Effect of Two Strains of Plant Growth Promoting Rhizobacteria (PGPR) on the Chlorophyll Content and Virus Concentration in Tomato Plants Infected with Tomato Spotted Wilt Virus Under Protected Cultivation

Abstract

Tomato spotted wilt virus (TSWV) is considered an epidemic disease of solanacious crops, causing severe losses in protected cultivations at different regions of the world. This study was conducted to evaluate the efficiency of two strains of plant growth promoting rhizobacteria, Pseudomonas chlororaphis MA342, and Bacillus subtillis FZB27, in the induction of systemic acquired resistance in tomato plants against TSWV, in greenhouses, by estimating the photosynthetic chlorophyll and virus concentration. The research was carried out on tomato plants grown under protected agriculture, at the Agricultural Research Centre in Lattakia, during the fall and winter of 2019-2020 growing season. The experiment was designed following a randomized complete block design, with 10 treatments and 4 replications of 6 plants for each replicate, making the total number of plants in the experiment, 240 plants. The bacteria was applied by seed treatment, root irrigation and foliage spray. Virus inoculation was carried out by thrips, the common vector of TSWV. The following parameters were estimated: Content of photosynthetic pigments (chlorophyll A, B, and carotenoids), viral concentration, and viral inhibition rate (%), 30 days after virus inoculation. Results obtained showed an increase in the amount of chlorophyll A, in plants inoculated with TSWV and treated with PGPR bacteria (0.349-0.517 mg/g), and this was significantly higher than the control treatment (0.142 mg/g). The amount of chlorophyll B in plants inoculated with TSWV and treated with the bacteria (0.201-0.279 mg/g) was also higher than the control treatment (0.166 mg/g), but the difference was not significant. The application of the bacteria increased the amount of chlorophyll A and B, with highest rate of increase reached 265.49 and 68.07 %, respectively, when the strain B27 was used by the three application methods (seed treatment, root irrigation, and foliage spray). DAS-ELISA readings showed significantly lower concentration of viral antigen in PGPR treated tomato leaves (0.378-0.908), compared with the control treatment (1.202), 30 days after virus inoculation.

Keywords:

TSWV, PGPR, photosynthetic pigments, viral concentration, DAS- ELISA.