Based on prior knowledge, the feature "Cultivar" can be analyzed in relation to the task of predicting the grain yield of the soybean cultivar. It is important to note that the feature "Cultivar" alone may not provide enough information to accurately predict the grain yield, as other factors such as environmental conditions, disease resistance, and agronomic practices can also influence the yield. Therefore, we can only analyze the relationship between "Cultivar" and the target class (low or high grain yield) based on the provided data.

To create the dictionary as requested, we can analyze the relationship by comparing the values of the feature "Cultivar" for the different target classes.

Here is the dictionary:

```json
{
	"low": ["LTT 7901 IPRO", "EXPANDE LTT 8301 IPRO", "FTR 3868 IPRO", "MANU IPRO", "NEO 760 CE", "74K75RSF CE", "96R29 IPRO"], 
	"high": ["FTR 3190 IPRO", "FTR 4288 IPRO", "NK 8770 IPRO", "MONSOY M8606I2X", "M 8644 IPRO", "ADAPTA LTT 8402 IPRO", "98R30 CE", "FORTALEZA IPRO", "MONSOY 8330I2X", "SUZY IPRO", "TMG 22X83I2X", "EXPANDE LTT 8301 IPRO", "FORTALECE L090183 RR", "83IX84RSF I2X", "82HO111 IPRO - HO COXIM IPRO", "82I78RSF IPRO", "SYN2282IPRO", "ATAQUE I2X", "NK 8100 IPRO", "FTR 4280 IPRO", "LYNDA IPRO", "BRASMAX OLIMPO IPRO", "LAT 1330BT", "FTR 3179 IPRO", "97Y97 IPRO", "BRASMAX BÔNUS IPRO", "PAULA IPRO", "NEO 790 IPRO", "GNS7900 IPRO - AMPLA", "79I81RSF IPRO", "ELISA IPRO", "NK 7777 IPRO", "77HO111I2X - GUAPORÉ", "GNS7700 IPRO"]
}
```

Please note that the provided list of cultivars may not include all possible cultivars, and the analysis is based on the given data.