Last season's runners-up St Mirren take on Lowland League champions East Kilbride, while Highland League winners Buckie Thistle host Brechin City.
Morton are up against Livingston, Queen of the South welcome Airdrieonians, Dunfermline meet Arbroath and East Fife are paired with Peterhead.
Colt teams from all 12 Premiership clubs are involved at this stage.
Falkirk and Inverness Caledonian Thistle enter in the second round, along with Crusaders and Linfield from Northern Ireland, Welsh duo Gap Connah's Quay and The New Saints and Bray Wanderers and Sligo Rovers from the League of Ireland.
The first round ties will be played on the weekend of 15/16 August.
North Section
Aberdeen U20 v St Johnstone U20
Buckie Thistle v Brechin City
Dundee U20 v Alloa Athletic
Dundee United v Cowdenbeath
Dunfermline Athletic v Arbroath
East Fife v Peterhead
Formartine United v Hearts U20
Hibernian U20 v Elgin City
Raith Rovers v Brora Rangers
Ross County U20 v Forfar Athletic
Stenhousemuir v Cove Rangers
Stirling Albion v Montrose
South Section
Albion Rovers v Spartans
Annan Athletic v Celtic U20
Clyde v Stranraer
Dumbarton v Rangers U20
East Stirlingshire v Ayr United
Greenock Morton v Livingston
Hamilton Accies U20 v Edinburgh City
Kilmarnock U20 v Berwick Rangers
Motherwell U20 v Queen's Park
Partick Thistle U20 v Stirling University
Queen of the South v Airdrieonians
St Mirren v East Kilbride
Holders Dundee United are at home to Cowdenbeath in the first round of the Irn Bru Challenge Cup.