Shown from left, Joan Risley, 67, of Scottsdale, Ariz.; Roger Risley, 62, of Port Townsend, Wash.; Chris Wagner, 60, of Sacramento, Calif.; and Prudence Hopkins, 57, of Spotsylvania, Va., gather in advance of the the annual AARP National Spelling Bee Thursday Aug. 9, 2012, in Cheyenne, Wyo. (AP Photo/Mead Gruver) (Mead Gruver/AP)

Michael Petrina Jr., 67, of Arlington County was in Wyoming over the weekend where, of all things, he was asked to spell rhizoctonia.

This might have flummoxed most people, but not Petrina, a retired lawyer and lobbyist, who had seen the word before. He spelled it correctly and won a national spelling bee sponsored each year by AARP.

The competition was started in 1996 by members of AARP in Cheyenne, where it is still held. The idea, said Joanne Mai, a spokeswoman for the annual bee, is to encourage people to keep their minds sharp as they grow older.

The bee, which is open to people who are at least 50 on the day of the competition, typically draws 40 or 50 participants.

A handful enter on a lark. But most, Mai said, are “top-notch spellers.”

As is Petrina, apparently, who also won the competition in 2009.

As with champions in almost any field, Petrina has a way of preparing for a contest.

Taking in hand the dictionary from which all the bee’s words are drawn, he has transcribed “about 20,000” on index cards.

And, he said, he “did do a little cramming before the contest.”

Among the words he wrote down, thinking he might someday be called on to spell it, was rhizoctonia — a type of imperfect fungus.

It is not a word that everybody sees every day. If any indication were needed, it appears to show that competitors are not given an easy time of it in deference to their age.

Even preparation and a powerful memory have not guaranteed success to Petrina.

His victory this year came in his sixth year in the contest. He has finished as low as third, and was the runner-up last year, he said.

A competitive speller as a youngster in western New York, he began to compete anew in recent years, and has found it useful.

For example, he said, he has learned many new words and has become more familiar with words that have entered English from foreign languages. And, he said, as the originators of the competition had hoped, he found it “good mental exercise.”

By curious coincidence, a woman from the Fredericksburg area, who is related to Petrina but had never met him, decided to enter the contest this year with three of her siblings.

They were looking for something to do for the fun of it, said Prudence R. Hopkins, who is a chaplain at Mary Washington Hospital. Although she had not met her cousin, she knew of him and described him as “quite a sharp guy.”

“I did not do well at all,” she said. But, she said, a sister passed the first stage of the contest, a written exam, and went on to the oral finals.

In the finals, Petrina prevailed, according to the contest spokeswoman, in the 47th round.

The winner’s prize included $1,000 and a five-year AARP membership.