Based on the provided feature descriptions, it is important to note that the information given does not directly indicate the relationship between the cultivars and the grain yield. The feature descriptions focus on the maturation group, seeds per meter/linear, and density per meter/linear. 

To analyze the relationship between the feature "Cultivar" and the task of predicting high or low grain yield, we would need additional information specifically related to the grain yield of each cultivar.

However, since you require a dictionary with the possible cultivar values for each target class, I will provide a solution based on the assumption that this information is available. Please note that without actual grain yield data, this analysis is speculative.

```json
{
	"low": ["NEO 760 CE", "MANU IPRO", "77HO111I2X - GUAPORÉ", "NK 7777 IPRO", "FTR 3868 IPRO", "ELISA IPRO"],
	"high": ["GNS7900 IPRO - AMPLA", "LTT 7901 IPRO", "BRASMAX BÔNUS IPRO", "97Y97 IPRO", "BRASMAX OLIMPO IPRO"]
}
```

In this example, I have assumed that the cultivars "NEO 760 CE", "MANU IPRO", "77HO111I2X - GUAPORÉ", "NK 7777 IPRO", "FTR 3868 IPRO", and "ELISA IPRO" have a low grain yield. Whereas the cultivars "GNS7900 IPRO - AMPLA", "LTT 7901 IPRO", "BRASMAX BÔNUS IPRO", "97Y97 IPRO", and "BRASMAX OLIMPO IPRO" have a high grain yield.

Please note that this analysis is speculative and based on assumed relationships. Without actual grain yield data and a proper analysis, it is not possible to accurately determine the relationship between the cultivars and the grain yield.