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

Cucumis sativus 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 Pseudomonas paralactis, Sinorhizobium meliloti, and Acinetobacter radioresistens plant growth promoting rhizobacteria (PGPR) effect on C. sativus 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 (p ≤ 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 (p ≤ 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.