Effects of a microbial treatment of Lactobacillus casei, Saccharomyces cerevisiae, and Lactobacillus plantarum on blueberry fruit quality, rhizosphere soil properties, and bacterial communities.

INTRODUCTION: Microbial amendments are increasingly used in sustainable crop production, but it remains unclear whether their application is accompanied by coordinated changes in fruit traits, rhizosphere soil conditions, and resident bacterial communities in blueberry cultivation. This study examined whether microbial culture treatment was associated with concurrent changes in blueberry fruit performance, rhizosphere soil chemical properties, and bacterial community characteristics.

METHODS: Highbush blueberry (Vaccinium corymbosum L. cv. Duke) plants receiving no microbial treatment (NT) were compared with plants receiving a microbial culture treatment (BT) consisting of Lactobacillus casei, Saccharomyces cerevisiae, and Lactobacillus plantarum through drip irrigation. Fruit set date and soluble solids content were evaluated together with harvest-time rhizosphere soil chemical properties, bacterial community characteristics based on full-length 16S rRNA gene sequencing, and exploratory predicted bacterial functional potential.

RESULTS: Relative to NT, BT showed first visible fruit set 10.89 days earlier and higher soluble solids content, increasing from 11.33 ± 1.00 to 15.00 ± 0.71 °Brix. BT was associated with lower electrical conductivity, cation exchange capacity, total nitrogen, ammonium nitrogen, exchangeable K, Ca, Mg, and organic matter, whereas available phosphorus was higher. Soil pH, exchangeable Na, salinity, and nitrate nitrogen did not differ significantly between treatments. Bray-Curtis analysis suggested treatment-associated clustering of bacterial communities; however, PERMANOVA did not detect a statistically significant difference in overall community composition (pseudo-F = 1.464, R 2 = 0.268, p = 0.100). Within the treatment-responsive bacterial sequence-feature subset, BT showed greater observed richness and diversity, and exploratory taxonomic and predicted MetaCyc pathway analyses identified treatment-associated patterns.

DISCUSSION: Microbial culture treatment was associated with coordinated differences in blueberry fruit traits, rhizosphere nutrient conditions, and bacterial community characteristics. However, the present design does not establish causal relationships among these responses. Because the cultures were applied in growth media without a separate sterile medium control, the effects of viable microorganisms could not be distinguished from potential effects of medium-derived components.