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. 2023 Feb 2;11(2):376.
doi: 10.3390/microorganisms11020376.

A Potential Application of Pseudomonas psychrotolerans IALR632 for Lettuce Growth Promotion in Hydroponics

Chuansheng Mei  1 , Dongfang Zhou  2 , Robert L Chretien  1 , Amy Turner  1 , Guichuan Hou  3 , Michael R Evans  2 , Scott Lowman  1
Affiliations

A Potential Application of Pseudomonas psychrotolerans IALR632 for Lettuce Growth Promotion in Hydroponics

Chuansheng Mei et al. Microorganisms. .

Abstract

Controlled environment agriculture hydroponic systems grow plants year-round without restriction from outside environmental conditions. In order to further improve crop yield, plant growth-promoting bacteria were tested on hydroponically grown lettuce (Lactuca sativa) plants. From our bacterial endophyte library, we found one bacterium, Pseudomonas psychrotolerans IALR632, that is promising in promoting lettuce growth in multiple hydroponic systems. When Green Oakleaf lettuce seeds were inoculated with IALR632 during germination, IALR632 significantly increased lateral root development by 164%. When germinated seedlings were inoculated with IALR632 and then transplanted to different hydroponic systems, shoot and root fresh weights of Green Oakleaf increased by 55.3% and 17.2% in a nutrient film technique (NFT) system in the greenhouse, 13.5% and 13.8% in an indoor vertical NFT system, and 15.3% and 13.6% in a deep water cultivation (DWC) system, respectively. IALR632 also significantly increased shoot fresh weights of Rex by 33.9%, Red Oakleaf by 21.0%, Red Sweet Crisp by 15.2%, and Nancy by 29.9%, as well as Red Rosie by 8.6% (no significant difference). Inoculation of IALR632-GFP and subsequent analysis by confocal microscopy demonstrated the endophytic nature and translocation from roots to shoots. The results indicate that P. psychrotolerans IALR632 has a potential application in hydroponically grown lettuce plants.

Keywords: Green Oakleaf; Lactuca sativa; bacterial endophytes; nutrient film technique; plant growth-promoting bacteria (PGPB).

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Effect of IALR632 inoculation on seedling growth and lateral root development. *** on the column means statistically significant difference at p < 0.001.
Figure 2
Figure 2
Effects of IALR632 inoculation on Green Oakleaf plant growth in greenhouse NFTs (12 April 2021 to 4 May 2021). *, **, *** on the columns mean statistically significant difference at p < 0.05, 0.01 and 0.001, respectively.
Figure 3
Figure 3
Effects of IALR632 inoculation on Green Oakleaf lettuce growth rates and SPAD for 4 weeks (23 September 2021 to 21 October 2021). * on the column means statistically significant difference at p < 0.05.
Figure 4
Figure 4
Effects of IALR632 on shoot (A) and root (B) growth of 5 cultivars in greenhouse NFT system (12 April 2021 to 4 May 2021). *, ** on the column mean statistically significant difference at p < 0.05 and 0.01, respectively.
Figure 5
Figure 5
Effects of IALR632 inoculation on plant growth in indoor vertical NFTs (31 March 2002 to 22 April 2022). *, ** on the column mean statistically significant difference at p < 0.05 and 0.01, respectively.
Figure 6
Figure 6
Effects of IALR632 inoculation on growth of Green Oakleaf lettuce in DWC hydroponic system in greenhouse (26 January 2022 to 16 February 2022). * on the column means statistically significant difference at p < 0.05.
Figure 7
Figure 7
Colonization and translocation of IALR632-GFP in lettuce plants. (A) Confocal image from the control root with 10× magnification. (B) A confocal image of the root inoculated with IALR632-GFP showing green fluorescence with 10× magnification. (C) The same root shown in B with 40× magnification showing fluorescent bacteria (arrows). (D) Colonies of IALR632-GFP reisolated from leaves of seedlings inoculated with IALR632-GFP bacteria on plates under fluorescence microscope Olympus SZX12.
See this image and copyright information in PMC

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