First, the meaning is different
1.potato means:? Potato; potato
2.tomato means: Tomato; tomato
Second, the usage is different
1.potato Usage: It means "potato, potato" and can be used as an uncountable noun or a countable noun. Used metaphorically, it can be interpreted as "insignificant person or thing".
Example:
The potato is a vegetable, not a fruit.
Potato is a vegetable, not a fruit.
2.tomato usage: it basically means "tomato, tomato", which can be used as a countable noun or an uncountable noun. Tomato can be used as an attribute before other nouns.
Example:
Would you like some tomato paste?
Do you want tomato sauce?
Third, the focus is different
1.potato Focus: Used in the simple present tense.
2.tomato focus: used in the simple present tense or the simple future tense.