Effect of Plant Growth Promoting Rhizobacteria on the Development and Biochemical Composition of Cucumber under Different Substrate Moisture Levels

<i>Cucumis sativus</i> L. plants are subjected to stress during production, affecting their growth, development, and fruit quality due to abiotic factors. Thus, the aim of this research is to evaluate <i>Pseudomonas paralactis</i>, <i>Sinorhizobium meliloti</i>, and <i>Acinetobacter radioresistens</i> plant growth promoting rhizobacteria (PGPR) effect on <i>C. sativus</i> plants under three substrate moisture levels (100, 75, and 50%). A randomized complete block design (RCBD) was used with an A x B arrangement: (1) factor A (inoculant) with four levels; (2) PGPR and control (without bacterium); (3) factor B (substrate moisture content) with three levels. Plant height, root length, and fresh weight increased by inoculating PGPR (121%, 135%, and 134%, respectively); likewise, these variables increased with higher moisture content (177%, 204%, and 234%, respectively), while the effect of the interactions of the PGPR and the moisture content in the substrate showed statistical differences in plant height increasing of 197% and root length of 267%. On the other hand, the content of phenols, flavonoids, and antioxidant capacity was statistically different (<i>p</i> ≤ 0.05) in inoculated plants, with PGPR increasing by 117%, 126%, and 150% respectively. In the moisture content of the substrate, statistical differences were observed, with an increase in the flavonoid content (114%) and antioxidant capacity (116%). The assimilation of nitrogen was higher by 274% and phosphorus by 124% with the PGPR inoculation, the moisture content increased the nitrogen content in the plant (257%) and the phosphorus content in plant (135%), showing significant differences (<i>p</i> ≤ 0.05). However, the interaction of PGPR and moisture content only presented statistical differences in nitrogen assimilation. PGPR can be considered as an alternative to obtain vigorous cucumber seedlings.