A brief history of the Chazon Ish Esrog
Chazon Ish esrogim are grown in two main types: the Halperin Chazon Ish, and the Lefkowitz Chazon Ish.
Esrogim are not native to Eretz Yisroel, however it is believed to be the oldest cultivated fruit in the country dating back to around the year 500 BCE.
In the middle of the 19th-century, Balady esrogim (commonly referred to these days as Chazon Ish esrogim) were exported from Eretz Yisroel in significant volumes to the European market, however there was a machlokes regarding the kashrus of the esrogim with many believing the esrogim trees had been grafted and were not kosher for use.
When the Chazon Ish (Rabbi Avrohom Yeshaya Karelitz) arrived in Eretz Yisroel he investigated the kashrus of the esrogim trees. Upon finding a kosher tree, the Chazon Ish famously held up an esrog and pronounced "This is an esrog". The seeds from that esrog were planted by R’ Michel Yehuda Lefkowitz and have given rise to the Lefkowitz type of esrog. The Chazon Ish also gave R’ Yakov Halperin, founder of Zichron Meir in Bnei Brak, the seeds to plant a second strain.
The importance of the difference between the two strains for the Chazon Ish remains unclear and the special status of these groups of esrogim is solely due to the fact that the Chazon Ish assured their authenticity as not being the product of a grafted tree.