Molecular Identification and Evaluation of Indigenous Bacterial Isolates for Their Plant Growth Promoting and Biological Control Activities against Fusarium Wilt Pathogen of Tomato

Abstract

In search of an effective biological control agent against the tomato pathogen Fusarium oxysporum f. sp. lycopersici, rhizospheric soil samples were collected from eight agro-ecological zones of Bangladesh. Among the bacteria isolated from soil, 24 isolates were randomly selected and evaluated for their antagonistic activity against F. oxysporum f. sp. lycopersici. The two promising antagonistic isolates were identified as Brevundimonas olei and Bacillus methylotrophicus based on morphological, biochemical and molecular characteristics. These two isolates were evaluated for their biocontrol activity and growth promotion of two tomato cultivars (cv. Pusa Rubi and Ratan) for two consecutive years. Treatment of Pusa Rubi and Ratan seeds with B. olei prior to inoculation of pathogen caused 44.99% and 41.91% disease inhibition respectively compared to the untreated but pathogen-inoculated control plants. However, treatment of Pusa Rubi and Ratan seeds with B. methylotrophicus caused 24.99% and 39.20% disease inhibition respectively. Furthermore, both the isolates enhanced the growth of tomato plants. The study revealed that these indigenous bacterial isolates can be used as an effective biocontrol agent against Fusarium wilt of tomato.

Keywords: Fusarium oxysporum; biological control; fusarium wilt; plant growth promoting rhizobacteria; tomato.

Fig. 1

Inhibition of F. oxysporum f. sp. lycopersici by two bacterial isolates (A) Bacillus methylotrophicus Prb1, and (B) Brevundimonas olei Prd2, and (C) mycelial growth of F. oxysporum in control plate.

Fig. 2

Phylogenetic tree showing position of the biocontrol agents (▲) used in this study. The 16S rDNA sequences were aligned with the ClustalW and the tree was constructed with the maximum likelihood method based on the Tamura-Nei model integrated in the MEGA7 software. The GenBank accession numbers of the DNA sequences are shown in parentheses.

Fig. 3

The effect of bacterization of tomato seeds with two biocontrol agents on shoot length of tomato seedlings. Data are mean of three replications. Bars indicate standard error of the mean.

Fig. 4

The effect of bacterization of tomato seeds with two biocontrol agents on root length of tomato seedlings. Data are mean of three replications. Bars indicate error of the mean.

Fig. 5

The effect of bacterization of tomato seeds with two biocontrol agents on the fresh weight of tomato seedlings. Data are mean of three replications. Bars indicate standard error of the mean.

Fig. 6

The effect of bacterization of tomato seeds with two biocontrol agents on vigor index of tomato seedlings. Data are mean of three replications. Bars indicate standard error of the mean.