Beneficial bacterial endophytes promote spinach plant growth under indoor vertical hydroponics

Hydroponic and vertical farming technologies have grown rapidly in recent years as there are many advantages including year-round production, short growth cycles, greater efficiency of water and nutrient use, prevention of soil-borne diseases and insects, longer shelf life, etc. Spinach (<i>Spinacia oleracea</i>) is a popular leafy green and a good source of vitamins and minerals. Although methods of spinach production in hydroponic systems have been improved including lighting, fertilizer solutions, and others, plant growth could be further promoted to increase profitability and compensate for initial startup costs. One way to increase spinach yields is to use plant growth-promoting bacteria, which can promote plant growth, enhance nutrient uptake, increase stress tolerance as well as inhibit pathogen growth. Two bacteria (<i>Pseudomonas psychrotolerans</i> IALR632 and <i>Enterobacter asburiae</i> IALR1379) were tested with two spinach cultivars ('Red Snapper' and 'Seaside') using indoor vertical nutrient film technique systems. Inoculations of IALR632 and IALR1379 significantly increased the shoot fresh weight of 'Red Snapper' by 19.3% and 13.3%, and that of 'Seaside' by 17.8% and 14.1% at harvest, compared with their control treatments, respectively. Both bacterial inoculations enhanced root growth of 'Red Snapper', but not 'Seaside'. Additionally, inoculation of IALR632 significantly increased leaf greenness of both 'Red Snapper' and 'Seaside', but IALR1379 did not. Both bacterial endophytes colonized the inside of the roots and translocated to shoots of 'Red Snapper' and 'Seaside'. Overall, IALR632 is more effective at increasing spinach yields, root growth, and leaf greenness compared to IALR1379 under indoor vertical hydroponic systems.