Based on the available information, it is not possible to directly determine the relationship between the "Cultivar" feature and the target variable of grain yield. The feature descriptions only provide information about maturation group, seeds per meter/linear, and density per meter/linear, which may not be directly related to the grain yield.

To create the dictionary, I will assume the following:
- High grain yield indicates a high value for the target variable.
- I will consider the top 50% of the available cultivars (based on an assumed grain yield ranking) as "high" grain yield and the remaining cultivars as "low" grain yield.

Here is the generated dictionary:

```json
{
	"low": ["MONSOY M8606I2X", "M 8644 IPRO", "FTR 4280 IPRO", "LYNDA IPRO", "ELISA IPRO", "MANU IPRO", "FTR 3868 IPRO"],
	"high": ["NEO 760 CE", "74K75RSF CE", "96R29 IPRO"]
}
```