Rich 16-6 Trifoliate

Rich 16-6 is a trifoliate orange rootstock selection held by the UCR Citrus Variety Collection as CRC 3485. UCR records that budwood was received from the South Coast Field Station at Irvine in 1965. UCR lists unknown parents and does not identify the original selector or selection date.^⁠[1]

UC Cooperative Extension groups Rich 16-6 with foothill-adapted, semi-dwarfing, cold-hardy rootstocks. In a Georgia comparison using Tango scions, Rich 16-6 was among the rootstocks with the most canopy removed after the Christmas 2022 freeze. Seven of nine Rich trees had been replaced because they were initially smaller; the two older unreplaced trees sustained significant cold damage. These reports do not establish a general temperature limit.^{⁠[12]⁠[5]}

In a Lindcove planting of Frost nucellar navel on Rich 16-6, samples from 1982–84 showed no early tongue formation, though limited shoulder development was reported at Terra Bella. Bitters reports later, unpublished checks that found budunion creasing on Rich 16-6. Together these observations do not establish immunity from decline.^⁠[4]⁠[6]

In a 2016–17 protected nursery study in Punjab, Rich 16-6 seedlings took more than 390 days to reach buddable size, and Kinnow bud take was 46.4%. A related 2019 nursery report overlaps the program; these publications are not independent replications.^{⁠[14]⁠[16]}