3. Results
3.1. Bacterial growth
The bacterial colonies on TTC and YDA agar and individual cells
showed the typical R. solanacearum morphology after 48e72 h of
incubation at 28 C. Mucoid colonies grown in the TTC medium
appeared to be white with pink-reddish centers. The mucoid
colonies grown on the YDA medium were creamy-white, opaque
and fluid. After inoculation in tobacco leaves, both colony types
were virulent.
All R. solanacearum isolates caused wilt symptoms and plant
death in the inoculation tests. The first sign of wilt appeared 15 days
after inoculation and plant death occurred about 40 days after
inoculation.
3.2. Thermal treatments
The disease incidences of plants grown in both bagged and not
bagged of pots at 25 C are shown in Table 1. The maximum level of
infection was reached when pots were analyzed directly without
incubation at 25 C (control treatment). The analysis of variance for
disease incidence at 25 C showed that the duration (weeks) of
thermal treatment was a significant factor (P < 0.05).
R. solanacearum was not detected in any of the analyzed plants
after all treatments at 45 C and there was no disease incidence for
all four replications.