Dunsby chaired the group in the 1980s, while also heading growing media producer Silvaperl Group, which he founded, until the company was taken over by William Sinclair Horticulture.
Dunsby and his wife Beryl then formed Perlex Associates which administered JIMA and, between 1992 and 1997, the Commercial Horticultural Association. He received the Queen's Award for Achievement in Enterprise Promotion in 2008.
Neil Bragg, chair of the Horticultural Development Company and product development director at JIMA member Bulrush Horticulture, said: "Brian and Beryl raised the profile of John Innes composts and their manufacturers to a highly professional and publicly recognised level, and we all unreservedly thank them for their input over the years."
The administration of JIMA is now being handled by the HTA, alongside the Growing Media Association.