KISSIMMEE, Fla. -- Jacob Turner made his final audition for a spot in the Marlins' starting rotation Sunday afternoon, and the results were less than encouraging.

Pitching under dark clouds that gave way to rain as soon as he left the mound, Turner allowed four runs on five hits, four walks and a long home run to center field while striking out one over 4 2/3 innings against the Astros at Osceola County Stadium. He threw 85 pitches, 47 for strikes.

Manager Mike Redmond said the Marlins would meet Sunday night to finalize the plans for their starting rotation, which should be announced as soon as Monday. Though nothing is official yet, it would be hard to imagine Turner making the cut at this point.

If Turner is not part of the rotation, veteran Kevin Slowey will likely become the fifth starter. Slowey is scheduled to start Wednesday against the Red Sox, after lefty Wade LeBlanc and right-hander Henderson Alvarez, which is exactly where he would line up in the Marlins' starting rotation.

Turner would start the season with Triple-A New Orleans after a spring in which he's given up 14 earned runs on 18 hits and nine walks over 13 innings.

"I think the most important thing is just continue to pound the strike zone. The stuff's there. He's got good stuff. It's just consistency," Redmond said. "He's 21 years old. That's the biggest thing to being successful in the big leagues is the consistency of pounding the strike zone, being able to consistently deliver your pitches. Everybody works on that, especially the young guys.

"That's what happens. You never know with young players. They could look great one day and really struggle over the course of time. That's the beauty of the big leagues. The guys who are great players are so consistent day in and day out, year after year after year. The great pitchers continue to get better and they always seem to find a way no matter how many years they've pitched -- find another pitch or another way to pitch or another way to approach hitters -- and that's why stay around for so long. So much of it is just experience."

Redmond said before Sunday's game that Slowey has been stretched out enough this spring to start in the regular season in the event Turner doesn't make the rotation. If Turner somehow ends up winning the fifth-starter battle despite his poor spring, Redmond hinted that Slowey could make the Opening Day roster as the long man.

But that role wouldn't suit Turner, a highly ranked prospect who was brought in last year in the deal that sent Omar Infante and Anibal Sanchez to Detroit. His future is in the rotation, and a reliever's workload could hamper his development.

Turner repeatedly said he has tried to look on the bright side of everything that's happened this spring, from his rough start Sunday to his mostly disappointing Spring Training performance. To that end, he was pleased that he managed to last 4 2/3 innings without feeling comfortable on the mound.

"I was just kind of battling. I felt like, early on, obviously, there were some pitches that I would've liked to have been in a little bit different places," Turner said. "Kind of as the game progressed, I got a little more comfortable out there. Not every day you're going to have your best stuff, so you've just got to go out there and compete with what you've got."

But he experienced the same failure to pound the strike zone that's plagued him all spring. He walked the leadoff hitter in each of his first three innings, and two of those runners scored. Rick Ankiel walked to begin the second and scored on a double by Fernando Martinez. Turner then walked Jose Altuve to lead off the third and served up a homer to Brett Wallace that bounced off a light tower just past the 410-foot marker in center field.

Turner went on to work a scoreless fourth and recorded two quick outs in the fifth before giving up a single to Ankiel. With that, he had reached his pitch limit and exited the game. He wouldn't have spent any more time on the mound anyway, as reliever Zack Phillips made only two warmup pitches before a torrential downpour sent both teams off the field and ended the game.

"Obviously the walks are a concern," Redmond said. "The last couple innings, he was better. I think he came out and looked like his velocity was up. But obviously the biggest thing that we've talked about all spring is we've got to pound the strike zone and get ahead of hitters. We're not a team that's going to be able to afford to walk guys. When you walk guys, the big guys behind them make you pay for it. That's kind of what happened in those couple innings."

Over the past two seasons, Turner has posted a 2.85 ERA over 18 Triple-A starts. Meanwhile, he's 2-6 with a 5.19 ERA in 13 Major League starts. Everything about his pedigree suggests he'll someday become the kind of consistent big league pitcher Redmond talked about Sunday.

But if this spring has been any indication, he's not quite there yet, and the Marlins could make that official by sending him back to Triple-A.

"No matter where I'm pitching, I'm going to try to get better, try to improve on the things I might be struggling with at whatever time it may be," Turner said. "Keep pitching the same way no matter where you're at."