## 3 Results and Discussion
### Promoting Effect of Diallyl Disulfide  
Results showed that the growth of tobacco seedlings treated with the 1000-times and 500-times dilutions of DADS showed no significant changes, and the root length increased significantly compared to the control. However, tobacco seedlings treated with the 200-times and 100-times dilutions of DADS were obviously weaker. Furthermore, the leaf growth was inhibited, wilting appeared, the root length was significantly longer and sparser compared to the control, and the root system was poorly developed (Table 4). As such, the results indicated that DADS promoted root development of tobacco seedlings at low concentrations, but inhibited development at high concentrations. This finding was  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Treatment**} & \multicolumn{2}{c}{**Root Irrigation Effect**} & \multicolumn{2}{c}{**Fumigation Effect**} \\ \cline{2-5}  & **Disease Index** & **Control Effect (\%)** & **Disease Index** & **Control Effect (\%)** \\ \hline GEO 1000 1  & 66.67 \(\pm\) 1.10 b & 19.40 \(\pm\) 0.53 d & 48.15 \(\pm\) 1.33 b & 41.80 \(\pm\) 0.265 c \\ GEO 500 2  & 44.44 \(\pm\) 2.42 d & 46.35 \(\pm\) 1.70 b & 41.98 \(\pm\) 1.39 c & 49.27 \(\pm\) 0.51 b \\ DADS 1000 3  & 51.85 \(\pm\) 2.02 c & 37.36 \(\pm\) 1.00 c & 46.91 \(\pm\) 1.85 bc & 43.33 \(\pm\) 0.93 c \\ DADS 500 4  & 41.48 \(\pm\) 1.21 d & 49.87 \(\pm\) 0.31 a & 33.33 \(\pm\) 2.42 d & 59.80 \(\pm\) 2.01 a \\ CK 5  & 82.72 \(\pm\) 1.91 a & - & 82.72 \(\pm\) 1.91 a & - \\ \hline \hline \end{tabular}  
* 1000-times dilution of garlic essential oil diluted with 1% DMSO, 5  
DMSO, 6  
* 1000-times dilution of DADS diluted with 1% DMSO, 7[ENDFOOTNOTE]  
\end{table}
Table 2: The control efficacy of the garlic essential oil and diallyl disulfide (DADS) treatments against tobacco black shank.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Treatment** & **Copies of Root Irrigation Effect** & **Copies of Fumigation Effect** \\ \hline GEO 1000 1  & 558,251.04 \(\pm\) 9385.42 b & 15,531.74 \(\pm\) 617.53 d \\ GEO 500 2  & 38,276.60 \(\pm\) 2752.51 d & 1413.87 \(\pm\) 98.33 d \\ DADS 1000 3  & 238,512.00 \(\pm\) 22,176.61 cd & 4623.86 \(\pm\) 246.49 d \\ DADS 500 4  & 62,955.76 \(\pm\) 80.94 d & 752.19 \(\pm\) 2.50 d \\ CK 5  & 9,234,399.25 \(\pm\) 324,740.51 a & 9,234,399.25 \(\pm\) 324,740.51 a \\ \hline \hline \end{tabular}  
* 1000-times dilution of garlic essential oil diluted with 1% DMSO, 2  
\end{table}
Table 3: DNA copies of _P. nicotianae_ treated with garlic essential oil and DADS.  
consistent with that of [PERSON] et al. (2019). [PERSON] et al. (2019) suggested that DADS had biological functions in plant root development and offered insight into the mode of action for this particular allelochemical of garlic. The effects were dose-dependent, with low concentrations having a promotional effect and high concentrations having an inhibitory effect on root growth. DADS actively influenced mitotic indexes and genes related to mitotic cell division, such as CDKA and CDKB. Nonetheless, it is bioactive in modulating functional plant hormones such as IAA, GA3, ABA, and CTK.  
Values are the means of three replicates \(\pm\) SD. Values within the same column followed by different lowercase letters are significantly different (\(p<0.05\)).