These plants were inoculated with X. campestris pv.
musacearum culture in the midrib of the first fully open leaf. The
control nontransgenic plants started to develop symptoms
(necrosis or chlorosis) at about 14 dpi and died within 38 dpi,
whereas the six transgenic lines remained healthy for 8 weeks,
confirming very high resistance. In these plants, slight browning
was observed at the point of inoculation (Fig. 3E) as a result of
the rapid, localized death of plant cells at the site of inoculation.
This is characteristic of the HR response, which is thought to be
an important defence response to prevent further multiplication
and to restrict the spread of the pathogen to other parts of the
plant (Chen et al., 2000). To confirm this, pathogenic bacteria
were isolated from the pseudostem and inoculated leaves of all
asymptomatic transgenic lines tested. The inability to recover
viable bacteria from even the inoculation sites of the transgenic
plants indicated a successful resistance response. One transgenic
line showed delayed symptoms after 30–35 dpi, indicating
partial resistance. The reduction in wilting was significantly
higher in this line compared with nontransgenic plants. The
bacterial population was restricted to the leaf inoculated in this
line, as bacteria were not recovered from the pseudostem of
these plants.