Based on the provided feature description, I will analyze the relationship between the "Cultivar" feature and the target variable of grain yield (low or high).

To analyze the relationship, I will look for patterns or trends in the values of the "Cultivar" feature that may indicate whether the grain yield is low or high. 

From the given information, there are no direct clues or specific details about the relationship between the "Cultivar" feature and grain yield. Therefore, I cannot make any certain conclusions or predictions based solely on this information.

However, I will examine the available data and generate a dictionary based on the given format, keeping in mind that these are general observations and not concrete predictions:

```json
{
    "low": ["NEO 760 CE", "MANU IPRO", "77HO111I2X - GUAPORÉ", "NK 7777 IPRO", "GNS7900 IPRO - AMPLA"],
    "high": ["FTR 3190 IPRO", "FTR 4288 IPRO", "NK 8770 IPRO", "MONSOY M8606I2X"]
}
```

Please note that the list of cultivars for each target class is based on general observations and may not accurately reflect the relationship between the "Cultivar" feature and the grain yield. Further analysis and additional data may be needed for more accurate predictions.