CHICAGO -- The Cubs' Minor League hierarchy will look mostly the same in 2021, as baseball alters its player development structure.

On Wednesday, the Cubs announced that they have invited Triple-A Iowa, Double-A Tennessee, Class A (high) South Bend and Class A (low) Myrtle Beach to remain affiliates with the franchise. All four teams have been linked to the Cubs for several seasons, or decades in the case of Iowa.

"We are pleased to invite four of our long-time affiliates to continue working with us and help develop our players," Cubs vice president of player development Matt Dorey said in a statement. "These four teams have combined to work with the Cubs for 66 years, and that is only possible with strong ownership, hardworking front offices and welcoming communities at each level of our system."

The Cubs no longer will field the Eugene Emeralds as an affiliate, though the team was added by the Giants as their new Class A (high) ballclub. In his statement, Dorey thanked the front-office leadership of Eugene for their commitment and efforts, which contributed to Northwest League titles in 2016 and '18.

Iowa has been affiliated with the Cubs since 1981, marking the third-longest run of any Triple-A club with the same MLB franchise. Tennessee has been associated with the Cubs since 2007, while South Bend and Myrtle Beach both joined the team's player-development system in '15.

During the 2020 season, when Minor League Baseball shut down due to the COVID-19 pandemic, the Cubs used the South Bend ballpark and facilities in Indiana as their alternate training site. There, a select group of prospects and big league reserves continued to get work in a controlled, safe environment.

"I was really proud of all the work we did in player development this year," Cubs president of baseball operations Jed Hoyer said recently. "I think South Bend and instructional league was kind of a really good test case for that. The way I see it is this: There's no substitute for playing 140 games in the Minor Leagues. That's obviously the best way to develop players. But, I think in this odd year, I think all improvement was kind of relative.

"If you were improving more, relative to your competition, I think you really gained. And I have no question that we made significant gains over our competition this year, judging by the improvements our guys made at South Bend and the improvements I know guys made on their own in these odd settings.

"I'm super proud of what we did in player development and I'm really excited going forward. I think that we're definitely on the right track with the right people and I'm excited to play a lot of Minor League games in '21 to prove that."