# Elicitation of the Allelopathic Potential of Rice by Methyl Salicylate Treatment
## 3 Results and Discussion
### Phenolic Acids  
The phenolic acid content of the genotypes UPR-2992-17-3-1, UPR-2962-6-2-1, and Govind after treatment with 1 mM, 2 mM, or 3 mM MeSA was analyzed by high-performance liquid chromatography \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Genotypes**} & **MeSA** & **E. colona** & **E. colona** & **E. colona Root** & **E. colona** & **Shot** \\  & **(mM)** & **Germination (\%)** & & **Length (cm)** & & **Length (cm)** \\ \hline \multirow{4}{*}{UPR-2992-17-3-1} & & Shoot & Root & Shoot & Root & Shoot & Root \\  & & extract & extract & extract & extract & extract & extract \\ \cline{2-7}  & Control & 86.3 & _77.7_ & 6.8 & 6.8 & 5.8 & 5.9 \\  & 1 & 77.3 & 70.0 & 6.1 & 6.4 & 5.1 & 5.5 \\  & 2 & 69.7 & 64.7 & 5.5 & 5.9 & 4.5 & 5.3 \\  & 3 & 63.7 & 53.0 & 5.2 & 5.4 & 4.2 & 5.1 \\ \hline \multirow{4}{*}{UPR-2962-6-2-1} & Control & 65.0 & 61.0 & 6.4 & 6.7 & 5.7 & 5.8 \\  & 1 & 59.0 & 54.0 & 5.5 & 5.5 & 5.0 & 5.1 \\ \cline{2-7}  & 2 & 46.7 & 42.3 & 4.9 & 4.7 & 4.0 & 4.6 \\  & 3 & 38.0 & 35.7 & 4.1 & 4.2 & 3.4 & 3.5 \\ \hline \multirow{4}{*}{Govind} & Control & 58.3 & 57.7 & 5.9 & 5.9 & 5.5 & 5.8 \\  & 1 & 50.7 & 48.3 & 5.1 & 5.4 & 4.8 & 5.3 \\  & 2 & 43.3 & 39.0 & 4.4 & 4.7 & 4.1 & 4.6 \\  & 3 & 32.3 & 30.0 & 4.0 & 4.2 & 3.3 & 3.6 \\ \hline \multirow{4}{*}{LSD (\(p\leq 0.05\)) Genotypes (G) Methyl salicate (MeSA) & 4.04 & 2.83 & 0.80 & 0.81 & 0.80 & 0.64 \\  & 5.50 & 3.84 & 1.08 & 1.11 & 1.09 & 0.87 \\ \cline{1-1}  & 6.35 & 4.44 & 1.25 & 1.28 & 1.26 & 1.00 \\ \cline{1-1}  & 6.3 \(\times\) MeSA & 11.0 & 7.69 & 2.17 & 2.22 & 2.18 & 1.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effects of shoot and root extracts obtained from rice genotypes treated with 1 mM, 2 mM, and 3 mM concentrations of methyl salicate (MeSA) on percent germination, root and shoot length of the weed _Echinochloa_ colona. (HPLC) using syringe acid (S), vanillic acid (V), p-hydroxybenzoic acid (PHB), p-coumaric acid (PC), caffeic acid (CAF), protocatechuric acid (PRO), 8-hydroxyquinoline (HQ), and gallic acid (GAL) as standards (Table 3). Phenolic acids with different structures and modes of action show variable phytotoxic activity [39]. All phenolic acids detected in the three rice genotypes after MeSA exposure are among the main phytotoxic compounds isolated from the aqueous extracts of allelopathic plants [39; 40]. They demonstrated significant inhibition of the _Lactuca sativa_ seed germination compared to the control at 10 ppm or at 1 mM and 2 mM concentrations [39]. Differently, [PERSON] and coworkers [41] reported that some acids, namely p-hydroxybenzoic, vanillic, gallic, and caffeic acids, have not proved capable of significantly reducing _L. sativa_ germination both at 100 \(\upmu\)g/mL and 250 \(\upmu\)g/mL. On the contrary, caffeic acid showed a particular behavior stimulating seedling growth, particularly the root elongation of L. sativa, in the concentration range 50-500 \(\upmu\)g/mL [41]. Lastly, the phytotoxicity of the compounds involved in allelopathic effects depends upon the target species and, overall, their chemical interference is probably based upon a combination of phytotoxic metabolites. Studies on phenolic acid mixtures have shown that individual components can be additive when being evaluated for phytotoxic affects. However, further research is still needed to find evidence for their synergistic activities [41]. In our work, all MeSA treatments enhanced the production of these compounds in the analyzed samples. In particular, the 2-mM concentration of MeSA had the largest effect. In the shoot extracts of competitive genotype UPR-2962-6-2-1, the resulting increase of S, V, PHB, PC, CAF, PRO, and GAL was 1.8-, 2.1-, 2-, 1.6-, 1.5-, 2.1-, and 1.6-fold, respectively, compared to control (Figure 1a). In Govind genotype S, V, PHB, PC, PRO, and HQ increased by 1.8-, 2.1-, 1.6, 1.5-, 1.9-, and 1.8-fold, respectively (Figure 1b).