TOKYO — Japan's Crown Prince Naruhito said Wednesday he hopes his upcoming trip to Ghana and Kenya will deepen ties between Japan and the African nations as well as his understanding of problems facing the continent.

Naruhito, heir to the world's oldest hereditary monarchy, won't be making the March 6-15 trip with Princess Masako, who withdrew from most of her official duties several years ago because of a nervous disorder attributed to difficulties adjusting to palace life and the pressure to bear a son to continue the imperial line.

In Ghana, the crown prince plans to attend a medical symposium held in honor of Hideyo Noguchi, a Japanese doctor who died in Accra, the Ghanian capital, in 1928 while researching a cure for yellow fever.

Noguchi's face appears on the Japanese 1,000 yen bill.

This will be Naruhito's first trip to sub-Saharan Africa. Overseas trips by members of the imperial family are one of their important duties, which under the post-World War II constitution are largely ceremonial.

"I'd be happy if this trip can strengthen the friendly ties between Japan and Africa even a little bit," he told reporters during a rare and carefully orchestrated news conference at the Akasaka Palace in central Tokyo.

Naruhito, 50, said he hopes to experience some of Kenya's "magnificent nature" and learn more about the difficulties of gaining access to clean water. He has a special interest in water because he is honorary president of U.N. Secretary-General's Advisory Board on Water and Sanitation.

"I have heard that both countries are held up as success stories in dealing with water issues, so I hope to learn from people involved and see further development on the water issues," he said.

He said both he and Masako were disappointed that she won't be joining him. "In consulting with doctors, it was decided that I would go alone," he said. Masako is appearing a bit more in public recently after rarely emerging from the palace for several years. Her last official trip abroad was December 2002 when the royal couple visited Australia and New Zealand.

Many speculate Masako had felt stress from the pressure to produce a male heir. Under a post-World War II law, only males are allowed to assume the Chrysanthemum Throne.

After suffering a miscarriage in 1999, Masako had a daughter, Aiko, in 2001. That fanned a movement to change the law to allow the girl to succeed her father. But the succession crisis was forestalled when Princess Kiko, the wife of Naruhito's younger brother, Prince Akishino, had a baby boy in 2006. The boy, Hisahito, is now third in line to the throne.