Root Rot and Wilt of Kangaroo Paw (Anigozanthos manglesii) Caused by Pythium myriotylum (Drechs.) in Israel

A root rot and wilt disease of Anigozanthos manglesii (Kangaroo Paw) grown in greenhouses in Israel, for exporting as cut flowers to Europe, was characterized. Pythium myriotylum (Drechs.) and Rhizoctonia solani (Kühn) were the prevalent pathogens in diseased plants collected from commercial greenhouses. Fusarium oxysporum, Fusarium spp. and Myrothecium sp. were also isolated, but P. myriotylum or R. solani were not detected in samples from symptomless plants in tissue cultures (Australian origin) or plants at different stages in the nursery; non‐pathogenic F. oxysporum and Fusarium spp. were detected in several samples. In pathogenicity tests carried out in pots, plant mortality occurred 7 days after inoculation with P. myriotylum. In a field experiment carried out in methyl bromide‐fumigated soil, the incidence of dead plants following inoculation with P. myriotylum alone was 22% 10 days after inoculation, increasing to 78% after an additional 25 days. The incidence of dead plants following inoculation with R. solani alone was only 5% and in plants inoculated simultaneously with both pathogens, disease incidence was 88% 35 days after inoculation. Mortality reached 90–100% in plants inoculated with P. myriotylum, either singly or combined with R. solani 60 days after inoculation, whereas in plants inoculated with R. solani it was 5%. The maximum mortality in plants inoculated with R. solani was 25%, 76 days after inoculation. These results clearly demonstrate that P. myriotylum was the dominant pathogen in the root rot and wilt of A. manglesii.     

Microbial conversion and in vitro and in vivo antifungal assessment of bioconverted docosahexaenoic acid (bDHA) used against agricultural plant pathogenic fungi

Microbial modification of polyunsaturated fatty acids can often lead to special changes in their structure and in biological potential. Therefore, the aim of this study was to develop potential antifungal agents through the microbial conversion of docosahexaenoic acid (DHA). Bioconverted oil extract of docosahexaenoic acid (bDHA), obtained from the microbial conversion of docosahexaenoic acid (DHA) by Pseudomonas aeruginosa PR3, was assessed for its in vitro and in vivo antifungal potential. Mycelial growth inhibition of test plant pathogens, such as Botrytis cinerea, Colletotrichum capsici, Fusarium oxysporum, Fusarium solani, Phytophthora capsici, Rhizoctonia solani and Sclerotinia sclerotiorum, was measured in vitro. bDHA (5 μl disc⁻¹) inhibited 55.30–65.90% fungal mycelium radial growth of all the tested plant pathogens. Minimum inhibitory concentrations (MICs) of bDHA against the tested plant pathogens were found in the range of 125–500 μg ml⁻¹. Also, bDHA had a strong detrimental effect on spore germination for all the tested plant pathogens. Further, three plant pathogenic fungi, namely C. capsici, F. oxysporum and P. capsici, were subjected to an in vivo antifungal screening. bDHA at higher concentrations revealed a promising antifungal effect in vivo as compared to the positive control oligochitosan. Furthermore, elaborative study of GC-MS analysis was conducted on bioconverted oil extract of DHA to identify the transformation products present in bDHA. The results of this study indicate that the oil extract of bDHA has potential value of industrial significance to control plant pathogenic fungi.     

Evaluation of antifungal potential of Marchantia polymorpha L., Dryopteris filix-mas (L.) Schott and Ephedra foliata Boiss. against phyto fungal pathogens

Methanol and flavonoid extracts (free and bound) of Marchantia polymorpha L., Dryopteris filix-mas (L.) Schott and Ephedra foliata Boiss. were screened against three fungal plant pathogens: Alternaria solani, Fusarium oxysporum and Rhizoctonia solani. The extracts from D. filix-mas and E. foliata showed >80% of mycelial inhibition of A. solani whereas M. polymorpha and D. filix-mas (rhizome) completely inhibited the mycelial growth of R. solani when tested at highest concentration (5 mg/ml). Inhibition of spore germination of fungi (A. solani and F. oxysporum) was observed to be 100% by most of the extracts at 10 mg/ml. Moreover, plant extracts were found effective in increasing seed germination and seed vigour simultaneously thereby decreasing the percentage of pathogen infection. The results of the present study reveal that the plants screened possess the potential to inhibit the crop fungal pathogens and further investigation is required to explore the biologically active constituents of these plants and to use them as natural plant protectants for agriculture.     

Studies on interaction of Meloidogyne incognita (Kofoid and White) Chitwood and Fusarium solani (Mart.) Sacc forming a disease complex in lentil (Lens culinaris Medik.)

Abstract

An experiment was conducted to study the effects of interaction between Meloidogyne incognita and Fusarium solani on plant length, fresh and dry weights, number of pods, chlorophyll, carotenoid, nitrogen and phosphorus contents and nitrate reductase activity in lentil plants. The results reveal a maximum damage occurring in all the plant growth, biochemical and nutrient parameters, in plants inoculated with M. incognita 10 days prior to F. solani (Mi?→?Fs). This was followed by simultaneous (Mi?+?Fs) inoculations, fungus inoculation 10 days prior to nematode (Fs?→?Mi), M. incognita alone and F. solani alone treatments. Nematode reproduction factor and root galling were highest in individual inoculation of M. incognita, while root rotting percentage was highest when nematode was inoculated 10 days prior to fungus followed by simultaneous inoculation with both nematode and fungus.     

Evaluation of Pseudomonas aeruginosa Z5 for biocontrol of cotton seedling disease caused by Fusarium oxysporum

Plant growth-promoting bacteria-mediated biocontrol of plant pathogens is renowned to enhance the growth of the plants using different direct or indirect mechanisms. The goal of the present investigation was the evaluation of Pseudomonas aeruginosa Z5 isolated from cotton grown in Pakistani soils for the suppression of Fusarium oxysporum associated with cotton seedling disease. In dual culturing techniques, four bacterial strains inhibited fungal pathogens, i.e. F. oxysporum, Fusarium moniliforme, Fusarium solani and Rhizoctonia solani, significantly with percent inhibition ranging from 25% to 91.5%. P. aeruginosa Z5 showed maximum suppression of all the tested pathogens. Net-house experiments showed that the application of P. aeruginosa Z5 both separately and in combination with Bacillus fusiformis S10 significantly reduced the disease incidence by suppressing F. oxysporum (the causal agent of cotton seedling disease) up to 64–65% and improved the percent germination as compared to the infected control plants. The production of antibiotics, proteases and siderophores may be the contributing factors for its antagonistic properties. Highest bacterial population (8.9 CFU/g root) observed on roots of cotton plants inoculated with P. aeruginosa Z5 showed its good colonisation aptitudes even in the presence of high inoculation of soil with F. oxysporum. Confocal laser scanning microscopy supported the root colonisation of cotton plants with fluorescently labelled P. aeruginosa Z5. Because of innate fungicidal potential, growth promoting P. aeruginosa Z5 can be used as a bioinoculant and an antagonist to suppress the growth of cotton root-associated fungal pathogen.     

Etiology of a Root Rot Disease Complex of Alstroemeria in Alberta, Canada

Fusarium oxysporum, Pythiu-m ultimum, and Rhizoctonia solani were isolated from the basal stems of diseased alstroemeria showing symptoms of dark brown stripes along leaf margins, leaf chlorosis, plant wilting, browning or rotting of basal stem, rhizome, and storage and fibrous roots. The pathogen isolated most frequently was Fusarium spp. (40.5 % of plants examined). Pythium spp. and R. solani were isolated less frequently (5.5 % and 6.8 % of plants examined, respectively). F. oxysporum caused the highest mortality in alstroemeria when rhizomes were grown in unsterilized soil-less mix medium. This is the first report in North America of a root-rot disease complex affecting alstroemeria.     

Diversity of Fusarium Species Isolated from Weeds and Plant Debris in Croatia

Weeds are alternative hosts of plant pathogens and when colonized may not exhibit disease symptoms. In 2008 and 2009, samples of weeds and plant debris were collected from 12 locations in eastern Croatia, and 300 Fusarium isolates colonizing them were identified. Strains were grouped and identified based on morphology and amplified fragment length polymorphism (AFLP) patterns. Portions of the β‐tubulin and translocation elongation factor 1‐α genes were sequenced from representative strains of each group to confirm the identifications. Fourteen Fusarium species were identified with F. graminearum (20%), F. verticillioides (18%), F. oxysporum (16%), F. subglutinans (13%) and F. proliferatum (11%) all present as more than 10% of the population. Fusarium acuminatum, F. avenaceum, F. concolor, F. crookwellense (F. cerealis), F. equiseti, F. semitectum, F. solani, F. sporotrichioides and F. venenatum, were all present at frequencies < 8%. Our results indicate that economically important Fusarium spp. may be isolated from numerous alternative hosts during the off season and that weeds and plant debris can serve as a reservoir of genetically diverse inoculum.     

Functional characterization of the recombinant antimicrobial peptide Trx-<Emphasis Type="Italic">Ace</Emphasis>-AMP1 and its application on the control of tomato early blight disease

Ace-AMP1 is a potent antifungal peptide found in onion (Allium cepa) seeds with sequence similarity to plant lipid transfer proteins. Transgenic plants over-expressing Ace-AMP1 gene have enhanced disease resistance to some fungal pathogens. However, mass production in heterologous systems and in vitro application of this peptide have not been reported. In this study, Ace-AMP1 was highly expressed in a prokaryotic Escherichia coli system as a fusion protein. The purified protein inhibited the growth of many plant fungal pathogens, especially Alternaria solani, Fusarium oxysporum f. sp. vasinfectum, and Verticillium dahliae. The inhibitory effect was accompanied by hyphal hyperbranching for V. dahliae but not for F. oxysporum f. sp. vasinfectum and A. solani, suggesting that the mode of action of Ace-AMP1 on different fungi might be different. Application of Ace-AMP1 on tomato leaves showed that the recombinant protein conferred strong resistance to the tomato pathogen A. solani and could be used as an effective fungicide.     

Association of Criconemella xenoplax and Fusarium spp. with Root Necrosis and Growth of Peach

Criconemella xenoplax, Fusarium solani, and F. oxysporum caused necrosis of Nemaguard peach feeder roots in greenhouse tests. Root necrosis was more extensive in the presence of either fungus than wtih C. xenoplax alone. Shoot growth and plant height were less for plants inoculated with F. oxysporum or F. solani than for plants inoculated with the fungi plus C. xenoplax. Neither synergistic nor additive effects on root necrosis or plant growth occurred between C. xenoplax and the fungal pathogens.     

The synthetic strigolactone GR24 influences the growth pattern of phytopathogenic fungi

Strigolactones that are released by plant roots to the rhizosphere are involved in both plant symbiosis with arbuscular mycorrhizal fungi and in plant infection by root parasitic plants. In this paper, we describe the response of various phytopathogenic fungi to the synthetic strigolactone GR24. When GR24 was embedded in the growth medium, it inhibited the growth of the root pathogens Fusarium oxysporum f. sp. melonis, Fusarium solani f. sp. mango, Sclerotinia sclerotiorum and Macrophomina phaseolina, and of the foliar pathogens Alternaria alternata, Colletotrichum acutatum and Botrytis cinerea. In the presence of this synthetic strigolactone, intense branching activity was exhibited by S. sclerotiorum, C. acutatum and F. oxysporum f. sp. melonis. Slightly increased hyphal branching was observed for A. alternata, F. solani f. sp. mango and B. cinerea, whereas suppression of hyphal branching by GR24 was observed in M. phaseolina. These results suggest that strigolactones not only affect mycorrhizal fungi and parasitic plants, but they also have a more general effect on phytopathogenic fungi.     

Dryopteris crassirhizoma Dryocrassin ABBA for Postharvest Control of the Potato Dry Rot Pathogen Fusarium solani var. coeruleum

Dryopteris crassirhizoma dryocrassin ABBA treatment was tested for its effectiveness in controlling Fusarium solani var. coeruleum growth in vitro and for prevention of postharvest dry rot of potato tubers and slices. Dryocrassin ABBA strongly inhibited mycelial growth, resulting in reductions in both mycelium dry weight and per cent spore germination of F. solani var. coeruleum at concentrations of 2.0, 0.5 and 0.1 mg/ml. Scanning electron microscopy (SEM) observations showed that treatment induced abnormal, tightly twisted morphological changes in hyphae. Moreover, in vivo experiments demonstrated that dryocrassin ABBA treatment at 2 mg/ml effectively controlled dry rot of potato tubers inoculated with mycelial discs of F. solani var. coeruleum. After dryocrassin ABBA treatment, the content of soluble proteins, peroxidase (POD) and superoxide dismutase (SOD) activity increased, and malondialdehyde (MDA) content remained the stable situation. In addition, the expression level of plant lipid‐transfer proteins (LTPs) genes – StLTPa1, StLTPa7, StLTPb1 and StLTPb3 – was upregulated. These results collectively demonstrate that dryocrassin ABBA can inhibit growth of Fusarium pathogens to induce disease resistance. On the other side, dryocrassin ABBA maybe induce potato defence responses.     

Antifungal activity of aluminium‐containing salts against the development of carrot cavity spot and potato dry rot

As an alternative to the use of synthetic chemical fungicides to control plant disease, aluminium‐containing salts were evaluated for their effects on the mycelial growth of various fungal or fungus‐like pathogens and their ability to control carrot cavity spot (Pythium sulcatum) and potato dry rot (Fusarium sambucinum). Results showed that various aluminium‐containing salts provided strong inhibition of all the tested pathogens (Alternaria solani, Botrytis cinerea, F. sambucinum, P. sulcatum and Rhizopus stolonifer) with minimal inhibitory concentration of 1–10 mM. Aluminium chloride and aluminium sulphate were generally the most effective, inhibiting mycelial growth of pathogens by as much as 47% and 100%, respectively, at a salt concentration of 1 mM. Applied at 5 mM, aluminium sulphate also provided 28% and 100% inhibition of dry rot and cavity spot, respectively. Aluminium chloride (5 mM) reduced dry rot by 25% whereas aluminium lactate (5 mM) decreased cavity spot lesions by 86%. These results indicate that various aluminium‐containing salts may provide an alternative to the use of synthetic fungicides to control these pathogens.     

Fungi associated with black pepper plants in Quang Tri province (Vietnam), and interaction between Meloidogyne incognita and Fusarium solani

During a survey of nurseries and plantations of black pepper plants in Quang Tri province in Vietnam during the rainy season of 2007, nine fungal taxa were isolated from the roots of the black pepper plants. Fusarium solani was found in about one out of four black pepper root samples examined but not in the nurseries and also not from black pepper plants younger than five years growing in plantations. Since in these nurseries about one out of two black pepper plants examined had yellow leaves, this observation suggests that another pathogen must be the initial cause of the yellowing of the leaves. A likely pathogenic candidate is M. incognita which was extracted from every single black pepper plant examined in the nurseries. During the same survey, we also observed that F. solani was not isolated from the roots of black pepper plants that did not had yellow leaves and that the percentage of black pepper plants with yellow leaves increased with increased frequency of occurrence of F. solani. This observation indicates that F. solani plays a role in the yellowing of the leaves of black pepper plants in a later stage of the development of the plants. The results of a greenhouse experiment showed the negative effects inoculation with M. incognita alone or in combination with F. solani may have on the percentage of black pepper plants with yellow leaves and on plant growth. No effect of inoculation with F. solani before, at the same time, or two weeks after inoculation with M. incognita on root galling and nematode reproduction was observed.     

Combination of Pseudomonas aeruginosa and Pochonia chlamydosporia for Control of Root-Infecting Fungi in Tomato

A plant growth‐promoting rhizobacterium, Pseudomonas aeruginosa strain IE‐6, and a fungal antagonist, Pochonia chlamydosporia, were tested for their ability to inhibit mycelial growth of root‐infecting fungi under laboratory conditions including Macrophomina phaseolina, Fusarium oxysporum, F. solani and Rhizoctonia solani. Biocontrol effectiveness of the bacterium and the fungus alone or in combination was also determined for the control of root‐infecting fungi under field conditions. In a dual‐culture plate assay, the colonies of P. chlamydosporia and P. aeruginosa met each other and no further growth of either organism occurred. Against M. phaseolina, F. solani and R. solani, an ethyl acetate extract of the culture filtrates of P. aeruginosa inhibited fungal growth greater than the hexane extract, but against F. oxysporum the hexane extract caused greater inhibition of fungal growth. By contrast, against M. phaseolina, F. oxysporum and F. solani, the hexane extract of P. chlamydosporia was more effective in the inhibition of fungal growth than the ethyl acetate fraction. Ethyl acetate extracts of P. aeruginosa at 1.0 mg/ml not only inhibited the radial colony growth of R. solani but also lysed the fungal mycelium. P. aeruginosa produced siderophores and hydrogen cyanide under laboratory conditions. Field experiments conducted in 1997 and repeated in 1998 revealed that Pochonia chlamydosporia and P. aeruginosa significantly suppressed the root‐infecting fungi M. phaseolina, F. oxysporum, F. solani and R. solani and that the combination of the two caused greater inhibition of the fungal pathogens than either alone. Application of P. chlamydosporia and P. aeruginosa as a soil drench also resulted in enhanced growth of tomato plants.     

Phytopathogenic Fusarium oxysporum Schlecht, as a Necrotrophic Mycoparasite

Fusarium oxysporum f. sp. dianthi, f. sp. lycopersici, f. sp. cepae, f. sp. niveum and one unidentified F. oxysporum isolate proved to be active necrotrophic mycoparasites. In dual cultures hyphae of Trichoderma hamatum, T. longibrachiatum, T. pseudokoningii, T. harzianum, Botrytis cinerea and Rhizoctonia solani were parasitized and destroyed by F. oxysporum. One isolate of Phytophthora sp. was not affected. Mutual parasitism between F. oxysporum and T. pseudokoningii and T. longibrachiatum has been observed, too. Details of parasitic hyphal interactions: hyphal coiling, penetration sites, resistance sheat formation, hyphal invasion and internal growing are described. The mycoparasitic feature as well as antimicrobial metabolic production of F. oxysporum is probably a common phenomenon to ensure this important plant pathogenic species to compete successfully against other soil-borne fungal pathogens and saprophytes.     

Somatic Hybrids Between Potato and S. berthaultii Show Partial Resistance to Soil‐Borne Fungi and Potato Virus Y

Three tetraploid somatic hybrid lines produced by protoplast fusion between a dihaploid potato, Solanum tuberosum, cultivar BF15 and the wild potato species Solanum berthaultii were evaluated here for their response to different soil‐borne pathogens, that is Fusarium solani, Pythium aphanidermatum and Rhizoctonia solani as well as to infection by potato virus Y (PVY). Both hybrid and BF15 plants grown in vitro were inoculated with the tested pathogen strains, that is R. solani, P. aphanidermatum, or F. solani. The growth level and disease severity index of these plants were compared to the susceptible commercial cultivar Spunta. A better growth of inoculated hybrid plants and restricted disease symptoms were observed in comparison with the commercial plants. Under glasshouse conditions and after inoculation with R. solani and P. aphanidermatum, improved resistance of the hybrid plants to these pathogens was confirmed. Indeed, these plants showed no significant damage following inoculation and a better development in R. solani‐infected plants. The susceptibility of the hybrid tubers to R. solani, P. aphanidermatum, and to F. solani infection was also determined. A significant reduction of tissue colonisation was observed in all the hybrid lines compared to the cultivated cultivars. The STBc and STBd hybrids also showed improved resistance to the PVY ordinary strain (PVY^o) under glasshouse conditions.     

Seasonal accumulation and partitioning of nitrogen by lentil

Although wheat (Triticum aestivum L.) is the dominant crop of the semi-arid plains of Canada and the western United States, lentil (Lens culinaris Medik.) has become an important alternative crop. Sources and seasonal accumulation of N must be understood in order to identify parameters that can lead to increased N₂-fixing activity and yield. Inoculated lentil was grown in a sandy-loam soil at an irrigated site in Saskatchewan, Canada. Wheat was used as the reference crop to estimate N₂ fixation by the A-value approach. Lentil and wheat received 10 and 100 kg N ha⁻¹ of ammonium nitrate, respectively. Crops were harvested six times during the growing season and plant components analyzed. During the first 71 days after planting the wheat had a higher daily dry matter and N accumulation compared to lentil. However, during the latter part of the growing season, daily dry matter and N accumulation were greater for lentil. The maximum total N accumulation for lentil at maturity was 149 kg ha⁻¹. In contrast, wheat had a maximum N accumulation of 98 kg ha⁻¹ in the Feekes 11.1 stage, or 86 days after planting. The maximum daily rates of N accumulation were 3.82 kg N ha⁻¹ day⁻¹ for lentil and 2.21 kg N ha⁻¹ day⁻¹ for wheat. The percentage of N derived from N₂ fixation (% Ndfa) ranged from 0 at the first harvest to 92 % at final harvest. Generative plant components had higher values for % Ndfa than the vegetative components which indicates that N in the reproductive plant parts was derived largely from current N₂ fixation and lentil continued to fix N until the end of the pod fill stage. At final harvest, lentil had derived 129 kg N ha⁻¹ from N₂ fixation with maximum N₂-fixing activity (4.4 kg N ha⁻¹ day⁻¹) occurring during the early stages of pod fill. Higher maximum rates of N₂-fixing activity than net N accumulation (3.82 kg N ha⁻¹ day⁻¹) may have been caused by N losses like volatilization. In addition, lentil provided a net N contribution to the soil of 59 kg ha⁻¹ following the removal of the grain.     

Sugar Beet-Associated Bacterial and Fungal Communities Show a High Indigenous Antagonistic Potential Against Plant Pathogens

The aim of this study was to analyze microbial communities in/on sugar beet with special focus on antagonists toward plant pathogens. For this purpose, the composition of microorganisms isolated from the rhizosphere, phyllosphere, endorhiza, and endosphere of field-grown sugar beet plants was analyzed by a multiphasic approach at three different plant development stages at six locations in Europe. The analysis of microbial communities by Single Strand Conformation Polymorphism (SSCP) of 16S/18S rRNA clearly revealed the existence of discrete microenvironment- and site-specific patterns. A total of 1952 bacterial and 1344 fungal isolates screened by dual testing for antagonism toward the pathogens Aphanomyces cochlioides, Phoma betae, Pythium ultimum, and Rhizoctonia solani resulted in 885 bacterial (=45%) and 437 fungal (=33%) antagonists. In general, the indigenous antagonistic potential was very high and influenced by (a) the location, (b) the plant developmental stage, and (3) the microenvironment. Furthermore, we showed for the first time that the antagonistic potential was highly specific for each target pathogen. The majority of antagonistic microorganisms suppressed only one pathogen (bacteria: 664 = 75%; fungi: 256 = 59%), whereas the minority showed a broad host range (bacteria: 4 = 0.5%; fungi: 7 = 1.6%). The bacterial communities harbored the highest antagonistic potential against P. ultimum, whereas the fungal communities contained more antagonists against A. cochlioides and R. solani. In contrast to their high proportion, only a low diversity of antagonists at genotypic and species level was found. Novel antagonistic species, e.g., Subtercola pratensis or Microbacterium testaceum were found in the internal part of the sugar beet body.     

Identity and Pathogenicity of Fungi Associated with Root and Crown Rot of Soft Red Winter Wheat Grown on the Upper Coastal Plain Land Resource Area of Mississippi

Seedling stand, disease severity and fungal incidence were determined from untreated ‘Wakefield’ soft red winter wheat planted on a Leeper silty clay loam in field tests conducted at the Mississippi Agricultural and Forestry Experiment Station, Plant Science Research Center, Mississippi State University, Starkville, Mississippi during the 1996–97 and 1997–98 growing seasons. Seedling stand was reduced by 40% each year in plots established with untreated seed. Cochliobolus sativus was the most frequently isolated fungus. Fusarium acuminatum, Fusarium equiseti and Fusarium solani were the most prevalent Fusarium spp. Seven other Fusarium spp. and 23 species of other fungal genera were isolated. Pathogenicity tests with three isolates each of C. sativus, Cochliobolus spicifer, F. acuminatum, F. solani, F. equiseti, Fusarium compactum, Embellisia chlamydospora and Microdochium bolleyi were performed in test tube culture and two isolates each of C. sativus, C. spicifer, F. acuminatum, E. chlamydospora and M. bolleyi under greenhouse conditions. In test tubes and in the greenhouse, seedlings infected with isolates of C. sativus developed seedling blight, discoloration and necrosis, primarily in seminal roots and crowns. In the greenhouse, C. sativus induced lesions on the lower leaf sheath and reduced seedling height, seedling emergence, dry and fresh weight of roots and shoots. Isolates of F. acuminatum, F. solani, F. equiseti, F. compactum, E. chlamydospora and M. bolleyi induced slight to moderate orange to light‐brown discoloration of crown and seminal roots in test tubes. Cochliobolus spicifer isolates had the most pre‐emergence activity, inducing black root discoloration and root pruning of wheat seedlings and reducing seedling emergence, root fresh weight and shoot dry weight. In the greenhouse, F. acuminatum reduced seedling height, seedling emergence and root and shoot dry weights. Microdochium bolleyi and E. chlamydospora reduced fresh and dry weight of roots, plant emergence and shoot dry weight. Fusarium acuminatum and C. spicifer reduced the growth rate of wheat seedlings. All fungi evaluated showed increased disease severity compared to the untreated control. The high frequency of isolation of C. sativus from crown and root tissues can be partially explained by the dry, warm conditions during the early stages of wheat seedling development in the Upper Coastal Plain Land Resource Area of Mississippi.     

Evaluation of antifungal activity of food additives against soilborne phytopathogenic fungi

The efficacy of eight food additives as possible alternatives to synthetic fungicides for the control of soilborne pathogens, Fusarium oxysporum f. sp. melonis, Macrophomina phaseolina, Rhizoctonia solani, and Sclerotinia sclerotiorum was evaluated in this study. A preliminary selection of food additives was performed through in vitro tests. The ED₅₀, minimum inhibition concentration (MIC), and minimum fungicidal concentration (MFC) values showed that ammonium bicarbonate and potassium sorbate were more toxic to soilborne pathogens compared to other food additives with few exceptions and, therefore selected for further testing in soil. The inhibitory and fungistatic efficacy potassium sorbate were higher than that of ammonium bicarbonate in in vitro tests. Potassium sorbate completely inhibited F. oxysporum f. sp. melonis, M. phaseolina, and R. solani at 0.6% in soil tests. In contrast ammonium bicarbonate at 0.6% was inferior compared to potassium sorbate. Ammonium bicarbonate achieved to control all fungi at 2% that is the highest concentration used in this study. Potassium sorbate showed higher toxicity to all fungi compared to ammonium bicarbonate in soil tests. Both ammonium bicarbonate and potassium sorbate increased the pH of soil. The rate of pH increase was higher in ammonium bicarbonate.