“Partner” (as in “Howdy, Pardner!”) is often written as spoken, as “pardner” or “podner” or “pard.” These spellings are found in print from at least the 1830s.
(Dictionary of American Regional English)
partner n
Forms. Pronc-spp paa’dnuh, pard(e)ner, podna, podner; abbr pard scattered, but chiefly Sth, S Midl, SW
1795 Dearborn Columbian Grammar 137, List of Improprieties...Pardener for Partner. 1837 Sherwood Gaz. GA 71, Pardner, for partner. 1843 in 1940 Chabot TX Letters 46, I am chained now to Milvern Harold who makes a first rate pard.
1 June 1835, American Magazine of Useful and Entertaining Knowledge, “Collection of Vulgarisms; or Yankeeisms,” pg. 416:
Pardner for partner.