An little snatch from a previous search.
"As for jo, it is less clear where it's techniques are derived from. It is known that O-Sensei studied the yari, or
spear of Hozoin Ryu, which bears some resemblance to Aiki-jo, and it is also known that the Kashima and
Katori Shinto Ryus, traditional Schools with a long history in Japan, contain a composite of such weapon arts
as bokken (sword), naginata (halberd), yari (spear) and jo (staff), though how much O-Sensei was influenced
by these is difficult to say. He also studied jukendo (bayonetted rifle) while in the army in the early 1900's,
and certain disarming techniques bear resemblance to some of the jo-dori (staff disarming). O-Sensei did
study, however, an obscure art known as Kuki Shin Ryu, the mystical art of the Yamabushi, or mountain
warriors. The Kumano mountain region near Osaka is famous for such mountain ascetics, and O-Sensei at
one stage of his life retreated there a number of times during the mid-1920's. The preferred weapon of the
Yamabushi is the jo, and according to Stevens, Kuki Shin had considerable influence on Aiki-jo. Kuki Shin
Ryu is also one of the nine traditions of Togakure Ryu Ninjutsu, and a photo of the 33rd Grandmaster of
Togakure Ryu, the late Toshitsugu Takamatsu Sensei, shows him holding a jo in a pose not unlike that of
Aiki-jo. A number of jo-dori within the Togakure Ryu also bear strong resemblance to Aikido jo-dori, though
again, more research is needed to verify this."
You can read the whole thing if you wish.
http://www.aikidoaus.com.au/dojo/docs/weaphist.htm
Of course
I welcome any comments.