Abstract
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.
Highlights
Wilt caused by the bacterial pathogen, Ralstonia solanacearum is a serious limiting factor affecting the cultivation of tomato world over [1] [2]
Comparing the 2 - 5-week-old seedlings of Arka Vikas through root-injury inoculation, the younger the seedling, the more was the susceptibility to the pathogen (Figure 1)
By 4 weeks, the extent of mortality in the first three age groups appeared almost similar, but it was relatively less in 5-week-old seedlings with the maximum plant stand (74%, 68%, 63% and 49% mortality, respectively)
Summary
Wilt caused by the bacterial pathogen, Ralstonia solanacearum is a serious limiting factor affecting the cultivation of tomato world over [1] [2]. It is essential to evolve disease management practices to facilitate the growing of wilt-susceptible otherwise superior genotypes. Use of antagonistic microorganisms and soil amelioration are adopted towards this objective [1] [3]-[6]. Tomato being essentially a transplanted crop, injury to roots at field planting is often inevitable. With the practice of growing the seedlings in organic planting medium in protrays, it has been possible to plant them in the field with the intact ball of cocopeat thereby minimizing the chances of root injury
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