Volatile organic compounds emitted by the biocontrol agent Pythium oligandrum contribute to ginger plant growth and disease resistance
The oomycete Pythium oligandrum is a potential biocontrol agent to control a wide range of fungal and oomycetes-caused diseases such as Pythium myriotylum-caused rhizome rot in ginger leading to reduced yields and compromised quality. Previously, P. oligandrum has been studied for its plant growth-promoting potential by auxin production and induction of disease resistance by elicitors such as oligandrin. Volatile organic compounds (VOCs) play beneficial roles in sustainable agriculture by enhancing plant growth and resistance. We investigated the contribution of P. oligandrum-produced VOCs on plant growth and disease suppression by initially using N. benthamiana plants for screening. P. oligandrum VOCs significantly enhanced tobacco seedling and plant biomass content. Screening of the individual VOCs showed that 3-octanone and hexadecane promoted the growth of tobacco seedlings. The total VOCs from P. oligandrum also enhanced the shoot and root growth of ginger plants. Transcriptomic analysis showed a higher expression of genes related to plant growth hormones, and stress responses in the leaves of ginger plants exposed to P. oligandrum VOCs. The concentrations of plant growth hormones such as auxin, zeatin, and gibberellic acid were higher in the leaves of ginger plants exposed to P. oligandrum VOCs. In a ginger disease biocontrol assay, the VOC-exposed ginger plants infected with P. myriotylum had lower levels of disease severity. We conclude that this study contributes to understanding the growth-promoting mechanisms of P. oligandrum on ginger and tobacco, priming of ginger plants against various stress and the mechanisms of action of P. oligandrum as a biocontrol agent. Overall design: Transcriptome analysis was performed on leaf blades from three ginger (Zingiber officinale) plants exposed to volatile compounds from Pythium oligandrum for 21 days using a plastic pot-glass jar apparatus whereby P. oligandrum was grown in the glass-jar and ginger was grown in the plastic pot placed on top of the glass jar. For the control, leaf blades were sampled from three ginger plants that were not exposed to P. oligandrum volatile compounds using the same plastic pot-glass jar apparatus whereby nothing was grown in the glass-jar and ginger was grown in the plastic pot placed on top of the glass jar.