"I don't like tomato." Incorrect

"I don't like tomatoes" Correct

Same for your pear sentence.

Well, it depends on context and whether you want to understand (or put up with) a bit of common 'lazy English'.

As a sentence all by itself, you would use "I don't like tomatoes".

However, if someone were to ask: "Do you want some of my fun flavored ice cream?" and the ice cream flavor was tomato (yuck), you could answer, "No, I don't like tomato. If you have some pear I'll give it a try!".  NOTE: This is not technically correct if you care about proper grammar. Since 'tomato' and 'pear' are describing something, you really should say what they are describing. Proper grammar would be "No, I don't like tomato ice cream. If you have some pear ice cream I'll give it a try!". Since the 'ice cream' is implied by the initial question, you will probably hear people drop the noun sometimes.

Short answer: Don't use "I don't like tomato". Just be prepared to understand how you might hear it and what it means :)

If you are talking about something you can count (1 pear, 2 pears, 5 tomatoes...) then you use the plural form when you are talking in general.

Do you like pears?

I don't like tomatoes.

One is for plural and the other for singular and yes when you say I dont like tomoatoes it means that you dont like any tomatoes. 

All are correct