2.4. Root dipping
Due to the shortage of pine seedlings, only one fungal isolate
(F668) was used in this experiment. Root dip coatings were prepared
with either Xan (0.2%) or MC (2%) as described above. In total,
four root dip treatments were prepared: 1. F668 Xan, 2. F668
MC, 3. Control Xan (no fungi), 4. Control MC (no fungi).
Batches of 10 surface sterilised P. radiata seeds were placed on
sterile filter paper moistened with sterile distilled water in 55 mm
Petri dishes. Dishes were placed in the dark at 20 C for 2–3 weeks
until the seeds germinated. When the radicle on germinated seeds
was 2–3 cm long, they were inoculated with F668 or the blank
coatings described above. Each radicle was inoculated by holding
seeds in sterilised forceps and dipping the root into the coating
suspension for 10 s, after which the seedlings were placed in a sterile
Petri dish to allow the coating to air-dry. Treated seedlings were
individually planted into 6-Paks containing Garden Grow compost
(South-Hort, NZ) and grown in a greenhouse at approximately
20 C, transplanting into PB bags at 8 weeks old. Seedlings were
watered weekly for the remainder of the trial.
Radicle loadings were determined by placing a coated root into
5 mL of sterile 0.01% Triton X-100 in a sterile 20 mL plastic tube.
Roots were allowed to soak for 10 min to rehydrate the coating,
and tubes were then shaken on a wrist shaker set at maximum
for a further 10 min. Serial dilutions were prepared from the stock
suspension and 100 lL aliquots plated onto BSM. Two repli-plates
were prepared for each dilution. Plates were incubated at 20 C and
cfus counted after 10 days. Radicle loadings for the F668 treatments
were 1.3 107 conidia for the MC treatment and
2.13 106 for the Xan treatment. At 2, 4 and 9 months after germination
five seedlings from each treatment were randomly chosen
and destructively sampled as described below.
2.5