Genetic diversity of the bacterial wilt pathogen Ralstonia solanacearum using a RAPD marker

Management of bacterial wilt (Ralstonia solanacearum) of brinjal using Bacillus cereus, Trichoderma harzianum and Calotropis gigantea consortia in Bangladesh

Background

Bacterial wilt caused by Ralstonia solanacearum is a devastating disease of brinjal in Bangladesh. The study was targeted to evaluate the bacterial wilt management ability of microbial consortia composed of isolated and identified native Bacillus cereus, Trichoderma harzianum and Calotropis gigantea for the first time in Bangladesh.

Results

Twenty bacterial strains were isolated from the rhizosphere of the brinjal plant following serial dilution method. Among the strains, HSTUB 17 showed maximum zone of inhibition (1.5 ± 0.1 cm) against R. solanacearum in the dual culture method. Molecular characterization using 16 s rRNA partial coding sequence revealed HSTUB 17 as B. cereus. Consortia composed with the identified B. cereus HSTUB 17 (108 CFU ml−1 @ 5 ml/plant), previously isolated T. harzianum (@5 mm size of four mycelial disk/plant) and aqueous leaf extracts of C. gigantea (1:1, w/v basis @ 40 ml/plant) were applied in the root zone following soil drenching method and found to reduce bacterial wilt incidence by 74.87, 66.67 and 66.67% at 30, 50 and 70 days after transplanting, respectively, in comparison with plants received only R. solanacearum (108 CFU ml−1 @ 5 ml/plant). The single application of B. cereus HSTUB 17, T. harzianum and C. gigantea also minimized wilt incidence by 21.16–37.34, 33.33 and 21.48–28.14%, respectively, on all the days of observations. The consortia of B. cereus HSTUB 17, T. harzianum and C. gigantea also resulted in maximum plant height (56.67 cm), the number of branches/plants (10.33), the number of fruits/plants (8.33) and fruit yield (25.56 ton/ha) in comparison with the plant exposed to R. solanacearum only.

Conclusion

The findings of the study revealed the potentiality of consortia composed of B. cereus HSTUB 17, T. harzianum and C. gigantea for the eco-friendly management of bacterial wilt of brinjal for the first time in Bangladesh.

Rep-PCR Analyses Reveal Genetic Variation of Ralstonia solanacearum Causing Wilt of Solanaceaous Vegetables in Bangladesh

Ralstonia solanacearum, a soil-borne and seed-borne plant pathogenic bacterium, causes bacterial wilt to several important crop plants causing substantial economic losses. To provide population information on this pathogen for developing effective control strategies, Rep-PCR was used to analyze the genetic variation of 18 representative isolates of R. solanacearum collected in Bangladesh. Phenotypic analyses revealed that all eighteen isolates belong to biotype 3 with wide diversity in aggressiveness on eggplant, tomato, and chili. Rep-PCR studies utilizing the REP, ERIC, and BOXIR primers showed a wide variation at the genetic level among the R. solanacearum isolates used in this study. Dendrogram constructed using REP, ERIC, and BOXIR primers based on banding patterns implied that R. solanacearum isolates were genetically diversified and distributed in four clusters at 83%, 80%, and 63% similarity index, respectively. The genetic relationship assayed by rep-PCR highlighted a wide range of genetic variation but no relation among geographical origin, aggressiveness, and phylogenetic groups of R. solanacearum isolates. These results conceded that other molecular markers related to virulence gene(s) might reveal the complex relationship among geographical origin, aggressiveness, and phylogenetic groups.

Eco-friendly application of nano-chitosan for controlling potato and tomato bacterial wilt

Bacterial wilt is one of the main diseases of Solanum spp., which caused by Ralstonia solanacearum (RS), formerly known as Pseudomonas solanacearum. Different concentrations of chitosan nanoparticles have been evaluated as one of the alternative methods of disease management in vitro and in vivo to reduce the risks of pesticide residues. Results in vitro experiment indicated that RS5 isolate was the most virulence one compared to RS1 and RS3. Increasing concentration of nano-chitosan, lead to increase inhibition zone, and this was observed at higher concentrations (100 and 200 µg/ml). In vivo results showed the highest concentration of spraying chitosan nanoparticles increase percentage reduction of disease incidence and severity, in effected potato and tomato plants. Recorded data of disease incidence and severity in treated potato plants were 78.93% and 71.85%, while on tomato plants were 81.64% and 77.63%, respectively compared to untreated infected potato plants were recorded 15.38%, 20.87%, and tomato plants were 20.98% and 28.64%. Results also revealed that 100 µg/ml of chitosan nanoparticles the lowest treatments used as soil amended curative treatments led to incease percentage reduction of disease incidence and severity, respectively on potato and tomato plants, but less than preventive treatment. The results registered that on potato plant were 54.93% and 52.65%, whilst recorded on tomato plants were 59.93% and 56.74%. Transmission electron microscopy (TEM) micrpgraphs illustrated that morphological of healthy R. solanacearum cells were undesirably stained with uranyl. The electron-dense uranyl acetate dye was limited to the cell surface slightly than the cytoplasm, which designated the integrity of the cell film of healthy cells. While bacterial cells treated with nano-chitosan, showed modification in the external shape, such as lysis of the cell wall and loss of cell flagella. Also, the result of using Random amplified polymorphic DNA (RAPD)-PCR observed that differences in treated Ralstonia solanancearum genotype by nano-chitosan compared to the genotype of the same untreated isolate.