The study was undertaken to assess whether seedling age played any role in governing the vulnerability of tomato to the bacterial wilt pathogen, Ralstonia solanacearum, based on the preliminary observations that the extent of mortality during seedling-stage screening was relatively less in older seedlings. Employing the virulent strain ‘NH-Av01’ isolated from tomato, 2-, 3-, 4- or 5-week-old seedlings of susceptible ‘Arka Vikas’ raised in organic cocopeat in 98 cavity protrays were inoculated with the pathogen through root-injury inoculation approach. Disease symptoms appeared earlier and with more severity in 2-week-old seedlings followed by 3-, 4- and 5-week-old saplings recording 74%, 68%, 63% and 49% mortality, respectively, after four weeks of inoculation suggesting that older the seedlings, less the susceptibility to the pathogen. The growth characteristics of seedlings (shoot height, shoot and root weights) showed a significant increase with seedling age (0.21, 0.54, 1.14 and 2.09 g gross weight/seedling at 2, 3, 4 and 5 weeks, respectively) indicating healthier saplings with delay in inoculation time. In subsequent trials, seedlings of 3, 4, 5 or 6 weeks were transplanted to field-sick soil in protrays or in pots with monitoring for 1 - 4 months which indicated a significant reduction in disease incidence and severity with increase in seedling age. The observations suggested that seedling age should be considered as a major factor influencing the susceptibility of tomato seedlings to R. solanacearum with the chances of variations in the extent of disease incidence or inconsistent results during seedling-stage screening and the possibility of escapes with older seedlings. Two-week seedlings formed the best when the aim is to induce maximum disease incidence, while transplanting at 5 - 6 weeks stage appeared the best when the objective is minimal disease incidence or formulating disease management strategies.
The study was taken up with the
objective of testing whether the endophytic organisms isolated from crops that
are normally non-hosts to the bacterial wilt pathogen Ralstonia solanacearum possessed pathogen-antagonistic activity and
to evaluate the selected isolates for the alleviation of wilt disease in the
target tomato crop through horizontal movement of promising organisms. Sixteen
endophytic bacteria (EB) isolated from the micropropagated cultures of grape,
watermelon and papaya were tested for potential antagonistic effects against R. solanacearum tomato isolate “NH-01”
through agar-well diffusion assay. Enterobacter
cloacae from papaya (EB-11) displayed the maximum antagonistic effect
followed by Bacillus subtilis (EB-06)
and B. flexus (EB-07) from watermelon
and B. pumilus (EB-02) from grape.
Testing the above organisms for crop protection through seed fortification of
susceptible tomato cv. Arka Vikas at sowing in R. solanacearum inoculated (Ral+) organic cocopeat showed EB-02 and EB-11
promising (33% and 32% survival, respectively, four weeks after sowing against
15% in Ral+ control). A second trial
showed 37%, 28%, 21% and 55% seedling survival 6 weeks after sowing for EB-02,
EB-06, EB-07 and EB-11 respectively, compared to 2.5% in non-treated control.
Assessing the four endophytes for crop protection in