Mechanisms Involved In The Biological Control Of Tomato Bacterial Wilt Caused By Ralstonia Solanacearum Using Arbuscular Mycorrhizal Fungi

Glasshouse experiment was done to study the ability of two local mycorrhizal fungi species (Glomus mosseae, Scutellospora sp.,) and introduced species (Gigaspora margarita) to colonize and enhance some tomato growth parameters. G. mosseae showed the best preformance among species used. G. mosseae was able to increase significantly plant height (60% ), shoot dry weight (135%) and flowers number (58%) compared to the control plant at the 7th weeks of plant growth. G. mosseae alter root structures such as root dry weight (42%), root tips (120%), root length(83%), root surface area (106%), and root volume (59%), which can increase nutrient absorption and enhance plant growth. G. mosseae was adapted to the local environmental conditions which resulted in more root colonization (300%) and more spores number (300%), different from the introduced species G. margarita. The overall data presented in this study showed that local species can be used for enhancing yield growth more than the introduced species. Three mechanisms were described to explain by how arbuscular mycorrhizal fungi (AMF) inhibit or control the bacterial wilt disease. Nutrient uptake, biochemical changes and root morphological changes were the mechanisms studied. The concentrations of N (41%), P (133%), K (49%), Fe (44%), and Zn (33%) in tomato shoots were increased after the colonization of G. mosseae, indicating that AMF was able to increase the shoot nutrient uptake due to the hyphal net were produced by AMF which allow the roots to absorb more nutrient. The root morphological characteristics (root dry weight, root tips, root volumes, root length and root surface area) were changed significantly in G. mosseae treatment compared to all other treatments. The SEM and TEM images provided evidence that AMF can modify the root cortex cells and root structure which finally helps the plant to prevent the disease infection totally. The G. mosseae hyphal structures were seen inside the cortex cell. Disease symptoms were not seen in the G. mosseae +R. solanacearum treated plants. The extensive colonization by AMF was the reason behind the high concentration of chlorophyll (a) and chlorophyll (b) which could contribute to the increase of photosynthetic rate in tomato leaves and enhance plant growth. Ch.(a) and ch.(b) in G. mosseae treated plants was significantly higher compared to the rest of the treatments. G. mosseae can be used as a bio-protection agent because it can provide root with hyphal net which can minimize the bacterial wilt infection. The production of healthy, huge number and clean G. mosseae spores were the targets of another glasshouse experiment. The results obtained from this experiment showed that the harvest date and the type of the crops were played a critical role in AMF spore production. Corn was the most suitable host for G. mosseae sporulation (167 spore/10gm soil). Lentil, green bean, and barley showed low AMF sporulation and colonization related to the inability of these crops to grow under glasshouse conditions. Several important factors must be considered in AMF mass production, included plant host species, environmental conditions, soil types, nutrient regime, pot size, inoculum amount and the source of primary inoculum. In vitro experiments were done to study the effects of different root exudates with and without pre-inoculation with G. mosseae on the control of R. solanacearum and to study the indirect interaction between G. mosseae and R. solanacearum. In general, the influence of root exudates produced from tomato and corn plants on G. mosseae spore germination showed different response. The spores germination number was decreased using different volumes of mycorrhizal tomato root exudates (MTRE) and mycorrhizal corn root exudates (MCRE). It was increased when non-mycorrhizal tomato root exudates (NMTRE) and non-mycorrhizal corn root exudates (NMCRE) were applied in different volumes. G. mosseae spores germinated in all types of media used. The spore germination number was increased by increasing the original number of spores cultured and this indicated that the volatiles compounds produced from bacterial pathogen did not inhibit the spore's germination. The overall results concluded from these studies confirm that the local species of AMF were more able to support and enhance plant growth compared to the introduced species. G. mosseae was able to control totally the bacterial wilt causal agent R. solanacearum under glasshouse conditions. Nutrient uptake, biochemical changes and root morphological changes were the three mechanism tested. The production of huge number of AMF spores is a critical area for mycorrhizal research using suitable host plant as a trap

Ralstonia solanacearum: the bacterial wilt causal agent

Ralstonia solanacearum (race 3 biovar 2) is a bacterial wilt causal agent of many plant species. Infects (potatoes Solanum tuberosum, eggplant Solanum melongena, peppers Capsicum annuum, tomatoes Lycopersicon esculentum, geraniums, Geranium carolinianum, ginger Zingiber officinale and a few weed species including bittersweet Celastrus orbiculatus, nightshade Solanum karsense and stinging nettle Urtica dioica. Ralstonia solanacearum can be infectious in the soil for years in the presence of a host. Race 3 biovar 2 is most commonly transmitted by contaminated soil, equipment, water and insect, or by transplantation of infected seeds or seedlings. Management requires use of resistance cultivars, clean and certified seed, good cultural practices, some chemicals fumigation, antagonistic microbes as a biological control like (Mycorrhizal fungi, Streptomyces sp. and Tricoderma sp.) transgenic resistant plant, cropping systems, soil amendments, integrated control, genetically engineered antagonistic and virulent mutants of R. solanacearum

The potential of endomycorrhizal fungi in controlling tomato bacterial wilt Ralstonia solanacearum under glasshouse conditions

The impact of colonization by three mycorrhizal fungi on tomato bacterial wilt caused by Ralstonia solanaceraum was investigated. Three species of arbuscular mycorrhizal fungal (AMF) were tested (Glomus mosseae, Scutellospora sp. and Gigaspora margarita). Siginificant differences in tomato growth based on plant hieght was recorded between G. mosseae (125.25 cm) and all treatments. The combination of G. mosseae and R. solanacearum resulted in significantly taller tomato plants than G. margarita + R. solanacearum and Scutelospora sp.+ R. solanacearum. Shoot fresh and dry weight was higher in G. mosseae inoculated plants. No disease symptoms were observed in the combination treatment of G. mosseae and R. solanacearum. The plants treated with Scutellospora sp. showed low incidence of infection (105, 15%) at 15 and 20 days after inoculation, respectively. The combination of G. mosseae and R. solanacearum resulted in more increase in root morphology (root tips (434.75), root length (267.00 cm), root surface area (149.31 cm2), root volume (3.77 cm3), root fresh weight (4.75 g) and root dry weight (2.5 g). The treatment of G. mosseae + R. solanacearum was different significantly when compared to G. margarita and Scutellospora sp. + R. solanacearum treatments in all parameters considered. The highest number of AMF spores was recorded in G. mosseae treatment followed by Scutellospora sp. The concentration of N, P and K in G. mosseae + R. solanacearum treatment was significantly higher (N: 1.69; P: 0.51 and K: 1.65%) compared to G. margarita (N: 1.06 ; P: 0.11 and K: 1.02%) and Scutellospora sp., treatment (N: 1.48; P: 0.44 and K: 1.47%). Generally, the current findings has provided an evedance about the ability of AMF species to control bacterial wilt causal agents with significant differences between the species used.Keywords: Bio-control, wilt disease, tomato, Glomus mossea

Bio-compartmental in vitro system for Glomus mosseae and Ralstonia solanacearum interaction.

The life cycle of arbuscular mycorrhizal fungi (AMF) is initiated by spore germination. The interaction between Glomus mosseae and Ralstonia solanacearum was achieved by following the bio-compartmental in vitro system. The system was modified to be useful for different microbes with different types of medium. Mycorrhizal fungi spores were germinated using water agar, nutrient agar and soil media, while casamino acid-peptone-glucose (CPG) media was used for R. solanacearum.all medium. All medium were mixed with different volumes of tomato and corn root exudates. The hyphal length of G. mosseae greatly affected by the exudates particularly, mycorrhizal tomato root exudates (MTRE) and mycorrhizal corn root exudates (MCRE). The growth of R. solanacearum was suppressed due to G. mosseae spores germination which can produce different volatile and non volatiles substances. The aim of this experiment was to investigate the influence of root exudates volatiles on R. solanacearum and the hyphal of G. mosseae growth under laboratory conditions using a new modified technique

Role of plant host in determining differential responses to Ralstonia solanacearum and Glomus mosseae

A pot study was aimed to investigate the role of tomato in determining differential response to bacterial wilt causal agent Ralstonia solanacearum pathogen and arbuscular mycorrhizal fungi (AMF) Glomus mosseae. Disease severity was measured after 10, 20 and 30 days of plant growth. The pathogen and dual treatment (R. solanacearum with G. mosseae) were not significantly different at the end of this experiment. Soil pH was greatly influencing the pathogen and AMF microbe. Glomus mosseae mycorrhizosphere was more alkaline (pH 5.9) compared to the pathogen mycorrhizosphere (pH 4.9). The concentration of bacterial cell in the R. solancearum soil was not different from the dual treatment after 60 days of plant growth. Spore germination was influenced by the interaction between the soil pathogen and AMF. Spores number in the dual treatment at 60 days was less than the original number added. Root colonization percentage in G. mosseae (61%) was significantly more than the dual treatment (16%). This provide an evidence about the role of plant host in increasing the spores germination influenced by many substances produced by the host root (root exudates). The results demonstrated that the role of plant in determination the relationship between soil-borne pathogen and antagonistic microbe was critical