Mariners call up top prospect Walker

Seattle Mariners pitching prospect Taijuan Walker will make his major league debut on Friday when he starts against the Houston Astros.

Walker, who turned 21 two weeks ago, was officially added to the 25-man roster when the Mariners shipped outfielder Michael Morse to the Baltimore Orioles earlier in the day.

The 6-foot-4 right-hander was the Mariners' first pick in the 2010 MLB Draft, as a supplemental first-round selection (43rd overall). He is considered to be one of the top prospects in baseball, having played in the past two All-Star Futures Games and is listed on as the No. 1 Mariners prospect and No. 4 overall prospect.

Walker has started 25 games for Double-A Jackson and Triple-A Tacoma this season, posting a 9-10 record with a 2.93 ERA and 160 strikeouts over 141 1/3 innings.

Seattle acquired outfielder Xavier Avery in the trade with Baltimore and optioned him as well as pitcher Erasmo Ramirez to Triple-A Tacoma.

The Mariners also selected the contract of Abraham Almonte from Tacoma on Friday.