I just had Agricraft regenerate its mutations file, and the entry for AgriCraft:seedTarmaRoot references seedDesertNova instead of AgriCraft:seedDesertNova:

AgriCraft:seedTarmaRoot=seedDesertNova+AgriCraft:seedShroomBrown

This results in no mutation recipe for Tarma Root. If I add the missing AgriCraft prefix, it works as expected. Here's the versions from my mod mix that have AgriCraft seeds:

Minecraft 1.7.10
AgriCraft 1.4.5
Ars Magica 2 1.4.0.008
Botania 237
Forestry 4.2.0.47
Immersive Engineering 0.6.2
Mekanism (base and generators; no tools) 8.1.7.252
Railcraft 9.8.0.0
Tinker's Construct 1.8.8
Thermal Foundation 1.2.0-102