The NPA attack reportedly stemmed over Palma Gils refusal to pay a permit-to-campaign fee to the New Peoples Army (NPA).
Communist rebels have been demanding at least P50,000 for mayoralty candidates and as much as P1.5 million for congressional candidates to be able to campaign in so-called NPA-influenced areas.
The Southern Mindanao police said a soldier detailed as one of Palma Gils security escorts, was wounded in the attack but has been declared out of danger.
The governors group was reportedly on their way to a campaign rally in Banganga town when they were fired upon when they reached Barangay Campawan.
Meanwhile, a congressional candidate in Davao del Sur said he has received death threats in the form of text messages from unknown sources.
Lawyer Dominador Carillo, who is running for Congress in the second district under the banner of Lakas-CMD, said the text messages warned him to stop delivering campaign speeches.