It's estimated that candidates in Philippine presidential elections typically spend around 60 billion pesos on campaign expenses. In the 2016 election, Duterte officially ranked fourth in spending among five candidates.
While it's true that he spent less because he was a dark horse candidate from the Mindanao region, Duterte still spent a considerable amount of money.
The top official donor was Antonio Floirendo Jr., the son of Antonio Floirendo Sr., a banana magnate from Davao.
The recorded donation was 75 million pesos, which is 1.54 billion Korean won, but the actual amount spent is unknown.
There's no limit on individual donations as long as the total amount stays within the allowed limit.

Antonio Floirendo is the heir to Tadeco, the Philippines' largest banana producer.
Tadeco exports 450,000 tons of bananas annually from its 20 million pyeong farm.
Of this, 15% is exported to Korea.
The reason you don't see the Tadeco brand at E-Mart is because they export under the Del Monte brand. The farm size is comparable to that of Ulleungdo Island.

Ultimately, Tadeco's money played a significant role in Duterte's election, meaning Korean banana consumers contributed to his victory to some extent.

During the Marcos dictatorship, Tadeco leased land from the state. They reclaimed what was then mostly swampland, utilizing prisoners from Davao's penitentiary as the primary labor force.
With the land almost free and labor virtually free, becoming wealthy was only a matter of time.

Some might think that bananas are heavily sprayed with pesticides and harvested when fully ripe and yellow, then treated with chemicals for export.
While pesticides are used, bananas are a fruit with a thick peel, and they arrive at Busan Port by ship while still unripe. If harvested when fully ripe and yellow, they would already be rotten by the time they reach Busan.
They are ripened using ethylene gas just before sale, making bananas a relatively safe fruit.
The ethylene gas naturally produced by bananas is the same as the artificially applied ethylene gas.

Those who consume a lot of Del Monte bananas in Korea have, in a way, supported Duterte. Observing the packing process, it seems wax is applied to the stem to prevent ethylene gas from escaping during transport.

Indeed, when Duterte visited Korea this year, the only company he visited was E-Mart. 73% of E-Mart's banana sales come from Philippine bananas.
This once again proves that nothing in this world is free.
It's interesting that he visited E-Mart instead of Samsung Electronics during his visit to Korea.
Source https://m.blog.naver.com/daturada73/221365262626
What I want to say is that it's amazing to realize that such a complex equation can be hidden behind a single banana. It's also intriguing why foreign leaders visit E-Marts found in every neighborhood, rather than the heavy chemical industrial complexes of Ulsan or Pohang, or the Hynix and Samsung facilities in Yongin and Suwon, which are major industrial hubs in Korea.