Biopriming Pseudomonas fluorescens to vegetable seeds with biopolymers to promote coating efficacy, seed germination and disease suppression

Abstract

• Xanthan gum (0.2% w:v) is most compatible with P. fluorescens and seeds. • Coating improves the viability of bioagent on seed surface. • SEM micrographs show distribution of P. fluorescens on seed by xanthan gum. • Biopriming with P. fluorescens promoted radicle growth of pak choy seedlings. • Biopriming chilli seeds with P. fluorescens suppressed disease by P. ultimum. In this study, biopolymers (sodium alginate, carboxymethylcellulose, gum arabic, xanthan gum) were used to bioprime the biocontrol agent (BCA) Pseudomonas fluorescens to pak choy ( Brassica rapa ) and chilli ( Capsicum annum ) seeds. The compatibility of the biopolymers with seeds and BCA was assessed by evaluating the survival of BCA, the percentage of BCA entrapped, and the influence of bacterial concentration on seed germination. The optimal condition was then selected for seed biopriming and disease tolerance studies. Results revealed that all biopolymers were compatible with P. fluorescens with the most effective biopolymer identified as 0.2% w:v xanthan gum (XG0.2). XG0.2 coated 70.48% and 69.91% of viable bioagent on pak choy and chilli seeds, respectively, and retained viability of P. fluorescens (4.33 – 4.64 Log CFU/seed) 24 h post biopriming. The most effective bacterial concentration for biopriming pak choy and chilli seeds were recorded as 10 7 and 10 2 bacterial cells/mL, respectively. The pot trial revealed that the bioprimed chilli seeds performed better against Pythium ultimum as lower disease severity (DS, 4.00 ± 2.19%) and better physiological attributes were recorded. On the contrary, P. fluorescens was less effective in suppressing disease in pak choy compared to chillies. The disease suppresion of Fusarium solani by P. fluorescens was not observed in potted trial. To conclude, our study showed the importance of xanthan gum as an effective coating matrix to coat P. fluorescens on seeds and their potential in promoting seedling growth and suppressing disease infection.