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 oomycete-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 Nicotiana benthamiana plants for screening. P. oligandrum VOCs significantly enhanced tobacco seedling and plant biomass contents. 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 stresses, and the mechanisms of action of P. oligandrum as a biocontrol agent. IMPORTANCE Plant growth promotion plays a vital role in enhancing production of agricultural crops, and Pythium oligandrum is known for its plant growth-promoting potential through production of auxins and induction of resistance by elicitors. This study highlights the significance of P. oligandrum-produced VOCs in plant growth promotion and disease resistance. Transcriptomic analyses of leaves of ginger plants exposed to P. oligandrum VOCs revealed the upregulation of genes involved in plant growth hormone signaling and stress responses. Moreover, the concentration of growth hormones significantly increased in P. oligandrum VOC-exposed ginger plants. Additionally, the disease severity was reduced in P. myriotylum-infected ginger plants exposed to P. oligandrum VOCs. In ginger, P. myriotylum-caused rhizome rot disease results in severe losses, and biocontrol has a role as part of an integrated pest management strategy for rhizome rot disease. Overall, growth enhancement and disease reduction in plants exposed to P. oligandrum-produced VOCs contribute to its role as a biocontrol agent.

Identification and characterization of two phospholipid hydroperoxide glutathione peroxidase genes from the Mediterranean species of the whitefly Bemisia tabaci complex.

Phospholipid hydroperoxide glutathione peroxidases (PHGPXs) are essential enzymes of the cellular antioxidant defense system during insect-plant interactions. However, little attention has been devoted to the functional characterization of PHGXPs in the whitefly Bemisia tabaci. Here, we report the identification and characterization of two PHGPX genes, designated as BtQ-PHGPX1 and BtQ-PHGPX2 from the Mediterranean species of the B. tabaci complex. Sequence analysis indicated that the length of BtQ-PHGPX1 is of 942 bp with a 729 bp open-reading frame (ORF) encoding 242 amino acids, and BtQ-PHGPX2 is of 699 bp with a 567 bp ORF encoding 188 amino acids. Sequence alignment analysis showed that BtQ-PHGPX1 and BtQ-PHGPX2 shared high similarity with other known PHGPXs. The NVASXCGXT, FPCNQFXXQEPG, and IKWNFXKFLV surrounded the reactive cysteine, glutamine, and tryptophan residues, respectively. Recombinant BtQ-PHGPX1 and BtQ-PHGPX2 were overexpressed in Escherichia coli and purified. quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis with whiteflies of different development stages showed that the mRNA levels of BtQ-PHGPX2 were significantly higher in larvae than in other stages. The mRNA levels of BtQ-PHGPX2 were significantly higher than BtQ-PHGPX1 during all the developmental stages. The mRNA levels of BtQ-PHGPX1 and BtQ-PHGPX2 in female adults were relatively higher than in male adults. The expression of BtQ-PHGPX1 and BtQ-PHGPX2 was induced by the insecticide imidacloprid. These results suggest that BtQ-PHGPX1 and BtQ-PHGPX2 may participate in detoxification of oxidative hazards in B. tabaci.