B”H If someone has fruit of unknown origin, may they eat it by assuming it did not come from Israel? Also, is there any obligation to tithe a single piece of fruit that one does know comes from Israel (I am still trying to learn these laws…)
A person in chutz la’aretz does not have to assume that the fruit of unknown origin is from Israel, as most fruit imported in foreign countries is not from Israel. This also applies to tithing even one fruit.
As a side point tithing when tithing one fruit, there is a need to have what is called a “peruta chamura” -a special coin that was once used to redeem a certain type of ma’aser sheinei, and therefore when you have fruit to tithe make sure that each type of fruit has a value of overone about 30 cents.