# Natural Salicylaldehyde for Fungal and Pre- and Post-Emergent Weed Control
## 3 Results and Discussion
### Pre- and Post-Emergent Herbicidal Activity of SA
#### 3.3.1 Pre-Emergent Herbicidal Activity of SA  
Initially, the pre-emergent herbicidal activity of SA was investigated against _Brassica rapa_ var. _pekinensis_ seeds on PDA (Petri plates, 100 mm \(\times\) 15 mm). _Brassica_ spp. is listed  
Figure 2: A representative bioassay showing the adjuvant activity of SA fumigant that overcomes fluidoxonil tolerance of mitogen-activated protein kinase (MAPK) mutants of _Penicillium expansum_ (FR3). W2, _P. expansum_ parental strain. The upper panel of each plate shows fungal growth (radial growth) or no growth (empty); the lower panel of each plate shows the filter (2.5 cm) w/o (DMSO only; no treatment control) or w/ SA (0.12 M).  
as a restricted or prohibited noxious weed seed in the states of Arizona and Michigan, respectively, in the United States [32]. _Brassica_ spp. may become weedy or invasive by producing allebotathic chemicals, which prevent the germination of native plants or plants in cultivated fields. Therefore, if not adequately managed, _Brassica_ spp. could displace desirable vegetation [32]. Walnut shell particles saturated with SA (concentration: 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 M) were placed on the center of PDA (duplicate plates), and seed germination/growth was monitored for 10 days at 22 \({}^{\circ}\)C (12 h light/12 h dark cycle). SA emitted from the nutshell vehicles completely inhibited the germination of _Brassica_ seeds at as low as 0.15 M of SA (Table 2).  
Plant seeds are also commonly contaminated with environmental fungi and other microbes [33; 34]. However, the germination/growth of microbial contaminants associated with the surfaces of _Brassica_ seeds and nutshell particles was completely prevented w/ SA at or above 0.3 M (Table 2) (Figure 3; representative bioassay w/ 0.0 and 0.3 M of SA).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**SA (M)**} & **\# of Seeds** & **\# of Seeds** & **Level of Nutshell** \\  & **Germinated** & **Contaminated w/ Fungi** & **Contamination w/ Fungi 1** \\ \hline
0.00 & 10, 10 & 2, 1 & ++++, +++ \\
0.05 & 4, 3 & 1, 0 & +++, ++ \\
0.10 & 1, 0 & 1, 0 & +, - \\
0.15 & 0, 0 & 2, 0 & +, + \\
0.20 & 0, 0 & 0, 0 & +, - \\
0.25 & 0, 0 & 1, 0 & +, - \\
0.30 & 0, 0 & 0, 0 & -, - \\
0.35 & 0, 0 & 0, 0 & -, - \\
0.40 & 0, 0 & 0, 0 & -, - \\
0.45 & 0, 0 & 0, 0 & -, - \\
0.50 & 0, 0 & 0, 0 & -, - \\ \hline \hline \end{tabular}  
* Level of nutshell particle contamination: +++, High; ++, Medium; +, Low; -, No contamination.  
\end{table}
Table 2: Kinetics of pre-emergent herbicidal activity of SA tested against _Brassica_ rapa var. _pckinensis_ (total 10 seeds placed/plate) determined in duplicated plates. SA delivery vehicles: walnut shell particles 0.3 g/plate.  
Figure 3: SA (0.3 M) prevented the germination of _Brassica_ seeds, where the SA further eliminates seed- and nutshell-borne fungal pathogens.  
Similar assays were performed on different weed seeds, including _Centaurea solstitialis_, _L. ovatus_, _Salsola tragus_, _Genista monspessulana_, and _S. scorparium_ (see Table 1 for seed characteristics). It was determined that the germination of the seeds as well as that of the fungi associated with the surface of test seeds, was completely prevented at 0.25 to 1.6 M of SA, depending on the types of seeds investigated (Table 3).  
The pre-emergent herbicidal activity of SA was tested further in Magenta vessels, where 10 seeds of _L. ovatus_ were placed per vessel supplemented with MS (0.5\(\times\)). As shown in Figure 4, the germination of _L. ovatus_ seeds exposed to 0.8 to 1.6 M SA vapor was completely inhibited, while those in the control boxes (w/ or w/o walnut shell particles) still germinated.