Based on the provided feature descriptions, I can analyze the relationship between the "Cultivar" feature and the target variable "grain yield" to determine how the feature is related to the task of predicting whether the grain yield will be low or high.

To perform this analysis, I would need information about the historical grain yields associated with each cultivar in order to identify patterns or trends. Without this information, I can only make assumptions based on the given feature descriptions.

From the available data, it is not possible to directly determine which cultivars will result in a low or high grain yield. However, we can look for potential correlations between the cultivar names and the other provided information (maturation group, seeds per meter/linear, density per meter/linear) to make an inference.

To create the dictionary with the requested format, I will assume that the cultivars with higher values for "Seeds per meter/linear" and "Density per meter/linear" may have a higher chance of resulting in a high grain yield, while cultivars with lower values may have a higher chance of resulting in a low grain yield. 

Based on this assumption, I will categorize the cultivars accordingly:

```json
{
	"low": [
		"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",
		"ATAQUE I2X",
		"FTR 4280 IPRO",
		"LYNDA IPRO",
		"FTR 3179 IPRO",
		"NEO 760 CE",
		"74K75RSF CE"
	],
	"high": [
		"FTR 3190 IPRO",
		"FTR 4288 IPRO",
		"82HO111 IPRO - HO COXIM IPRO",
		"82I78RSF IPRO",
		"SYN2282IPRO",
		"NK 8100 IPRO",
		"LAT 1330BT",
		"97Y97 IPRO",
		"BRASMAX BÔNUS IPRO",
		"PAULA IPRO",
		"NEO 790 IPRO",
		"LTT 7901 IPRO",
		"GNS7900 IPRO - AMPLA",
		"79I81RSF IPRO",
		"ELISA IPRO",
		"GNS7700 IPRO",
		"FTR 3868 IPRO",
		"MANU IPRO",
		"NK 7777 IPRO",
		"77HO111I2X - GUAPORÉ",
		"96R29 IPRO"
	]
}
```

Please note that these categorizations are based on assumptions and limited information. The actual relationship between the "Cultivar" feature and the task of predicting the grain yield can only be accurately determined with additional data and analysis.