Evaluation of Bio-Inoculant Effects on the Growth Performance and Establishment of Genetically Varied Citrus Rootstocks

The application of plant growth-promoting rhizobacteria (PGPR) represents a promising approach for improving citrus rootstock establishment and development. This study investigated the effects of PGPR bio-inoculants on growth parameters across eight genetically distinct citrus rootstocks. The experimental design comprised Rough lemon, Carrizo citrange, Rangpur lime, Gou Tou, Sun Chu Sha, Swingle citrumelo, Troyer citrange, and Volkameriana rootstocks. These were treated with three bio-inoculant conditions: Bacillus subtilis (10 ⁸ cfu ml ^− 1 ), Pseudomonas fluorescens (10 ⁸ cfu ml ^− 1 ), and their consortia ( B. subtilis + P. fluorescens (10 ⁸ cfu ml ^− 1 ), along with an untreated control, in a completely randomized design with three replications. Observations at 90 days after sowing (DAS) revealed significant treatment effects on multiple growth parameters. The consortia treatment demonstrated superior results across several rootstock combinations. Notable outcomes included maximum survival percentage (96.67%) in Swingle citrumelo with consortia ( B. subtilis + P. fluorescens) , and stem girth (1.83 mm) in Swingle citrumelo with consortia treatment. Rough lemon treated with consortia exhibited maximum seedling height (9.23 cm), leaf parameters (count: 8.07, fresh weight: 0.367 g, dry weight: 0.160 g), and leaf area (8.27 cm²). Rangpur lime with consortia treatment showed optimal root development characteristics, including dry root mass, secondary root formation (9.40), and root: shoot ratio (0.69). The P. fluorescens treatment with Carrizo citrange achieved maximum root length (8.72 cm). These findings demonstrate the significant potential of PGPR bio-inoculants, particularly in consortium applications, for enhancing the development and establishment of citrus rootstocks. The study provides valuable insights for sustainable citrus nursery management practices.