109(2)_str 18

ISSN 1392-3196 / e-ISSN 2335-8947
Zemdirbyste-Agriculture, vol. 109, No. 2 (2022), p. 139–148
DOI 10.13080/z-a.2022.109.018

Statistical production optimisation, Fusarium biocontrol and insecticidal activity of 2,4-diacetylphloroglucinol produced by a newly discovered moderately haloalkalitolerant Pseudomonas guariconensis VDA8



A newly discovered rhizobacterial strain, Pseudomonas guariconensis VDA8, was observed to secrete antimicrobial 2,4-diacetylphloroglucinol (DAPG). The strain is characterised by plant-growth promoting (PGP) traits of indole acetic acid, siderophore, exopolysaccharide, ammonia and lytic enzyme production, phosphate solubilisation, in addition to being salt (0.85 M) and alkali (pH 8.5) tolerant. Optimisation for maximal DAPG production was investigated using statistical tools viz. Plackett-Burman design (PBD) and central composite design (CCD). Out of 19 nutritional ingredients of Schlegel’s synthetic medium and physico-chemical factors, aeration and pH were discovered to be most influential by a 20-run PBD trial. A full factorial CCD with five levels was conducted using 13 experimental runs in modified Schlegel’s synthetic medium to reveal the aeration rate of 144 rpm and pH 8.9 as optimal conditions for DAPG production of 1.4 g L-1 at shake flask level. The 1 L volume fermentation for validation of the CCD model resulted in yield of 1.26 g L-1 to reveal that media volume and initial cell density are also crucial factors for DAPG production by P. guariconensis. Further, seed biopriming of chickpea (Cicer arietinum L.) demonstrated improved germination (93.3%) and vigour index (4.0) compared with non-primed seeds. The biocontrol activity examined in pot bioassay against phytopathogen Fusarium oxysporum recorded highest germination (95.5%), seedling vigour, and plant growth indices as compared to DAPG (30 μg ml-1) chemoprimed, proving P. guariconensis VDA8 has a combined PGP and biocontrol activity. Moreover, purified DAPG (1 mg ml-1) exhibited pest repellence and insecticidal activity against food storage pests Sitophilus oryzae and Rhyzopertha dominica adults with a mortality of 55–60% in chemoprimed rice after 72 h. Direct contact toxicity was recorded to reach 66–70% within 48 h at similar concentration.

The present study strongly advocates the use of P. guariconensis VDA8 as a dual PGP and biocontrol agent in saline and alkaline soil as well as purified DAPG as potent insecticide for post-harvest grain preservation.

Keywords: Plackett-Burman design, central composite design, Cicer arietinum, Fusarium oxysporum, Sitophilus oryzae, Rhyzopertha dominica.

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