Plant growth-promoting endophytic bacteria enhance cucumber growth and yield in a two-year field trial

Plant growth-promoting (PGP) endophytic bacteria are known to benefit plant growth and crop yields in controlled environment experiments, but their efficacy under open-field conditions and over multiple seasons has rarely been validated. Here, we conducted a two-year (2018-2019) open-field trial in a randomized block design to test five individual endophytic bacterial strains (Strain 4 = Curtobacterium sp., Strain 72 = Brevibacillus sp., Strain 167 = Paenibacillus sp., Strain 193 = Bacillus sp., Strain 227 = Microbacterium sp.) applied as cucumber seed inoculants, with an uninoculated control. All five strains enhanced at least one growth or yield component, while strains 4 and 227 consistently produced significantly higher total fruit weight per plant than the uninoculated control in both years (p < 0.05, Tukey's HSD). Fruit number and average fruit weight were also improved in a strain- and year-dependent manner. This study represents the first two-season field validation of single-strain endophytic inoculants in cucumber. These results demonstrate consistent growth and yield benefits from endophytic bacteria and highlight their promise as sustainable biofertilizers for cucumber production under field conditions.