2.1. Isolation of endophytic fungi
Healthy plants of oilseed rape (B. napus) were collected in two
growing seasons (Nov. 2008 to May 2009 and Nov. 2009 to May
2010) grown in fields in Wuhan city, Hubei Province of central
China (30280N, 114210E). At each of the four growth stages (seedling, bolting, flowering and podding) in each season, five healthy
plants were carefully up-rooted using a spade, individually placed
in plastic bags and immediately taken to laboratory. The plants
were washed in tap water to remove soil particles on the roots
and the basal stems. Young leaves, the main stems and the taproots
were detached from each plant for fungal isolation.
The sampled leaves were cut into 3-cm squares, three leaves per
plant at each growth stage. The main stems and the taproots were
cut into 3-cm-long segments. The leaf pieces and the segments of
stems and roots were surface sterilized following the procedures
described by Hallmann et al. (2006), briefly in 70% ethanol (v/v)
for 1 min, then in 5% sodium hypochlorite (v/v) for 5 min, again
in a 70% ethanol for 30 s, and finally rinsed in sterile water 3 times
(3 min each). The surface-disinfected plant tissues were blotted
dry on sterilized filter paper. The ends of each stem and root segment were cut off using a sterile razor blade and the remaining
part of each segment was transversely cut to 2-mm-thick slices,
which were individually placed in Petri dishes (9 cm in diameter)
containing acidified potato dextrose agar (PDA), five slices per dish
and two dishes per plant. For the leaf samples, the margins of each
leaf piece were cut off and the central part was cut into 0.5-cm
squares, and placed on acidified PDA in Petri dishes, five pieces
per dish and two dishes for each leaf sample. The dishes with plant
tissues were incubated at 20 C and examined daily for fungal
growth for up to 4 weeks. The fungal colonies were individually
transferred to new PDA dishes, one colony per dish, and incubated
at 20 C. The resulting fungal cultures were purified by singlespore- or single-hypha-tip isolation. Finally, the pure cultures were
stored in 20% glycerol (v/v) at 80 C.