Assessing the allelopathic effect of Chrysopogon zizanioides (L.) Roberty root methanolic extract on Brassica rapa var. parachinensis using an untargeted metabolomic approach

Muhd Arif Shaffiq Sahrir1, Nornasuha Yusoff1*, Kamalrul Azlan Azizan2, and Nor Atirah Mohd Aridi1
Chrysopogon zizanioides (L.) Roberty, or vetiver grass, is a deep-rooted perennial grass. An examination of allelopathy using a metabolomic approach offers valuable insights into vetiver extract’s mechanism of action and phytotoxicity. This study utilised an untargeted metabolomics approach through the use of choisum (Brassica rapa L. subsp. chinensis (L.) Hanelt var. parachinensis (L.H. Bailey) Hanelt) as target plant because it is easier to cultivate and susceptible to the extract. Vetiver root methanolic extracts at various concentrations (0, 0.1, 1, 10, 50, and 100 mg mL-1) were sprayed at 100 mL m-2 on choisum seedlings at the 2 to 3 leaves stage. After 21 d, the Soil Plant Analysis Development (SPAD) and chlorophyll content of exposed choisum were measured, and their metabolites were subjected to gas chromatography-mass spectrometer (GC-MS)-based metabolomics analysis. The result demonstrated that the 100 mg mL-1 methanolic extract significantly decreased SPAD reading by 57.29% and reduced chlorophyll content by 66.38% (chl a) and 73.49% (chl b) of choisum compared to the control. Furthermore, considerably reduced stomatal length of exposed choisum, up to 34.31%, was observed when exposed to maximum concentration (100 mg mL-1). In total, nine metabolites with variable importance in projection (VIP) > 1 and P < 0.05 were found and identified as amino acids and carbohydrates. The highest concentration of extract enriched pathways of propanoate, Se-compound, cysteine, and methionine metabolism in choisum, suggesting the extract induced plant stress. The findings confirm the allelopathic potential of vetiver root and provide insight into the response of choisum to the allelopathic activity of vetiver grass root methanolic extract.
Keywords: Allelopathy, Brassica rapa, Chrysopogon zizanioides, metabolomics, vetiver grass.
1Universiti Sultan Zainal Abidin, Faculty of Bioresources and Food Industry, School of Agriculture Science and Biotechnology, 22200 Besut, Terengganu, Malaysia.
2Universiti Kebangsaan Malaysia (UKM), Institute of Systems Biology (INBIOSIS), 43600 UKM Bangi, Selangor, Malaysia.
*Corresponding author (nornasuhayusoff@unisza.edu.my).