Apple Inc.¡¯s quest to adopt advanced displays for its next-generation iPhone hinges on a single supplier in the Japanese countryside.

Canon Tokki Corp., surrounded by rice fields in the city of Mitsuke in Niigata Prefecture, has a near monopoly on the machines capable of making screens with organic light-emitting diodes, which enable sharp, vibrant displays that use less energy. A unit of Canon Inc., the company of 343 employees has spent more than two decades perfecting the manufacturing equipment used by OLED screen makers.

But there¡¯s a problem: Canon Tokki has a growing backlog even after doubling output in 2016. The potential production bottleneck is raising questions over Apple¡¯s ability to feature OLED displays in next year¡¯s iPhones, and whether the Cupertino, California-based company will be able to line up additional suppliers. The current wait for a machine, which can cost more than ?10 billion ($85 million) each, is about two years.