and biomass traits were evaluated. Cosmopeat® significantly increased both NES and ESI compared with soil. Although PGPB inoculation did not significantly affect seedling emergence, it enhanced several growth and biomass traits. The Bacillus sp. + Stutzerimonas sp. and Priestia sp. + Streptomyces sp. consortia produced the greatest increases in stem diameter and biomass. In addition, Priestia sp. + Streptomyces sp. increased plant height, whereas Bacillus sp. + Stutzerimonas sp. increased the number of unfolded leaves. Significant substrate × inoculant interactions were detected for leaf fresh weight, root fresh weight, total fresh biomass, leaf dry weight, and total dry biomass. PCA further revealed distinct multivariate patterns among substrate × inoculant combinations, with individual treatments associated with different components of seedling growth and biomass allocation. Overall, these findings indicate that substrate selection and halotolerant PGPB inoculation can play complementary roles in improving the early establishment and growth of A. marmorata seedlings.