Early Seedling Growth Responses to Gluconacetobacter diazotrophicus Inoculation in Sugarcane: A Multivariate and Semi-Mechanistic Analysis

Gluconacetobacter diazotrophicus is a sugarcane-associated diazotrophic endophyte whose functional relevance includes carbon oxidation, auxin-related signaling, colonization, and persistence. This study evaluated early sugarcane seedling responses to G. diazotrophicus inoculation under greenhouse conditions using phenotypic, multivariate, and semi-mechanistic analyses. The inoculum was supported by culture recovery, preservation continuity, and PCR-based molecular evidence, while seedling performance was assessed across eight treatments using shoot length, root length, net gains, total biomass, and root-to-shoot allocation. Responses were treatment-dependent rather than uniformly growth-promoting. The non-inoculated water control T8 reached the highest absolute endpoint performance, whereas T2 was the strongest inoculated treatment, showing the most balanced profile across shoot gain, root gain, and total biomass. Treatment contrasts separated absolute control performance from inoculated-treatment ranking. Multivariate profiling confirmed strong treatment separation (PERMANOVA: pseudo-F = 114.07, R2 = 0.700, p = 0.001), and the standardized fingerprint showed that greater inoculum complexity did not necessarily translate into stronger plant response. The semi-mechanistic model explained 72.8% of total biomass variation, with acceptable collinearity (maximum VIF = 2.77). Overall, early seedling performance was structured by exposure, inoculum architecture, and phenotypic expression rather than inoculation presence alone.