Wilt Severity Research Articles

The endophytic strain Bacillus velezensis OEE1: An efficient biocontrol agent against Verticillium wilt of olive and a potential plant growth promoting bacteria

The use of antagonists in the biocontrol of soilborne pathogens is a promising approach to manage many diseases. In this context, Bacillus velezensis strain OEE1, isolated from endogenous root tissue of olive trees, showed the most effective antifungal activity under in vitro conditions against V. dahliae with inhibition rate exceeding 92% using the dual culture method to investigate effects of diffusible compounds. This antagonism was also demonstrated with volatile and extracellular compounds where fungus growth was reduced by about 40% and 60% respectively. Gnotobiotic study of axenic in vitro olive plants, artificially inoculated with V. dahliae, using B. velezensis OEE1 cells led to a considerable reduction in Verticillium wilt severity and the disease index effectively decreased for preventive and curative treatments. Vegetative growth showed equally an interesting improvement. These potentialities are provided due to the production of numerous secondary metabolites detected by antibiotic biosynthesis genes amplification. The efficacy of B. velezensis OEE1 to suppress Verticillium wilt of olive tree was evaluated also under field conditions. This experiment revealed that B. velezensis OEE1 significantly decreased final mean disease severity index (FMS), percentage of dead plants (PDP) and area under disease progress curve (AUDPC) and reduced similarly microsclerotia density in the naturally infested soil.

Cultivar-Dependent Variation of the Cotton Rhizosphere and Endosphere Microbiome Under Field Conditions.

Verticillium wilt caused by Verticillium dahliae is a common soil-borne disease worldwide, affecting many economically important crop species. Soil microbes can influence plant disease development. We investigated rhizosphere and endosphere microbiomes in relation to cotton cultivars with differential susceptibility to Verticillium wilt. Soil samples from nine cotton cultivars were assessed for the density of V. dahliae microsclerotia; plants were assessed for disease development. We used amplicon sequencing to profile both bacterial and fungal communities. Unlike wilt severity, wilt inoculum density did not differ significantly among resistant and susceptible cultivars. Overall, there were no significant association of alpha diversity indices with wilt susceptibility. In contrast, there were clear differences in the overall rhizosphere and endosphere microbial communities, particularly bacteria, between resistant and susceptible cultivars. Many rhizosphere and endosphere microbial groups differed in their relative abundance between resistant and susceptible cultivars. These operational taxonomic units included several well-known taxonomy groups containing beneficial microbes, such as Bacillales, Pseudomonadales, Rhizobiales, and Trichoderma, which were higher in their relative abundance in resistant cultivars. Greenhouse studies with sterilized soil supported that beneficial microbes in the rhizosphere contribute to reduced wilt development. These findings suggested that specific rhizosphere and endosphere microbes may contribute to cotton resistance to V. dahliae.

Biochar Suppresses Bacterial Wilt of Tomato by Improving Soil Chemical Properties and Shifting Soil Microbial Community.

The role of biochar amendments in enhancing plant disease resistance has been well documented, but its mechanism is not yet fully understood. In the present study, 2% biochar made from wheat straw was added to the soil of tomato infected by Ralstonia solanacearum to explore the interrelation among biochar, tomato bacterial wilt resistance, soil chemical properties, and soil microbial community and to decipher the disease suppression mechanisms from a soil microbial perspective. Biochar application significantly reduced the disease severity of bacterial wilt, increased soil total organic carbon, total nitrogen, C:N ratio, organic matter, available P, available K, pH, and electrical conductivity. Biochar treatment also increased soil acid phosphatase activity under the non-R.-solanacearum-inoculated condition. High-throughput sequencing of 16S rRNA revealed substantial differences in rhizosphere bacterial community structures between biochar-amended and nonamended treatments. Biochar did not influence soil microbial richness and diversity but significantly increased the relative abundance of Bacteroidetes and Proteobacteria in soil at the phylum level under R. solanacearum inoculation. Furthermore, biochar amendment harbored a higher abundance of Chitinophaga, Flavitalea, Adhaeribacter, Pontibacter, Pedobacter, and Ohtaekwangia at the genus level of Bacteroides and Pseudomonas at the genus level of Proteobacteria under R. solanacearum inoculation. Our findings suggest that a biochar-shifted soil bacterial community structure can favorably contribute to the resistance of tomato plants against bacterial wilt.

Biological control of Fusarium wilt on watermelon by fluorescent pseudomonads

ABSTRACTFusarium wilt caused by Fusarium oxysporum f. sp. niveum (FON) is a destructive soilborne disease commonly found in watermelon producing areas throughout the world. At present, the control of Fusarium wilt depends heavily on host resistance and chemical fungicide application. In this study, we isolated fluorescent pseudomonads from the rhizosphere of healthy watermelon and evaluated their biocontrol capacity against FON race 2. Biochemical assays indicated that all 14 fluorescent Pseudomonas strains were able to produce indole-3-acetic acid and at least one type of biosurfactants. Both sulphur oxidising and proteolytic activities were exhibited in 2 of the 14 strains. However, none of them could synthesise phenazine antibiotics. Seven strains with different morphological and biochemical characteristics were identified by sequencing the rpoB gene. Among those, one was Pseudomonas resinovorans (WMT16-1-1), two were P. putida (WMC16-1-1 and WMC16-2-5), one was P. fluorescens (WMC16-1-8) and others were Pseudomonas sp. In vitro studies indicated that WMC16-1-1, WMC16-1-8 and WMC16-2-5 inhibited mycelial growth of FON significantly. Detection of biosynthetic loci of 2,4-diacetylphloroglucinol (DAPG), pyrrolnitrin and pyoluteorin using specific primers indicated that the three strains could not produce the antibiotics. In greenhouse studies, WMC16-1-1, WMC16-1-8 and WMC16-2-5 reduced the severity of Fusarium wilt significantly with WMC16-1-1 being the most effective. Inoculation with WMC16-2-5 resulted in the significantly greater weight of both stems and roots compared to the nontreated control, while WMC16-1-1 resulted in greater stem weight. Pseudomonas strains WMC16-1-1, WMC16-1-8 and WMC16-2-5 are potential candidates for controlling Fusarium wilt and promoting the growth of watermelon.

First Report of Root Rot and Wilt Caused by Pythium myriotylum on Hemp (Cannabis sativa) in the United States

In September 2018, a hemp plant (Cannabis sativa L. cv. Dinamed) presented severe wilting, root rot, and mortality in a research greenhouse at the University of Connecticut in Storrs, CT. The hemp plant was grown in a 11.36-liter container with soilless peat-based potting mix (SunGro Fafard 3B, Agawam, MA, U.S.A.). The plants were in a polycarbonate greenhouse with a daytime heating set point of 20°C and a ventilation set point of 26°C under 18 h of supplemental lighting. Roots were collected from the symptomatic hemp plant, washed three times with sterile deionized water, blotted dry, and plated on PARP selective medium (Jeffers and Martin 1986). The plates were incubated in the dark at 21°C for 48 h. Mycelia resembling the morphology of Pythium species were observed in all plates. Following van der Plaats-Niterink’s key (van der Plaats-Niterink 1981), the isolate was identified as Pythium myriotylum based on the morphology of sexual and asexual structures. Colonies grown on sterile tall fescue leaves had filamentous, inflated, nonproliferating sporangia that ranged in width between 6 and 16 μm. Oogonia were 28 to 30 μm in diameter, globose, and had a smooth, thick wall (1 to 2 µm). The antheridia were curved, bulbous, and developed on branched stalks with multiple antheridia per oogonium. The appressoria were clavate, and oospores were mostly aplerotic. DNA was extracted from mycelial mats using the DNeasy Plant Mini Kit (Qiagen, Germantown, MD, U.S.A.). The cytochrome oxidase subunits I and II (coxI and coxII) (Martin 2000; Robideau et al. 2011) and the internal transcribed spacer (ITS) regions 1 and 4 (White et al. 1990) were amplified. The amplicons were sequenced and BLAST analyzed in NCBI GenBank. The isolate was confirmed to be P. myriotylum with ≥98% query coverage and 100% identity match to GenBank accession numbers LC440564.1, KJ595365.1, and KX671106. The nucleotide sequences obtained in this project have been assigned the GenBank accession numbers MN037880, MN037881, and MN022496 for coxI, coxII, and ITS, respectively. To confirm Koch’s postulates, three 68-day-old hemp plants (cv. Wife) were inoculated with P. myriotylum with 1 × 10⁵ oospores/ml obtained from three mycelial mats per pot. The mycelial mats, grown in V8 broth, were blended with 500 ml of deionized water, oospores were quantified using a hemocytometer, and the inoculum was applied directly in the potting medium so that no leaching occurred. The hemp plants were grown in 11.36-liter containers in a growth chamber set at 24°C with 65% humidity under 16 h of light. After 20 days, two of the three inoculated plants were wilted, and the control plants were symptomless. Necrotic roots were collected from all the plants. Ten root fragments were plated on PARP selective medium (replicated four times, one plate per replicate). The mycelial growth emanating from roots resembled Pythium on isolation plates from the symptomatic plants, and no growth was observed from roots of noninoculated plants or the asymptomatic plant. Colonies isolated from the root tissue morphologically resembled the originally isolated organism, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of P. myriotylum being detected on a hemp plant in the United States.

Biocontrol Potential of Fungal Endophytes against Fusarium oxysporum f. sp. cucumerinum Causing Wilt in Cucumber.

Endophytic fungi have received much attention as plant growth promoters as well as biological control agents against many plant pathogens. In this study, 30 endophytic fungal species, isolated from various plants in China, were evaluated using in vitro dual culture assay against Fusarium oxysporum f. sp. cucumerinum, causing wilt in cucumber. The results of the present study clearly showed that all the 30 endophytic fungal isolates were highly capable of inhibiting the mycelial colony growth of Fusarium oxysporum f. sp. cucumerinum with inhibition % over 66% as compared to control treatments. Among all of them, 5 isolates were highly effective such as, Penicillium sp., Guignardia mangiferae, Hypocrea sp., Neurospora sp., Eupenicillium javanicum, and Lasiodiplodia theobromae, respectively. The Penicillium sp. and Hypocrea sp. were highly effective as compared to other isolates. From in vitro results 10 best isolates were selected for greenhouse studies. The results of the greenhouse studies showed that among all of them 3 endophytic fungal isolates successfully suppressed wilt severity when co-inoculation with pathogen Fusarium. oxysporum f. sp. cucumerinum. The endophytic fungi also enhanced plant growth parameters of the host plants, the antagonistic fungal isolates increased over all plant height, aerial fresh, and dry weight as compared to control.

Effect of temperature on severity of Fusarium wilt of cabbage caused by Fusarium oxysporum f. sp. conglutinans

The effect of temperature on severity of Fusarium wilt of cabbage caused by pathogen Fusarium oxysporum f. sp. conglutinans was assessed. The pathogen was first tested in vitro for growth under different temperatures of 15, 18, 24, 28 and 37 °C. Based on the results, several temperature variants were selected to test the effect of temperature on the infection of plants grown in substrate. Two susceptible and one resistant variety were chosen for the testing. Cabbage plants were cultivated at temperatures of 16/18 °C, 19/21 °C, 22/24 °C and 26/28 °C. Susceptible varieties showed more severe symptoms and greater plant die-off at higher temperatures (22/24 °C and 26/28 °C), compared to lower temperatures (16/18 °C and 19/21 °C). For the resistant variety, the highest incidence of wilt symptoms was observed at 26/28 °C, while the degree of infection was the same as in susceptible plants at lower temperatures. PCR analysis demonstrated that plants grown at lower temperatures with minimum symptoms were also infected with the pathogen. The study suggested losses due to Fusarium wilt could be reduced by cultivating cabbages during colder periods.

Role of soil physicochemical and microbiological properties in the occurrence and severity of chickpea's Fusarium wilt disease

The aim of the present study is to evaluate the relative disease severity of chickpea wilt in the most important chickpea growing areas in North Algeria and their relationship to soils properties. The physicochemical and biological parameters of 14 soils were analyzed and correlated to the disease index severity ( Dis ). Soil physicochemical factors were determined as a means of particle size distribution, pH, Electrical Conductivity (EC), CaCO 3 content, total Nitrogen (Total-N), Olsen-P and biological factors including Foc inoculum density (ID-Foc), Trichoderma spp propagule number ( TrPn ), Pseudomonas spp and Bacillus spp. The results revealed that the spread of the disease was evident in all prospected areas and recorded as low to medium with values ranging from 2.05 to3 9.8. The disease severity was positively correlated with EC ( r =0.62), Total-N ( r = 0.79), and ID - Foc ( r =0.72), whereas negatively correlated with Olsen-P ( r =-0.67), TrPn ( r =-0.70) and Pseudomonas spp ( r =-0.89). There was no correlation between Dis and soil physical (clay, loam and sand), chemical (pH, CaCO 3 content) and biological factors ( Bacillus spp). As well, ID-Foc was positively correlated with Total-N and negatively correlated with Olsen-P. The results indicated that TrPn and Pseudomonas spp were positively correlated, whereas both were negatively associated with ID-Foc and D is . Our finding pointed out the critical role of some physicochemical and biological soil characteristics in the epidemic development of chickpea wilt under field conditions.

First Report of Fusarium oxysporum Causing Fusarium Wilt on Blueberry (Vaccinium corymbosum) in Chile

Chile is the main exporter of blueberries in the Southern Hemisphere, producing this fruit from October to April each year, when there is no production available in the main markets situated in the northern hemisphere. In Chile, approximately 15,600 ha is planted with highbush blueberries throughout the country. Blueberries are affected by crown and root rot diseases, which reduce productivity (Larach et al. 2009). In 2014, blueberry (Vaccinium corymbosum L. ‘Jolene’) plants showed unusual, severe wilt symptoms (incidence ranging from 50 to 90%), including leaf burn around the margins and brown discoloration of plant crowns, in two orchards of Araucania Region (38°54′00″S, 72°40′00″W) in southern Chile. A fungal species was consistently isolated by cutting small pieces of symptomatic crowns, sterilizing with 1% sodium hypochlorite (1 min), and placing them on potato dextrose agar (PDA). Plates were incubated at 25°C for 7 days. To obtain pure fungal cultures, hyphal tips were transferred to PDA. Upon isolation, colonies formed on PDA developed hyaline aerial mycelium with hints of purple after 7 days. The fungus formed abundant macroconidia and microconidia. The macroconidia were hyaline, slightly sickle-shaped with a foot-shaped basal cell, three to five septations, and 30.34 to 50.67 μm long by 3.22 to 4.58 μm wide. Microconidia were hyaline, oval-ellipsoid to cylindrical, single-celled, and 5.47 to 13.07 μm long by 2.25 to 3.72 μm wide (n = 50). Based on cultural and morphological characteristics, the microorganism was identified as Fusarium oxysporum Schltdl (Leslie and Summerell 2006). For confirmation, DNA was extracted from four isolates, and the ITS region, 18s small subunit rRNA (18s ssu rRNA), and translation elongation factor 1-alpha (tef1-α) genes were amplified with primers ITS1/ITS4, NS1/NS4, and EF1/EF2, respectively, and sequenced. BLAST analysis of the amplified fragments showed that the four isolates were identified as F. oxysporum showing similarity with sequences for ITS (100% identity with accession no. KU986798.1 affecting V. corymbosum; isolates GenBank accession nos. MK356956, MK356957, MK356958, and MK356959), 18s ssu rRNA (99.4% identity with accession no. KP027007.1 affecting Acacia hindsii; isolates GenBank accession nos. MK355436, MK355437, MK355438, and MK35439), and tef1-α (99% identity with accession no. KM092478.1 affecting Vaccinium sp. and 99.4% identity with accession no. MG356947.1 affecting Passiflora edulis; isolates GenBank accession nos. MK414771, MK414772, MK414773, and MK414774) available in the GenBank for this pathogen. To test Koch’s postulates, the crown section of blueberry plants cultivar Jolene (n = 10) was inoculated with 200 µl of 1 × 10⁶ conidia/ml suspension on a 10-mm wound made with a scalpel on the crown base. Inoculated plants were placed in a greenhouse at room temperature (20 to 25°C) for 30 days. After 2 weeks, all inoculated plants produced the same symptoms observed in the field. No symptoms were observed on the negative control plants, which only were inoculated with 200 µl of sterile distillate water (n = 2). Small pieces (3 × 3 mm) of tissue from lesion margins were cultured on PDA. Fungi emerging from tissue pieces were identified based on morphology as F. oxysporum. The experiment was conducted once with the four genetically identified isolates (two replicates per isolate). Although Fusarium wilt of blueberry is reported in China (Liu et al. 2014), to our knowledge, this is the first report of Fusarium wilt on blueberry caused by F. oxysporum in Chile, and this pathogen should be considered among the possible crown and root rot pathogens affecting this important berry crop in the country.

CaWRKY27 negatively regulates salt and osmotic stress responses in pepper

WRKY transcription factors are key regulatory components of plant responses to both biotic and abiotic stresses. In pepper (Capsicum annuum), CaWRKY27 positively regulates resistance to the pathogenic bacterium Ralstonia solanacearum and negatively regulates thermotolerance. Here, we report that CaWRKY27 functions in the response to salinity and osmotic stress. CaWRKY27 transcription was induced by salinity, osmotic, and abscisic acid (ABA) treatments, as determined using qPCR and GUS assays. Transgenic Arabidopsis thaliana and tobacco (Nicotiana tabacum) plants heterologously expressing CaWRKY27 had an increased sensitivity to salinity and osmotic stress, with a higher inhibition of both root elongation and whole plant growth, more severe chlorosis and wilting, lower germination rates, and an enhanced germination sensitivity to ABA than the corresponding wild-type plants. Furthermore, most marker genes associated with reactive oxygen species (ROS) detoxification and polyamine and ABA biosynthesis, as well as stress-responsive genes NtDREB3, were downregulated in plants transgenically expressing CaWRKY27 upon exposure to salinity or osmotic stress. Consistently, silencing of CaWRKY27 using virus-induced gene silencing conferred tolerance to salinity and osmotic stress in pepper plants. These findings suggest that CaWRKY27 acts as a molecular link in the antagonistic crosstalk regulating the expression of defense-related genes in the responses to both abiotic and biotic stresses by acting either as a transcriptional activator or repressor in pepper.

EFFECT OF DIFFERENT INDUCERS ON CONTROLLING DAMPING-OFF AND WILT DISEASES OF LUPINE

The present investigation was carried out to study the effect of seed treatments of lupine plants (cv.Giza 2) with chemical inducers Bion (5mM) , salicylic acid (5mM) and saccharin (3mM) as well as as well as Paenibacillus polymyxa and Trichoderma harzianum as biotic inducers on the infection with Rhizoctonia solani and Fusarium oxysporum f. sp. lupine under greenhouse and field conditions. Under greenhouse condition (Agricultural Research Centre, Giza) all treatments significantly reduced the percentages of pre- and post-emergence damping-off compared with the untreated control, the highest percentage of survived plants was achieved 92% by Bion and T. harzianum as well as fungicide Rizolex-T followed by salicylic acid and P. polymyxa as 88%. On the other hand, all treatments decrease significantly the incidence and severity of wilt, also increased the percentage of survived plants compared with untreated control. Under field conditions at Giza and Ismailia Agricultural Research Stations (Giza and Ismailia governorates) during winter season 2016-2017, all the treatments decreased the percentage of pre- and post-emergence damping-off as well as the percentage of wilted plants and increased the percentage of survived plants compared with untreated control in two locations. At Giza research station, the highest percentages of survived plants were recorded with Rizolex-T followed by Bion, P. polymyxa, and salicylic acid. While at Ismailia, the highest percentage of survived plants were recorded with Rizolex-T followed by Bion, P. polymyxa, T. harzianum, and salicylic acid. Meantime, these treatments improved growth parameters i.e. plant height, number of pods/plant, the weight of seeds /plant and the weight of one hundred seed. The higher increase in seed yield (ton /feddan) was obtained with Rizolex-T and Bion treatments followed by Salicylic acid, P. polymyxa, and T. harzianum at two locations. Activities of peroxidase (PO), polyphenol oxidase (PPO) enzymes and phenol content were determined. Bion treatment showed the highest increase in PO and PPO activity, and total phenols followed by salicylic acid and P. polymyxa treatments in the presence of R. solani or F. oxysporum. f. sp. lupine.

Effect of iodine biofortification on incidence and severity of Fusarium wilt and yield of tomato (<i>Solanum lycopersicum</i> L.)

Tomato is often attacked by wilt caused by Fusarium oxysporium . Iodine is known to have fungistatic effect in pathogen control. The present experiment was aimed at determining the effect of iodine compounds (potassium iodide, KI and potassium iodate, KIO 3 ) on incidence and severity of Fusarium wilt and yield of two tomato accessions, FUNAABTO/106 and FUNAABTO/123. The experiment was conducted in the screenhouse and on the field. KI was applied at concentrations of 1, 2, 3, 5 mM while KIO 3 was applied at concentrations of 0.5, 1, 2, 3 mM. The untreated plots served as control. Results showed that FUNAABTO/106 treated with 0.5 mM KIO 3 in the screenhouse and on the field had the least (0.00%) disease incidence. Disease severity was significantly (p ≤ 0.05) lower (1.00) in the screenhouse in pots containing FUNAABTO/106 treated with 1 mM KIO 3 . On the field, FUNAABTO/106 treated with 0.5 mM KIO 3 had the least (1.17) disease severity. FUNAABTO/106 treated with 0.5 mM KIO 3 in the screenhouse and on the field were significantly higher (1.65t/ha and 18.54t/ha respectively) in yield. The study concluded that application of iodine compounds at lower concentrations reduced the incidence and severity of Fusarium wilt and increased the yield of tomato. Keywords: Potassium iodate (KIO 3 ), Potassium iodide (KI), Fusarium oxysporium

Knockout of SlMAPK3 enhances tolerance to heat stress involving ROS homeostasis in tomato plants

BackgroundHigh temperature is a major environmental stress that limits plant growth and agriculture productivity. Mitogen-activated protein kinases (MAPKs) are highly conserved serine and threonine protein kinases that participate in response to diverse environmental stresses in plants. A total of 16 putative SlMAPK genes are identified in tomato, and SlMAPK3 is one of the most extensively studied SlMAPKs. However, the role of SlMAPK3 in response to heat stress is not clearly understood in tomato plants. In this study, we performed functional analysis of SlMAPK3 for its possible role in response to heat stress.ResultsqRT-PCR analyses revealed that SlMAPK3 relative expression was depressed by heat stress. Here, wild-type (WT) tomato plants and CRISPR/Cas9-mediated slmapk3 mutant lines (L8 and L13) were used to investigate the function of SlMAPK3 in response to heat stress. Compared with WT plants, slmapk3 mutants exhibited less severe wilting and less membrane damage, showed lower reactive oxygen species (ROS) contents, and presented higher both activities and transcript levels of antioxidant enzymes, as well as elevated expressions of genes encoding heat stress transcription factors (HSFs) and heat shock proteins (HSPs).ConclusionsCRISPR/Cas9-mediated slmapk3 mutants exhibited more tolerance to heat stress than WT plants, suggesting that SlMAPK3 was a negative regulator of thermotolerance. Moreover, antioxidant enzymes and HSPs/HSFs genes expression were involved in SlMAPK3-mediated heat stress response in tomato plants.

Genetic control of tomato resistance to Ralstonia solanacearum

Ralstonia solanacearum is one of the causal agent of bacterial wilt in Brazil. This is the main bacteriosis in tomato plants, which can cause losses of up to 100% in their production. The use of resistant cultivars is the main form of control. Thus, the study of genetic control of resistance provides essential information for the conduct of breeding programs. The objective of this work was to study the genetic control of tomato plant ‘Yoshimatsu’ resistance to R. solanacearum. The experiments were conducted in greehouse with the Yoshimatsu and IPA-7 parents; F1, F2, RC11, RC21 generations; and F2:3 progenies. All plants were inoculated using a R. solanacearum isolate from the collection of the Phitobacteriology Laboratory of the Federal Rural University of Pernambuco. The severity of bacterial wilt were assessed through a descriptive scale of scores at 10 and 20 days after inoculation. The resistance to R. solanacearum in the ‘Yoshimatsu’ cultivar is associated with recessive alleles, in which the genetic control of resistance is determined by two independent genes of greater effect with only additive effects, plus polygenes associated with additive and dominance effects.

Field suppression of Fusarium wilt and microbial population Shifts in tomato rhizosphere following soil treatment with two selected endophytic bacteria

Two endophytic bacteria, Bacillus subtilis SV41 (KR818071) and B. amyloliquefaciens subsp. plantarum SV65 (KR818073), were assessed under field conditions for their capacity to control tomato Fusarium wilt in tomato and their effects on soil microbial activity. Six months after planting, Fusarium wilt severity, estimated through the vascular browning extent in tomato stems, was significantly reduced by 82.3 and 88.2% compared to control following bacterial treatments. The frequency of F.oxysporum re-isolation from roots, collars and stems was also significantly lowered in treated plants compared to controls. These effects were associated with a significant improvement, by 10.6 to 16.3%over control, in plant height and root fresh weight and an increase in fruit production by 8.4-12.5%. As for microbial activity, F. oxysporum population in the rhizosphere of tomato plants treated with B. subtilis SV41 and B. amyloliquefaciens subsp. plantarum SV65 was reduced by 87.5-91.7%compared to the initial soil (sampled before planting) and by 88.4-92.3% relative to the rhizospheric soil of untreated plants (control soil). A significant enhancement in the total culturable bacterial community was also noted in the rhizosphere of tomato plants treated with both strains compared to initial and control soils where a significant enrichment in Pseudomonas and actinobacteria community was recorded.

Preliminary Screening of Isolated Mycoherbicidal Fungi for the Management of Noxious Weed Xanthiumstrumarium

Natural phytotoxins of fungi are great source for the discovery of new herbicide and its offer a benign and eco-friendly alternative to manage weed. Thus, this study aimed to select potential fungi with potent herbicidal activity for control ofweeds. In the present study, various phytopathogenic fungi were isolated from infected tissues of various weeds and evaluated againstXanthium strumarium, a problematic monocotyledonous weed of open lands, agriculture, horticulture and forests. Herbicidal potential of Cell Free Culture Filtrate (CFCF) of strains ofPhoma herbarum (FGCCW#18, FGCCW#43) Fusariummonilifromecoded as FGCCW#35 and Fusarium roseum coded as FGCCW#55againstXanthium strumariumwere evaluated by seedling and shoot cut bioassays. Maximum mortalities of shoots, seedlings and phytotoxic damage were obtainedfrom28 day sold cell free culture filtrate (CFCF) of FGCCW#18 at 100% concentration. Significant reduction in biological contents i.e. photosynthetic pigment and protein was observed in the host weed on treatment with the CFCF as determined by detached leaf bioassay. Phytotoxic damage such as severe wilting, chlorosis, necrosis and complete collapse of the entire parts of the weed were also noticed due to CFCF application.

Image-based quantification of Fusarium wilt severity in banana

The severity of Fusarium wilt of bananas has long been classified based on visual assessment of necrosis in rhizome or pseudostem cross-sections. The improved method proposed here uses digital image analysis to quantify the proportion of rhizome tissue that is necrotic. It agrees well with visual classification, but provides greater reproducibility, precision and statistical power.

Effect of Planting Date and Inoculum Density on Severity of Fusarium Wilt of Lettuce in California.

Seven lettuce cultivars were transplanted into a field infested with Fusarium oxysporum f. sp. lactucae (causal agent of Fusarium wilt of lettuce) in August and September of 2014, 2015, and 2016. For moderately susceptible cultivars, 1- or 2-week differences in planting date had a significant effect on severity of Fusarium wilt. In growth chamber experiments, cultivars of moderate susceptibility were maintained in a growth chamber under cool conditions (23/18°C), and a subset of plants was transferred to a warm chamber (33/23°C) for 1 week, at weekly intervals after transplanting. Plants exposed to high temperatures at 2 and 3 weeks after transplanting (WAT) had more severe symptoms of Fusarium wilt than those exposed at 4 WAT. In October 2015, April 2016, August 2016, and August 2017, moderately susceptible cultivars were planted into field soil with an inoculum density gradient. Moderately susceptible cultivars were little affected by Fusarium wilt where inoculum densities of F. oxysporum f. sp. lactucae were <125 per gram of soil, even in warm planting windows. Adjusting planting dates to avoid high temperatures during a critical stage of growth and maintaining low inoculum density in soil can contribute to management of Fusarium wilt in moderately susceptible lettuce cultivars.

The Protective Effect of Trichoderma asperellum on Tomato Plants against Fusarium oxysporum and Botrytis cinerea Diseases Involves Inhibition of Reactive Oxygen Species Production.

Trichoderma species are fungi widely employed as plant-growth-promoting agents and for biological control. Several commercial and laboratory-made solid formulations for mass production of Trichoderma have been reported. In this study, we evaluated a solid kaolin-based formulation to promote the absortion/retention of Trichoderma asperellum in the substrate for growing tomato plants. The unique implementation of this solid formulation resulted in an increased growth of the tomato plants, both in roots and shoots after 40 days of its application. Plants were challenged with two fungal pathogens, Fusarium oxysporum and Botrytis cinerea, and pretreatment with T. asperellum resulted in less severe wilting and stunting symptoms than non-treated plants. Treatment with T. asperellum formulation inhibited Reactive Oxygen Species (ROS) production in response to the pathogens in comparison to plants that were only challenged with both pathogens. These results suggest that decrease in ROS levels contribute to the protective effects exerted by T. asperellum in tomato.

Ralstonia solanacearum colonization of tomato roots infected by Meloidogyne incognita

AbstractBacterial 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.