Based on my prior knowledge, the MHG (Thousand seed weight) feature is likely to have a positive relationship with the grain yield of the soybean cultivar. Generally, higher seed weight is associated with higher grain yield. 

To generate the dictionary, I will need to analyze the feature values for the target classes 'low' and 'high'. Here are the typical MHG values for each target class:

For the 'low' target class:
1. 150.0
2. 160.0
3. 170.0
4. 180.0
5. 190.0

For the 'high' target class:
1. 200.0
2. 210.0
3. 220.0
4. 230.0
5. 240.0

Based on these values, I can create the dictionary:

```json
{
	"low": [150.0, 160.0, 170.0, 180.0, 190.0],
	"high": [200.0, 210.0, 220.0, 230.0, 240.0]
}
```

Please note that these values are just examples and may not accurately represent the entire range of MHG values for each target class. Further analysis and data exploration would be required to determine the actual ranges.