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Bioefficacy evaluation of salicylic acid, and radiation-modified carrageenan and chitosan for inducing tomato leaf curl resistance
Thesis Abstract:
Tomato leaf curl is a major virus disease problem in tomato production. This study was conducted to evaluate the bioefficacy of three chemicals—namely, salicylic acid (SA), and radiation-modified carrageenan and chitosan as inducer of resistance. Specifically, this study determined the optimum concentration of these inducers, and the proper time for inducing tomato resistance to leaf curl infection. Healthy seedlings of susceptible tomato varieties, Apollo White or Marimar, were treated with varying concentrations of each inducer at different induction time, applied before plants were inoculated with the virus. The resistance induced was determined through reduction in disease incidence, the amount of disease produced over time measured as AUDPC value, and of symptom severity. Salicylic acid treatment at low concentration regardless of the induction time reduced the disease incidence and the amount of disease, and reduced the symptom severity. At 1–4 wpi, Apollo White variety with 50 μM SA treatment had significantly lower disease incidence than the untreated control. Treatment with 250 μM and 500 μM had significantly lower incidence only at the early stages of infection (1 and 2 wpi). Plants treated with 50 μM, 250 μM, and 500 μM SA were not significantly different (1199%, 1359.8%, and 1399.9%-days, respectively) but significantly lower than untreated control (1783.3%-days). Plants sprayed with 50 μM SA had significantly lower symptom severity score (0.4) than the untreated (0.94). Chitosan treatment at 50 ppm, 100 ppm, and 250 ppm had reduced disease incidence (16.7%, 16.7%, and 20.4%, respectively) compared to the untreated control (51.6%). Based on AUDPC, plants sprayed with chitosan at 50 ppm had the slowest disease progress (1179.6%-days), followed by 100 ppm (1224.9%-days), 250 ppm (1315.7%-days) than the untreated control (1477.7%-days). Plants treated with 50 ppm, 100 ppm, and 250 ppm carrageenan had significantly lower symptom severity score (0.2, 0.1, and 0.3, respectively) than the untreated (0.6). Apollo White variety treated with 50 ppm carrageenan had significantly lower disease incidence (22.2%, 61.1%, and 81.4%) at 1 wpi, 2 wpi, and 3 wpi, respectively, than the untreated control (79.6%, 96.3%, and 100%) at 1 wpi, 2 wpi, and 3 wpi, respectively. Treatment with 50 ppm had lower AUDPC values (466%-days) than the untreated control (1639.7%- days). Moreover, plants treated with 50 ppm, 150 ppm, and 250 ppm carrageenan had significantly lower symptom severity score (1.3, 1.5, and 1.4, respectively) than the untreated control (1.7) at 2 wpi. The Marimar variety treated with 50 ppm carrageenan also had reduced disease incidence at 1–2 wpi. Plants treated with 50 ppm carrageenan had significantly lower disease incidence (25.9%) than untreated control (79.6%). Based on AUDPC values, plant treated with 50 ppm carrageenan had AUDPC values of 1464.1%-days, which were significantly lower than the untreated control (2464.2% days). Plants treated with 50 ppm had significantly lower symptom severity score (1.4) than untreated control (1.8). The induction time did not show any effect on disease development, and there was no significant interaction between the concentration and induction time.