## 4 Discussion  
This study demonstrated the inhibitory effect of _S. cereale_ extracts on the growth of different weeds both under in vitro and field conditions. An increase in the concentration of _S. cereale_ (Paldong cv.) leaf extracts (5%) resulted in an intense inhibitory effect on the biomass of _Commelina communis_ callus. Callus growth of _Portulaca oleraca_ and _C. album_ was more resistant than the callus of _C. communis_ to the same amount of leaf extracts. It has been reported that lower inhibitory effects of cover crops are associated with the presence of a strong detoxification mechanism present in the weed species [54]. The growth and development of _Digitaria ciliaris_ and _Amaranthus lividus_ calli were highly sensitive to all concentrations of leaf extracts, as indicated by a lower amount of biomass and higher inhibition rate. In contrast, a lower concentration of _S. cereale_ extracts (0.1%) showed a stimulating effect on callus growth in _C. communis_. These results indicate that the allelopathic effects of _S. cereale_ towards weeds are species specific. Moreover, some of the phenolic compounds present in the plant species have been shown to produce both stimulatory and inhibitory effects on callus growth and proliferation [55]. However, in the present study, callus growth and fresh weight were inversely related to the tested phenolic compound's concentration. A similar observation was also recorded by [PERSON] et al. [56], in which a higher concentration of phenolic compounds suppressed the growth of callus and its biomass. The inhibitory effects of these compounds on the biomass of all weed calli were observed in leaf extraction concentrations as low as \(10^{-5}\) M. Previous studies reported a close association between allelopathic properties and phytochemical exudes from plants [57; 58]. The allelochemicals released from the plant exudes usually inhibit the growth of plant cells by disrupting the cell membrane and cellular components [56]. Phenolic compounds such as _p_-coumaric acid and its various derivatives were found to inhibit photosynthesis enzymatic activities of glucosephosphate isomerase (PGI), 6-phosphate dehydrogenase (G6P-DH), and aldolase (AID) in the oxidative pentose phosphate pathway (OPPP), causing a detrimental effect on plant growth [59]. It has been suggested that _p_-coumarin developed a waterstress-like situation in plants by accumulating a higher osmolality. Furthermore, _p_-coumarin is known for its inhibitory effect on seed germination and plant growth, and it also causes a deleterious effect on root growth by changing its morphological and physiological structure [60; 61; 62]. It has been argued that quercetin can affect the electron transport system (ETS), causing inhibition of substrate  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{ \begin{tabular}{c} **Amunout of** \\ **Cover Crops** \\ **(Kg)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Types of** \\ **Cultivation** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Method of** \\ **Planting** \\ **_P. frutscenes_** \\ \end{tabular}  } & \multicolumn{2}{c}{**Grass Weeds**} & \multicolumn{2}{c}{**Broadleaf Weeds**} \\ \cline{5-8}  & & & **P.** & **Fresh Weight** & **Inhibitory** & **Fresh Weight** & **Inhibitory** \\ \hline \multirow{4}{*}{8} & \multirow{2}{*}{ \begin{tabular}{c} Tillage \\ No-tillage \\ LPD \\ No-tillage \\ LPD \\ \end{tabular}  } & \begin{tabular}{c} HPD \\ LTD \\ \end{tabular}  & \begin{tabular}{c} 311.20 \(\pm\) 10.00 \({}^{\text{g}}\) \\ 355.80 \(\pm\) 12.50 \({}^{\text{h}}\) \\ 202.10 \(\pm\) 5.00 \({}^{\text{a}}\) \\ 304.20 \(\pm\) 7.50 \({}^{\text{f}}\) \\ \end{tabular}  & \begin{tabular}{c} 50.92 \(\pm\) 5.00 \({}^{\text{b}}\) \\ 43.89 \(\pm\) 3.50 \({}^{\text{a}}\) \\ 68.13 \(\pm\) 4.99 \(\mathrm{g}\) \\ 52.03 \(\pm\) 3.00 \({}^{\text{c}}\) \\ \end{tabular}  &