Abstract To determine what effect fungi and other soil microorganisms have on the root-regenerating potential, seedlings of Pinus radiata were grown in fumigated and nonfumigated nursery beds. Root-regenerating potential was determined by a system of destructive sampling. Beginning in October, when the seedlings were 6 months old and at monthly intervals thereafter until the following August, seedlings were lifted from fumigated and nonfumigated beds, root-pruned, and replanted. After one month's growth the seedlings were carefully examined and all roots which had elongated 0.5 inch or more during the month in the greenhouse were counted. The root-regenerating potential (RRP0.5) was assessed and displayed a seasonal trend essentially similar to that previously reported for ponderosa pine and Douglas-fir. When the seedlings were from fumigated nursery beds the RRP0.5 was significantly higher throughout all but the summer months. Circumstantial evidence suggests that Pythium spp. was responsible for the reduced RRP0.5 of seedlings grown in the nonfumigated nursery beds.
Krugman et al. (Mon,) studied this question.