# Elicitation of the Allelopathic Potential of Rice by Methyl Salicylate Treatment
## 3 Results and Discussion
### Phenolic Acids
The root extracts of UPR-2962-6-2-1 reported an increment of 1.6-, 1.8-, 1.6-, 1.5-, 1.5-, 1.6-, 8.2-, and 1.6-fold in the levels of all eight considered compounds, respectively (Figure 2a). The concentrations of S, V, PHB, PC, PRO, HQ, and GAL increased by 1.4-, 1.6-, 1.5-, 1.3-, 1.7-, 1.6-, and 1.5-fold in Govind roots, respectively (Figure 2b). An increase in phenolic acids also occurred in the non-competitive genotype UPR-2992-17-3-1 (Figure 1c). Though PC reached the highest levels of concentration in the shoots after all three MeSA treatments, HQ and GAL recorded the greatest differences compared to the control with values up to 2- and 2.2-fold higher at 2-mM MeSA, respectively (Figure 1c). A similar effect was detected on the phenolic content of the root extracts characterized by S, V, PHB, PC, HQ, and GAL compounds. Their concentrations reported an increase of 1.9-, 1.4-, 2.4-, 1.6-, 2.3-, and 2.1-fold, respectively (Figure 2c). \begin{table}
\begin{tabular}{c c} \hline \hline
**Phenolic Acid** & **Retention Time (min)** \\ \hline Syringic acid (S) & 9.9 \\ Vanillic acid (V) & 7.1 \\ \(p\)-Hydroxybenzoic acid (PHB) & 9.4 \\ \(p\)-Coumaric acid (PC) & 13.0 \\ Caffeic acid (CAF) & 11.6 \\ Protocatechuric acid PRO) & 5.57 \\
8-Hydroxyquinoline (HQ) & 4.8 \\ Gallic acid (GAL) & 3.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Retention time of the phenolic acid standards. Figure 1: Concentration (ppm) of phenolic acids in the aqueous shoot extracts of the rice genotypes: (**a**) Govind; (**b**) UPR-2962-5-2-1, and (**c**) UPR-2992-17-3-1 after treatment with methyl salicylate (MeSA, 1 mM, 2 mM, or 3 mM). The values are means from three replicates. S = syrginic acid, V = vanillic acid, PHB = p-hydroxybenzoic acid, PC = \(p\)-coumaric acid, CAF = caffeic acid, PRO = protocatechuic acid, HQ = 8-hydroxyquinoline, and GAL = gallic acid. In all genotypes, the phenolic acid amount recorded after treatments with 1 mM MeSA was at par with that at 3 mM MeSA, both in shoots and roots. It is likely that 1 mM is a low-dose treatment, whereas 3 mM could be slightly phytotoxic or somehow repress the phenolic acid biosynthesis in plant. We can also speculate that a negative feedback regulation of salicates occurs in rice. Similar increments in phenolic acid contents after the application of signaling compounds were shown by [PERSON] et al. [26] and [PERSON] et al. [30]. These results suggest that MeSA exerted an effect on the phytotoxic potential of rice genotypes in which the allebotathic activity against _E. colona_ increased  
Figure 2: Concentration (ppm) of phenolic acids in the aqueous root extracts of the rice genotypes: (**a**) UPR-2962-5-2-1, (**b**) Govind, and (**c**) UPR-2992-17-3-1 after treatment with methyl salicate (MeSA, 1 mM, 2 mM, or 3 mM). The values are means from three replicates. S = syrigenic acid, V = vanillic acid, PHB = \(p\)-hydroxy benzoic acid, PC = \(p\)-cumaric acid, CAF = caffe acid, PRO = protocatechic acid, HQ = 8-hydroxyquinoline, and GAL = gallic acid. in response to its foliar application, both in competitive and non-competitive genotypes. This increment could be attributed to the well-known role of salicylic acid as an elicitor of the plant's own defense mechanisms toward insect and pathogen attacks, including the increased biosynthesis of allelochemicals [42]. Hence, MeSA can be developed to enhance the allelopathic potential of the crop plants. It has been documented that the weeds compete with the host crop for area, nutrients, water, and sunlight, and this competition results in decreased growth and yield losses in the host plant. These losses can be minimized by the use of competitive genotypes. Moreover, treatments with signaling compounds such as MeSA can further increase the competitiveness of the genotypes against weed species by stimulating the accumulation of the allelochemicals such as phenolic acids. Treatments of rice plants with MeSA improved their growth, productivity, and competitiveness against weeds.