Based on prior knowledge and assuming that IFP (plant height) is positively correlated with grain yield, we can analyze the relationship between IFP and the target variable (grain yield) as follows:

- Low grain yield: Plants with low grain yield may have shorter plant heights. The IFP values for this class could be in the range of 10-40 cm.

- High grain yield: Plants with high grain yield may have taller plant heights. The IFP values for this class could be in the range of 60-90 cm.

Based on this analysis, the dictionary can be generated as follows:

```json
{
	"low": [10.0, 15.0, 20.0, 30.0, 40.0],
	"high": [60.0, 65.0, 70.0, 80.0, 90.0]
}
```