NOIDA, India—Amazon.com Inc. and Walmart Inc. are betting billions to face off in India, but their mightiest rival might be a ubiquitous local champ: the mom-and-pop store.
Tiny stores known as kiranas dot every Indian street, village and slum. Usually family-run, these micro-businesses range from street vendors selling vegetables to shops the size of a one-car garage. They pay low wages and have little or no rent, which helps keep costs down. And since they cater largely to neighborhood populations, many offer instant delivery,...