ASHS 2024 Conference

Controlled environment agriculture will play an important role in feeding the increasing world population as urbanization is expanding, and arable land is decreasing. Higher yields will help offset the initial high cost for building hydroponic production facilities. Beneficial bacterial endophytes have been receiving more attention in sustainable agriculture practices because they can promote plant growth, enhance nutrient uptake, and inhibit pathogen growth. The Institute for Advanced Learning and Research has established a bacterial endophyte library of more than 2000 strains and found that some bacterial endophytes significantly increased the growth of tall fescue KY31 in vitro, up to 8-fold compared with untreated control plants. In previous paper, we reported that Pseudomonas psychrotolerans IALR632 significantly promote lettuce growth in hydroponic systems. In this study, we investigated the molecular and microbiological mechanisms these bacteria exhibit for plant growth promotion in hydroponic systems through plant gene expression with RNAseq and root bacterial community changes through microbiome analysis after bacterial inoculation. Lettuce (Lactuca sativa) cultivar ‘Green Oakleaf’ was inoculated with Pseudomonas psychrotolerans IALR632 one week after seeds were sown and transplanted to nutrient film technique (NFT) hydroponic units one week after bacterial inoculation. Samples were taken at 4, 10, and 15 days after lettuce seedlings were transplanted for gene expression analysis. Root samples were taken 15 days after transplantation for microbiome analysis. Anosim, NMDS, and PCoA analyses indicated bacterial community changes in inoculated plants. The top genus relative abundance was unclassified bacteria with 87% in IALR632 treatment and 85% in control (p=0.0136). In the next top 24 genus’s relative abundance, IALR632 inoculation dramatically increased Sediminibacterium, Hyphomicrobium, Sphingobium, Devosia, Mycobacterium, Rhodoplanes, and Runella by 68%, 114%, 72%, 158%, 513%, 103% and 1920%, respectively, and reduced Methylotenera, Rhizobium, and Sphingomonas by 68%, 62% and 45%, respectively. RNAseq data showed that there were 135, 2059, and 9319 DEG between the control and bacterial treatment at 4, 10, and 15 days, respectively. These DEG are being analyzed for pathways involved in plant growth promotion.