Role of Bacillus amyloliquefaciens Y1 in the control of Fusarium wilt disease and growth promotion of tomato

The objective of this study was to examine the effects of Bacillus amyloliquefaciens Y1 on the control of Fusarium wilt disease and subsequent improvement in the growth of tomato plants. The Y1 strain strongly inhibited Fusarium oxysporum f. sp. lycopersici in vitro and also produced indole-3-acetic acid (IAA) in both the presence and absence of tryptophan. Over 96% of tomato seeds germinated when treated with either water, tryptone soy broth, or Y1 cultures, whereas root (5.40?cm) and shoot (5.15?cm) lengths were greatest in tomato seedlings treated with Y1 cultures that lacked tryptophan. Three experimental treatments – Black White medium (BW), BW medium with a commercial fungicide (BW?+?F), and Y1 culture inoculated in BW medium (Y1) – were applied to control Fusarium wilt disease under in vivo conditions. Application of Y1 culture and BW?+?F led to significantly lower disease incidence than did BW; moreover, shoot length and fresh and dry weight of both roots and shoots were greater in plants treated with Y1 than in plants treated with either BW or BW?+?F. A similar trend was observed for chitinase and β-1,3-glucanase activities in roots and leaves of tomato plants in all treatment groups over most of the experimental period. Finally, the presence of Y1 in the rhizospheric soils of Y1-treated plants resulted in a significant reduction in the populations of other bacteria. The results of our study demonstrated the effectiveness of Y1 not only in the control of Fusarium wilt disease but also for the enhancement of plant growth in cultivated tomato.     

<Emphasis Type="Italic">Fusarium sambucinum</Emphasis> isolate FS-94 induces resistance against fusarium wilt of tomato via activation and priming of a salicylic acid-dependent signaling system

The wheat rhizosphere-inhabiting nonpathogenic Fusarium sambucinum isolate FS-94 protected tomato from Fusarium wilt (F. oxysporum f. sp. lycopersici) in laboratory experiments. Seed soaking or immersion of seedling roots in a FS-94 spore suspension prior to inoculation with the pathogen delayed the appearance of wilt symptoms and significantly reduced disease severity in plants of a susceptible tomato cultivar. Quantification of fungal ergosterol in infected tomato showed that protection against wilt agent was related to limitation of the pathogen growth in plants exposed to FS-94. Incubation of tomato seedlings in a FS-94 spore suspension for 48 or 72 h led to plant protection and increased the salicylic acid (SA) concentration in their roots, suggesting that this isolate was involved in a plant-mediated mode of action and induced resistance. Soaking tomato seeds in the spore suspension did not induce SA accumulation in seedling roots, but nevertheless resulted in a significant reduction in wilt severity when the seedlings were challenged with the pathogen. In response to pathogen attack, the SA content in susceptible seedlings grown from FS-94-treated seeds started to increase within 1 day and remained elevated for 72 h. This suggests that F. sambucinum isolate FS-94 primed a SA-dependent signaling system in tomato.     

Effect of root exudates of mycorrhizal tomato plants on microconidia germination of Fusarium oxysporum f. sp. lycopersici

The effect of root exudates from mycorrhizal and non-mycorrhizal tomato plants on microconidia germination of the tomato pathogen Fusarium oxysporum f. sp. lycopersici was tested. Microconidia germination was enhanced in the presence of root exudates from mycorrhizal tomato plants. Tomato plants were colonised by the arbuscular mycorrhizal fungus Glomus fasciculatum, indicating that alterations of the exudation pattern depended on the degree of root AM colonisation. Testing the exudates from plants with a high and a low P level revealed that the alterations of the root exudates from mycorrhizal plants, resulting in a changed effect on microconidia germination, are not due to an improved P status of mycorrhizal plants.     

A comparison of wild-type, old and modern tomato cultivars in the interaction with the arbuscular mycorrhizal fungus Glomus mosseae and the tomato pathogen Fusarium oxysporum f. sp. lycopersici

The effect of the arbuscular mycorrhizal symbiosis (AM) varies in plant cultivars. In the present study, we tested whether wild-type, old and modern tomato cultivars differ in the parameters of the AM interaction. Moreover, the bioprotective effect of AM against the soilborne tomato pathogen Fusarium oxysporum f. sp. lycopersici (Fol) was tested in the different cultivars. Ten tomato cultivars were inoculated with the arbuscular mycorrhizal fungus (AMF) Glomus mosseae alone or in combination with Fol. At the end of the experiment, AM root colonization, Fusarium infection, and the plant fresh weight was determined. The tomato cultivars differed in their susceptibility to AMF and Fol, but these differences were not cultivar age dependent. In all the cultivars affected by Fol, mycorrhization showed a bioprotective effect. Independent of the cultivar age, tomato cultivars differ in their susceptibility to AMF and Fol and the bioprotective effect of mycorrhization, indicating that the cultivar age does not affect the AM parameters tested in this study.     

Root exudates of mycorrhizal tomato plants exhibit a different effect on microconidia germination of Fusarium oxysporum f. sp. lycopersici than root exudates from non-mycorrhizal tomato plants

The effect of root exudates from mycorrhizal and non-mycorrhizal tomato plants on microconidia germination of the tomato pathogen Fusarium oxysporum f. sp. lycopersici was tested. Microconidia germination was enhanced in the presence of root exudates from mycorrhizal tomato plants. The more tomato plants were colonized by the arbuscular mycorrhizal fungus Glomus mosseae, the more microconidia germination was increased, indicating that alterations of the exudation pattern depended on the degree of root AM colonization. Moreover, alterations of the exudation pattern of mycorrhizal plants are not only local, but also systemic. Testing the exudates from plants with a high and a low P level revealed that the alterations of the root exudates from mycorrhizal plants, resulting in a changed effect on microconidia germination, are not due to an improved P status of mycorrhizal plants.     

Arbuscular mycorrhizal fungi and Trichoderma viride mediated Fusarium wilt control in tomato

The biocontrol potential of two arbuscular mycorrhizal fungi (AMF) (Funneliformis mosseae and Acaulospora laevis) and Trichoderma viride was assessed against tomato wilt caused by Fusarium oxysporum Schlecht. f. sp. lycopersici under pot condition. All the bioagent showed appreciable results in increasing plant growth. Combined inoculation of F. mosseae, A. laevis and T. viride showed maximum increases in plant height, shoot fresh weight, root dry weight, number of leaves and number of branches per plant while dual inoculation of F. mosseae and T. viride increased rest of the growth parameters like shoot dry weight, root fresh weight, root length and leaf area. AM colonisation and spore number was found highest in single inoculation of AMF, which decreases with the addition of T. viride. But, this decrease has no effect on biocontrol efficiency of bioagents. Photosynthesis, chlorophyll content and nutrient content were markedly decreased by pathogen infection. Bioagent application overcomes this effect and a remarkable increase in the plant phosphorus and nitrogen content was recorded. Among both the AMF, F. mosseae proved to be more effective strain compared to A. laevis for tomato. Maximum reduction in disease incidence and severity was recorded in combined inoculation of F. mosseae, A. laevis and T. viride. Whereas control plants without any bioagent showed maximum occurrence of disease. The findings of this study concludes that soil inoculation with F. mosseae along with root inoculation with conidial suspension of T. viride before transplantation offered better survival and resistance to tomato seedlings against Fusarium wilt.     

Interactions between a fluorescent pseudomonad,an arbuscular mycorrhizal fungus and a hypovirulent isolate of Rhizoctonia solani affect plant growth and root architecture of tomato plants

Abstract

Although Rhizoctonia solani is a cosmopolitan soilborne pathogen, the genus includes isolates with different pathogenicity ranging from high virulence to avirulence. The biocontrol strain Pseudomonas fluorescens P190r and the arbuscular mycorrhizal (AM) fungus Glomus mosseae BEG12 were inoculated alone or in combination in tomato plants infested by the mildly virulent pathogen R. solani #235. Plant growth as well as root morphometric and topological parameters were evaluated. The infection of R. solani was significantly reduced by all the combinations of the beneficial microorganisms. Root systems of R. solani‐infected plants were weakly developed but highly branched with a herring‐bone pattern, while those inoculated with the AM fungus, alone or in combination with the bacterial strain, were longer and more developed, and displayed a dichotomous pattern. The interactions among these three microorganisms affected plant growth and root architecture of tomato plants.     

The effects of Fusarium oxysporum f.sp. lycopersici (Sacc.) Snyder & Hansen on tomato in diphenamid-treated soil

Pre-emergence soil application of the herbicide diphenamid in concentrations exceeding the normal field rate increased the resistance of tomato plants towards infection by the wilt fungus Fusarium oxysporum f.sp. lycopersici. This was detected as significant increases in the percentage emergence of seedlings although growth parameters of the raised seedlings were reduced. Treated plants exhibited no wilt symptoms, although the pathogen maintained its population at detectable levels in the rhizosphere of tomato plants. However, the growth inhibition caused by diphenamid alone was much less than that reported for the combined application of pathogen and herbicide. Growth activities of F. oxysporum f.sp. lycopersici were inhibited by high concentrations of diphenamid in vitro. It is possible that the biodegradation of this herbicide by species such as Aspergillus candidus (present in substantial counts in treated rhizospheres) was one of the causes of increased tolerence of the pathogen to the herbicide in situ.     

Control of Fusarium wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici using leaf extract of Piper betle L.: a preliminary study

The main objective of this study was to evaluate the effectiveness of crude chloroform extract of Piper betle L. (PbC) in controlling Fusarium wilt of tomato (Lycopersicon esculentum) caused by Fusarium oxysporum f. sp. lycopersici. It was observed that 1% (w/w) amendment of the PbC in soil was more efficient in reducing the Fusarium population in soil than carbendazim and the combined amendment of carbendazim and PbC. Fusarium wilt control studies were carried out in a greenhouse. Variation in different parameters like shoot growth, root growth and mean fresh weights of tomato seedlings in all the treatments were recorded. Accumulation of total phenolics was also studied from the root tissues of tomato. Higher accumulation of total phenolics was observed in the Fusarium-infested plants as compared to that of healthy control and PbC-treated plants. Moreover, it was observed that the extract could reduce the symptoms and disease development. Electron microscopy studies were also done to observe the Fusarium infestation in the vascular bundles and to show the accumulation of total phenolics in the vacuoles of root tissue.     

Biological control of Fusarium wilt of tomato with <Emphasis Type="Italic">Fusarium equiseti</Emphasis> GF191 in both rock wool and soil systems

The plant growth-promoting fungus (PGPF) Fusarium equiseti GF191 was tested for its ability to control Fusarium wilt of tomato (FWT) caused by Fusarium oxysporum f. sp. lycopersici (FOL) in both a hydroponic rock wool and soil system. F. equiseti effectively controlled FWT, with protective effects based on disease severity of 66.7–88.6% in four experiments. The numbers of colony-forming units of FOL per gram fresh weight of stems were significantly reduced (P < 0.05) in plants treated with F. equiseti. Stem extracts from F. equiseti-treated and pathogen-challenged plants significantly inhibited the germination and germ-tube length of FOL microconidia and the production of FOL budding-cells. Tomatine content in tomato stems treated with F. equiseti was significantly increased compared with the non-treated control.     

The membrane mucin Msb2 regulates invasive growth and plant infection in Fusarium oxysporum

Fungal pathogenicity in plants requires a conserved mitogen-activated protein kinase (MAPK) cascade homologous to the yeast filamentous growth pathway. How this signaling cascade is activated during infection remains poorly understood. In the soil-borne vascular wilt fungus Fusarium oxysporum, the orthologous MAPK Fmk1 (Fusarium MAPK1) is essential for root penetration and pathogenicity in tomato (Solanum lycopersicum) plants. Here, we show that Msb2, a highly glycosylated transmembrane protein, is required for surface-induced phosphorylation of Fmk1 and contributes to a subset of Fmk1-regulated functions related to invasive growth and virulence. Mutants lacking Msb2 share characteristic phenotypes with the Δfmk1 mutant, including defects in cellophane invasion, penetration of the root surface, and induction of vascular wilt symptoms in tomato plants. In contrast with Δfmk1, Δmsb2 mutants were hypersensitive to cell wall targeting compounds, a phenotype that was exacerbated in a Δmsb2 Δfmk1 double mutant. These results suggest that the membrane mucin Msb2 promotes invasive growth and plant infection upstream of Fmk1 while contributing to cell integrity through a distinct pathway.     

Interaction between Fusarium oxysporum F. vasinfectum and Cephalosporium maydis on cotton and maize

The interaction between Fusarium oxysporum (cause of cotton wilt) and Cephalosporium maydis (cause of maize late-wilt) on cotton roots is associated with an appreciable decrease in the severity of the cotton wilt disease. Reduction in infection is more pronounced when the latter fungus precedes the former in the soil than when they are inoculated simultaneously. C. maydis exerts little or no such effect when it follows F. oxysporum in the soil. C. maydis grows on the surface of cotton roots near growing points as a root-surface inhabitant. Dark red lesions are produced but these disappear, as does the fungus, when the root becomes hardened either naturally or in response to the growth of the fungus on the surface. The presence of the fungus is associated with increased production of root laterals. Cotton plants, including those which may appear healthy, show only mild internal symptoms of Fusarium infection when grown in soil inoculated with the two fungi, suggesting that the decreased severity of wilt is largely due to increased tolerance of the plants to infection with the disease as a result of increased number of root laterals. It is also possible that cotton roots with C. maydis on their surface become less suitable for the progress of F. oxysporum. F. oxysporum produces in culture a metabolite inhibitory to C. maydis. This may partly account for the little effect that the latter fungus exerts on the severity of wilt when it follows F. oxysporum in the soil. It appears that the interaction between F. oxysporum and C. maydis does not affect the pathogenicity of the latter fungus to maize.     

Salicylic Acid Enhances Resistance to Fusarium oxysporum f. sp. phaseoli in Common Beans (Phaseolus vulgaris L.)

Fusarium wilt caused by Fusarium oxysporum f. sp. phaseoli (Fop) is one of the most serious diseases of common bean (Phaseolus vulgaris L.) and is especially prevalent in China. In this study, we demonstrated that exogenous application of 2 mM salicylic acid (SA) by leaf spraying could induce resistance against Fop in common beans. Accumulation of free and conjugated SA in roots was detected by HPLC analysis and compared. After 168 h of daily SA treatment, the free SA level in roots was eight times higher than in control plants. However, the conjugated SA level reached a peak at 72 h of SA treatment, which was nine times higher than in control plants, and then sharply declined at 168 h. The activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5) and peroxidases (POX, EC 1.11.1.7) in roots were 9.4 and 6.3 times higher than in control plants after 168 h of SA treatment, respectively. H₂O₂ and O₂ ^? levels reached 2.6 and 13.6 times higher, respectively, than in the control plants at 168 h after SA treatment. Host reactions of SA-treated plant roots infected by Fop observed in microscopy included the deposition of electron-dense materials along the secondary walls. However, untreated inoculated plants showed marked cell wall degradation and total cytoplasm disorganization of root cells. These results indicated that SA applied to foliar tissue is capable of enhancing the systemic acquired resistance of common bean roots to infection by Fop.     

Induction of systemic resistance in chickpea against Fusarium wilt by Bacillus strains

Plant growth promoting rhizobacteria (PGPR) strains Rb29 (B. amyloliquefaciens MF352007), Bs1 (B. subtilis MF352017) and Bt1 (B. tequilensis MF352019) were tested for growth promotion and for their ability to induce systemic resistance against Fusarium wilt, a vascular disease of chickpea, using two methods that include whole plant and a split-root system. Bacillus strains and Fusarium oxysporum f. sp. ciceris (FOC) were inoculated on separate halves of roots of chickpea seedlings at the same time and then planted in separate pots either in superposition or one side of the other. All Bacillus strains systemically induced resistance against FOC, and significantly (p < 0.05) reduced the wilt disease by 98–100%. Application of Bacillus strains effectively enhanced plant growth, leading to increased plant height, root length, a fresh and dry weight of shoots and roots. These results help to explain the role of strains of Bacillus in growth promotion and biological control of Fusarium wilt in chickpea. This is the first report of systemic-induced resistance against Fusarium wilt in chickpea obtained by application of Bacillus strains to a root system spatially separated from the FOC-inoculated root.     

Effects of arbuscular mycorrhiza (AM) on health ofLinum usitatissimum L. infected by fungal pathogens

Effects of arbuscular mycorrhizal (AM) symbiosis on health ofLinum usitatissimum infected by fungal pathogens were investigated exemplarily. Physiological and biochemical analyses were done to explain the mechanisms underlying the AM effects. AM plants showed increased resistance against the wilt pathogen (Fusarium oxysporum f. sp.lini), the level of this effects depended on the plant cultivars which all showed the same level of root colonization by arbuscular mycorrhizal fungi (AMF). In contrary to that, AM plants were highly susceptible against the shoot pathogenOidium lini, but they suffered less than non-AM plants in terms of shoot fresh weight, CO₂ assimilation and content of sucrose in shoot apex. This indicates that AM not only activates resistance mechanisms but also can induce tolerance against pathogens. The concentration of phytohormones such as auxin- and gibberellin-like substances were increased in shoots of AM plants. In roots the ethylene production was increased, too. Furthermore the content and composition of free sterols were highly altered in leaves of AM plants. Root infection by AMF caused an increased respiratory activity and a reduced degree of DNA methylation, but both modifications only occurred in infected root parts indicating an increasing gene activity. The presented results suggest that nearly all parts of a plant are influenced by AM but not in the same manner. In the case of mildewed linseed the effect of AM on plant health was impressing, it indicates that AM has an ability to induce tolerance.     

Interactions between the soilborne root pathogenPhytophthora nicotianae var.parasitica and the arbuscular mycorrhizal fungusGlomus mosseae in tomato plants

In order to study the influence of Arbuscular Mycorrhiza (AM) on the development of root rot infection, tomato plants were raised with or withoutGlomus mosseae and/orPhytophthora nicotianae var.parasitica in a sand culture system. All plants were fed with a nutrient solution containing one of two phosphorus (P) levels, 32µM (I P) or 96µM (II P), to test the consequence of enhanced P nutrition by the AM fungus on disease dynamics. Mycorrhizal plants had a similar development to that of control plants. Treatment withPhytophthora nicotianae var.parasitica resulted in a visible reduction in plant weight and in a widespread root necrosis in plants without mycorrhiza. The presence of the AM fungus decreased both weight reduction and root necrosis. The percentage reduction of adventitious root necrosis and of necrotic root apices ranged between 63 and 89% The enhancement of P nutrition increased plant development, but did not appreciably decrease disease spread. In our system, mycorrhiza increased plant resistance toP. nicotianae var.parasitica infection. Although a contribution of P nutrition by mycorrhiza cannot be excluded, other mechanisms appear to play a crucial role.     

Improved growth of salinity-stressed soybean after inoculation with salt pre-treated mycorrhizal fungi

Two sets of experiments to determine the effect of mycorrhiza on soybean (Glycine max) growth under saline conditions and to investigate the salt acclimation of mycorrhizal fungi were conducted. In the first experiment, the effect of an arbuscular mycorrhizal (AM) fungus Glomus etunicatum on mineral nutrient, proline and carbohydrate concentrations and growth of soybean. Under different NaCl concentrations (0, 50, 100, 150 and 200mM) was evaluated. Salinity decreased AM colonization. In both the M and nonAM plants shoot and root proline and shoot Na and Zn concentrations were increased under salinity. Soybean plants inoculated with the AM fungus had significantly higher fresh and dry weight, root proline, P, K and Zn but lower shoot proline and Na concentrations compared to the non inoculated plants. In the second experiment, the AM fungus was pre-treated with NaCl (salt acclimation) then was used as inoculum for soybean plants subjected to 100mM NaCl. Root colonization, fresh and dry weight, root proline, P, K and Zn concentrations were greater in soybean plants inoculated with the salt pre-treated fungus, compared to those inoculated with the nonsalt pre-treated fungus. However, for Na, the situation was the opposite. Based on these results, the AM inoculation helps the growth of soybean plants grown in saline conditions. When the AM fungus was pre-treated with NaCl with a gradual increase of concentration, and then exposed to a sudden salt stress, their efficiency was increased. This may be due to the acclimation of the AM fungus to salinity.     

香蕉植株根区土壤的真菌多样性分析

尖孢镰孢菌古巴专化型(Fusarium oxysporum f.sp.cubense)是香蕉枯萎病的病原菌,该菌是一种土壤习居菌,了解香蕉根区土壤中真菌多样性及镰孢菌属(Fusarium)真菌所占比例,对如何减少土壤中的病原菌、预防香蕉枯萎病的发生有重要的指导意义。该文通过采集不同宿根年限的香蕉健康植株和枯萎病植株的根区土壤,利用高通量测序技术测定土壤样品中的真菌种群。结果表明:(1)同一宿根年限的香蕉植株中,健康植株根区土壤中所获的reads及OTUs数量均高于枯萎病植株,说明健康植株根区土壤的真菌多样性丰富于枯萎病植株。(2)除了一年生香蕉枯萎病植株以担子菌门(Basidiomycota)为主外,其他土壤样品中均以子囊菌门(Ascomycota)为主,其中的丛赤壳科最高相对丰度来自三年生健康植株的根区土壤(26.02%),其次是五年生的枯萎病植株根区土壤(15.56%)。(3)在丛赤壳科中,镰孢菌属在三年生健康植株土壤中的相对丰度最高(2.54%),在其他样品中的相对丰度在0.1%～0.65%之间;在镰孢菌属中,腐皮镰孢菌(Fusarium solani)的相对丰度(0～1.59%之间)高于尖孢镰孢菌(F.oxysporum),尖孢镰孢菌仅占很小的比例(相对丰度0～0.08%之间)。可见,在不同香蕉植株的根区土壤中,健康植株的根区土壤真菌多样性高于枯萎病植株,无论是健康植株还是枯萎病植株的根区土壤中,作为香蕉枯萎病病原菌的镰孢菌属或尖孢镰孢菌的群体均不占主导地位。     

Ralstonia solanacearum colonization of tomato roots infected by Meloidogyne incognita

Bacterial wilt, caused by Ralstonia solanacearum, is one of the most serious diseases of tomato (Solanum lycopersicum). Concomitant infection of R. solanacearum and root‐knot nematode Meloidogyne incognita increases the severity of bacterial wilt in tomato, but the role of this nematode in disease complexes involving bacterial pathogens is not completely elucidated. Although root wounding by root‐knot nematode infection seems to play an important role, it might not entirely explain the increased susceptibility of plants to R. solanacearum. In the present study, green fluorescent protein (GFP)‐labelled R. solanacearum distribution was observed in the root systems of the tomato cultivar Momotaro preinoculated with root‐knot nematode or mock‐inoculated with tap water. Fluorescence microscopy revealed that GFP‐labelled R. solanacearum mainly colonized root‐knot nematode galls, and little or no green fluorescence was observed in nematode‐uninfected roots. These results suggest that the gall induced by the nematode is a suitable location for the growth of R. solanacearum. Thus, it is crucial to control both R. solanacearum and root‐knot nematode in tomato production fields to reduce bacterial wilt disease incidence and effects.