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Phytopathogens and food-borne pathogens are a major threat to human health, so there is an urgent need to find some alternatives to overcome these issues. Nanomaterials have shown great potential as antimicrobials therefore, in this study, ZnO nanoparticles were synthesized using Azadirachta indica leaf extract and studied for their antimicrobial activity. Their antimicrobial efficacy was studied against phyto and food borne pathogens and compared with the commercially available chemically synthesized ZnO nanoparticles (Chem-ZnO-NPs). The Azadirachta indica synthesized ZnO-NPs were characterized using UV–VIS spectroscopy, DLS, and FTIR. DLS data depicts that the size of nanoparticles in colloidal solution is approximately 96 nm, with polydispersity index (PDI) of 0.37. The antimicrobial activity was studied using pour plate method. The MIC data for food borne pathogens (E. coli and S. aureus) shows that Azadirachta indica mediated ZnO-NP are more efficient as compared to Chem-ZnO-NPs. For phytopathogens (Alternaria alternata, Sclerotium rolfsii and Stemphylium solani) also the result shows that Azadirachta indica mediated ZnO-NP exhibit more efficient antifungal properties. Therefore, the synthesized ZnO-NP can be efficiently used in place of commercially available fungal pesticides.

Seed borne diseases can easily spread from one place to another and serve as an initial source of inoculum. Mycoflora are causative agents of devastating tomato diseases like early blight, fusarium wilt, root and fruit rots. A total of 100 tomato seed samples of cultivar PKM 1 were collected from seed producers and farmers across different agro climatic regions of Tamilnadu and screened for their seed borne mycoflora. A total of 14 species of fungi viz., Alternaria solani, Alternaria alternata, Stemphylium solani, Fusarium moniliforme, Fusarium oxysporum, Colletotrichum capsici, Curvularia lunata, Aspergillus niger, Aspergillus flavus, Rhizopus nigricans, Helminthosporium solani, Pythium debaryanum, Rhizoctonia solani and Phytophthora infestans were recovered from the collected seed samples using various seed health testing methods. Isolated plant pathogens, were tested for their pathogenicity and transmission on tomato cultivar PKM 1 seedlings.

The aim of this study was to identify a Mexican native basidiomycete strain with antagonistic potential against phytopathogenic fungi. The antifungal activity of fifteen isolates against Fusarium oxysporum, Fusarium solani, Colletotrichum truncatum, Colletotrichum coccodes, Colletotrichum sp., Stemphylium solani, Botrytis cinerea, Epicoccum nigrum, Phomopsis sp. and Alternaria solani was studied in vitro using dual culture assay. An isolate of Macrolepiota sp (CS185) exhibited the strongest ability to compete on potato dextrose agar medium (PDA) causing 22.2 up to 46.6% inhibition in seven out of ten pathogens evaluated. The addition of 30% Macrolepiota sp. liquid filtrates (from 7 day-cultures in potato dextrose broth) to PDA plates inhibited 66% of A. solani growth. Application of Macrolepiota sp. CS185 culture fluids to control early blight disease caused in tomato plants by A. solani under greenhouse conditions diminished disease incidence and percent of damage. The length of the stems, the roots and the foliar area increased in the treated plants and, above all, the foliar symptoms decreased by 73%. Sesquiterpene lactones and quinones identified in culture fluids might be responsible for Macrolepiota antifungal activity. This study proves that Macrolepiota sp. CS185 culture filtrates have potential in biocontrol of early blight disease.

In the present study, novel mixed additives of Chitosan or Paraloid B-72 combined with nanoparticles (NPs) of Ag, ZnO, or cellulose (NCL) were examined for their effects on the mechanical, optical, and fungal inhibition properties of the papersheets produced. The highest tensile, tear, and burst indices of the papersheets were observed for flax pulp treated with additives of Paraloid B-72 + ZnO NP (1%), Chitosan + ZnO NP (3%), and Chitosan + NCL (3%) at levels of 59.93 N&middot, m/g, 18.45 mN&middot, m2/g, and 6.47 kPa&middot, m2/g, respectively. Chitosan + ZnO NP (1%) added to flax pulp showed the highest fungal mycelial inhibition (FMI) (1.85%) against Aspergillus flavus. Chitosan + Ag NP (1%) exhibited the highest FMI percentage (11.48%) when added to pulp against A. terreus. Pulp treated with Paraloid B-72 + Ag NP (1%) exhibited the highest activity against Stemphylium solani with an FMI value of 3.7%. The results indicate that the technological properties of the papersheets were enhanced with the addition of novel mixtures to the pulp.

Development of crop protective products with natural origin as alternative to synthetic fungicides have been in focus, because they present low environmental impact when compared to conventional pesticides. A total of ten essential oils were chemically characterized and tested for antifungal activity against Stemphylium solani, which causes gray leaf spot on tomato. All essential oils showed antifungal activity against the fungus tested. Essential oils of Aloysia citrodora (citral) and Eucalyptus staigeriana (citral), Cinnamomum camphora (linalool) and Foeniculum vulgare (anethole), proved to be the most effectives, showing 100% inhibition of mycelial growth at maximum concentration of 2.5 µL mL-1. Essential oils were also evaluated for their phytotoxicity on tomato. Volatile effect of E. staigeriana, Eucalyptus globulus and Baccharis trimera oils reduced seedling growth, however the other tested oils had no volatile effect on tomato seeds and seedlings. Contact effect of all essential oils presented negative response on germination of seeds and development of seedlings. Thus, the essential oils used in this study presented fungicidal action and could be used for the development of new environmental friendly products for controlling phytopathogen on tomato, however further formulation and field application form are necessary to achieve this target.

Some Stemphylium isolates reported from Malaysia as well as other regions of the world have been identified by morphology and blast analysis of the ITS region only, and eventually deposited in NCBI GenBank. To our knowledge, some of these isolates have been misidentified. The re-examination of identity of all Stemphylium isolates reported from Malaysia using morphological and phylogenetic analyses of the ITS and gpd, as well as phylogenetic analyses of all isolates of S. lycopersici and S. solani available in NCBI GenBank from other regions of the world indicated that a remarkable number of isolates deposited in NCBI GenBank under S. lycopersici and S. solani species were misidentified.

Stemphylium solani is an important foliar pathogen that infects many agricultural plants, especially solanaceous plants. The difficulty inducing sporulation in pure culture is a limiting factor for research on the different pathosystems involving S. solani. In this study, the influence of the culture medium, photoperiod with alternating temperatures, Petri dish cover materials (glass, polystyrene and PVC film) and stress factors of the colonies were investigated in the conidia production. Six sequential assays were performed with four isolates of S. solani, obtained from tomato plants. The inoculum produced was evaluated for infectivity on tomato plants under greenhouse conditions. The addition of fresh tomato juice to the agar medium and incubation temperatures of approximately 25 °C favoured mycelial growth. The ability to sporulate in vitro varied with the isolate, but in general the conidia production was significantly higher in V8 medium at 25 °C 6 h−1 light and 10 °C 18 h−1 of darkness. Sporulation was lower in glass Petri dishes but higher in transparent polystyrene dishes. The methodology allowed the production of viable and infective inoculum in sufficient quantity to inoculate plants under experimental conditions.

Alternative methods of fungal biocontrol are required, and this paper looks at natural sources of products which can be produced and used without significant risk to human health and the environment, thereby reducing the need for toxic pesticides. Even after the significant expenditures on agrochemical control agents, a significant fraction of agriculture production is regularly lost due to fungal diseases. Species of Ulva are known to produce bioactive substances that can induce plant resistance to diseases. Before committing to the extensive use of extracts from such algal sources as elicitors in agriculture, it is essential to confirm the specificity of their antifungal activities. This study, examined whether extracts and dried, milled flour of Ulva fasciata demonstrated antifungal activity against the commercially important pathogen, Stemphylium solani. Samples of S. solani were obtained from infected leaves of the tomato Solanum lycopersicum and were cultured on Potato-Dextrose-Agar medium, with three added concentrations of ulvan and flour obtained from U. fasciata (0.1; 0.5 and 1.0 g·L− 1), in a BDO chamber, at 25 °C, for 10 days in the dark. The diameter of the mycelia was used as the parameter for fungal growth. Neither the flour nor ulvan from U. fasciata showed any direct anti-fungal activity, but the presence of compounds produced by U. fasciata showing antagonist physiological effects against S. solani should be investigated.

Since 1994, tomato (Lycopersicon esculentum Mill.) grown in Mérida State, located in the Venezuelan Andes, have been consistently affected by a gray leaf spot disease with symptoms on leaves, petioles, and stems. Yield is reduced, and in some cases entire crops have been destroyed over short time. Because of its prevalence, distribution, and severity, the disease has become the major factor limiting tomato production in this region. Disease symptoms were commonly observed on seedlings and plants. On leaves the disease first appeared as circular to elongated dark specks. As the spots enlarged, they became gray and bright. Old lesions dried and usually cracked. Severely infected leaves turned yellow and then died and dropped. Lesions on petioles and stems were elongate. Disease severity was generally higher following the beginning of fruiting. The fungus was isolated from leaves, petioles, and stems of tomato cv. Rio Grande on 2% water agar acidified with lactic acid. On potato-carrot agar, conidiophores and conidia were produced with the characteristics of Stemphylium. Two species of Stemphylium, S. solani G. F. Weber and S. lycopersici (Enjoji) W. Yamamoto, cause gray leaf spot symptoms on tomato. Based on morphology, size, and the length/width ratio of the conidia, the fungus was identified as S. solani (1). Inoculations done by spraying a conidial suspension on plants of tomato cv. Rio Grande produced symptoms similar to those observed in the field. S. solani was consistently isolated from experimentally infected tissues, thus confirming Koch's postulates. This is the first report of S. solani causing gray leaf spot on tomato grown in the Andes of Venezuela. Reference: (1) G. F. Weber. Phytopathology 20:513, 1930.

A severe epidemic of a leaf blight of cotton occurred in the state of Paraná, Brazil, during 1994 and 1995, causing up to 100% yield losses in some commercial fields of cultivar Paraná 3. The severity of the disease among fields was variable and cultivar-dependent. Attempts were made to identify the organism causing the leaf blight symptoms, which were characterized as circular to irregular dark brown to black spots turning reddish brown with age and varying between 2 and 10 mm in diameter. The older lesions showed cracks and/or holes in the center. Severely diseased leaves dried rapidly and abscised. Fructifications of a fungus in the genus Stemphylium were observed on young, as well as on old, lesions. The Stemphylium sp. was consistently isolated on potato dextrose agar from disease samples collected from five cultivars in 14 locations. In inoculation tests, the Stemphylium isolates from cotton were highly aggressive to cotton, tomato, potato, and blue lupines; whereas an isolate of S. solani from tomato was highly aggressive on tomato and potato but less aggressive on cotton. On the basis of its morphological, cultural, and pathogenic characteristics, the principal pathogen causing leaf blight symptoms was identified as Stemphylium solani. Epidemics caused by S. solani on cotton have not been reported previously in commercial cotton cultivation.

In June 2011, tomatoes (Solanum lycopersicum) in major growing areas of the Cameron Highlands and the Johor state in Malaysia were affected by a leaf spot disease. Disease incidence exceeded 80% in some severely infected regions. Symptoms on 50 observed plants initially appeared on leaves as small, brownish black specks, which later became grayish brown, angular lesions surrounded by a yellow border. As the lesions matured, the affected leaves dried up and became brittle and later developed cracks in the center of the lesions. A survey was performed in these growing areas and 27 isolates of the pathogen were isolated from the tomato leaves on potato carrot agar (PCA). The isolates were purified by the single spore technique and were transferred onto PCA and V8 agar media for conidiophore and conidia production under alternating light (8 hours per day) and darkness (16 hours per day) (4). Colonies on PCA and V8 agar exhibited grey mycelium and numerous conidia were formed at the terminal end of conidiophores. The conidiophores were up to 240 μm long. Conidia were oblong with 2 to 11 transverse and 1 to 6 longitudinal septa and were 24 to 69.6 μm long × 9.6 to 14.4 μm wide. The pathogen was identified as Stemphylium solani on the basis of morphological criteria (2). In addition, DNA was extracted and the internal transcribed spacer region (ITS) was amplified by universal primers ITS5 and ITS4 (1). The PCR product was purified by the commercial PCR purification kit and the purified PCR product sequenced. The resulting sequences were 100% identical to published S. solani sequences (GenBank Accestion Nos. AF203451 and HQ840713). The amplified ITS region was deposited with NCBI GenBank under Accession No. JQ657726. A representative isolate of the pathogen was inoculated on detached 45-day-old tomato leaves of Malaysian cultivar 152177-A for pathogenicity testing. One wounded and two nonwounded leaflets per leaf were used in this experiment. The leaves were wounded by applying pressure to leaf blades with the serrated edge of a forceps. A 20-μl drop of conidial suspension containing 105 conidia/ml was used to inoculate these leaves (3). The inoculated leaves were placed on moist filter paper in petri dishes and incubated for 48 h at 25°C. Control leaves were inoculated with sterilized distilled water. After 7 days, typical symptoms for S. solani similar to those observed in the farmers' fields developed on both wounded and nonwounded inoculated leaves, but not on noninoculated controls, and S. solani was consistently reisolated. To our knowledge, this is the first report of S. solani causing gray leaf spot of tomato in Malaysia. References: (1) M. P. S. Camara et al. Mycologia 94:660, 2002. (2) B. S. Kim et al. Plant Pathol. J. 15:348, 1999. (3) B. M. Pryor and T. J. Michailides. Phytopathology 92:406, 2002. (4) E. G. Simmons. CBS Biodiversity Series 6:775, 2007.

Wild eggplant (Solanum torvum) has been used as a rootstock for eggplant propagation in China for decades. In the winter of 2011–2012, a severe disease with typical symptoms of small brown spots was observed on the leaves of wild eggplant in Chengmai County, Hainan Province, China. This disease had an incidence of about 30–65% among all the plants in the region (about 2 hectares in total). The causal pathogen was identified as Stemphylium solani based on morphological features, cultural characteristics and molecular identification. The pathogenicity was confirmed by Koch’s postulates. This is the first report of natural infection by S. solani causing leaf spot on wild eggplant in China.

International audience; Qualitative plant resistance mechanisms and pathogen virulence have been extensively studied since the formulation of the gene-for-gene hypothesis. The mechanisms involved in the quantitative traits of aggressiveness and plant partial resistance are less well-known. Nevertheless, they are prevalent in most plant-necrotrophic pathogen interactions, including the Daucus carota–Alternaria dauci interaction. Phytotoxic metabolite production by the pathogen plays a key role in aggressiveness in these interactions. The aim of the present study was to explore the link between A. dauci aggressiveness and toxin production. We challenged carrot embryogenic cell cultures from a susceptible genotype (H1) and two partially resistant genotypes (I2 and K3) with exudates from A. dauci strains with various aggressiveness levels. Interestingly, A. dauci-resistant carrot genotypes were only affected by exudates from the most aggressive strain in our study (ITA002). Our results highlight a positive link between A. dauci aggressiveness and the fungal exudate cell toxicity. We hypothesize that the fungal exudate toxicity was linked with the amount of toxic compounds produced by the fungus. Interestingly, organic exudate production by the fungus was correlated with aggressiveness. Hence, we further analyzed the fungal organic extract using HPLC, and correlations between the observed peak intensities and fungal aggressiveness were measured. One observed peak was closely correlated with fungal aggressiveness. We succeeded in purifying this peak and NMR analysis revealed that the purified compound was a novel 10-membered benzenediol lactone, a polyketid that we named ‘aldaulactone’. We used a new automated image analysis method and found that aldaulactone was toxic to in vitro cultured plant cells at those concentrations. The effects of both aldaulactone and fungal organic extracts were weaker on I2-resistant carrot cells compared to H1 carrot cells. Taken together, our results suggest that: (i) aldaulactone is a new phytotoxin, (ii) there is a relationship between the amount of aldaulactone produced and fungal aggressiveness, and (iii) carrot resistance to A. dauci involves mechanisms of resistance to aldaulactone.

In this study, 3-methyl-1,2,4-triazolyl chitosan (MTACS) and 3-chloromethyl-1,2,4-triazolyl chitosan (CMTACS) were prepared via cyclization of acyl thiourea chitosan (TUCS). Their structures were confirmed by FT-IR, 1H-NMR, elemental analysis, DSC, XRD, and SEM. The conformations were predicted using the Gaussian 09 program. Additionally, the antifungal properties of MTACS and CMTACS against Stemphylium solani weber (S. solani), Alternaria porri (A. porri), and Gloeosporium theae-sinensis (G. theae-sinensis) were assayed in vitro and ranged from 250 μg/mL to 1000 μg/mL. The results showed that MTACS and CMTACS exhibited enhanced inhibitory effect on the selected fungi compared to the original chitosan and TUCS. In particular, they displayed better antifungal activities against A. porri and G. theae-sinensis than that of the positive control, Triadimefon. The findings described here may lead to them being used as antifungal agents for crop protection.

An outbreak of grey leaf spot caused by Stemphylium solani was observed on tomato in Shandong Province of China in recent years and brought huge economical losses. Fludioxonil is a phenylpyrrole fungicide with strong antifungal activity against S. solani. To evaluate the risk of S. solani developing fludioxonil resistance, a total of 145 field isolates were examined for sensitivity to fludioxonil by measuring mycelial growth. The baseline sensitivity was distributed as a unimodal curve with a mean EC50 value of 0.0659 (±0.0170) µg mL−1. Five mutants with high resistance to fludioxonil (RF > 1000) were obtained by successively selecting on fludioxonil-amended plates in the laboratory. All the resistant mutants associated with strongly reduced fitness in mycelial growth, sporulation and pathogenicity. Fludioxonil had positive cross-resistance with procymidone and iprodione, but there was no cross-resistance with other fungicides including boscalid, fluazinam, azoxystrobin and flusilazole. Based on the current results, resistance risk of S. solani to fludioxonil could be moderate. This is the first report of baseline sensitivity of S. solani to fludioxonil and its risk assessment. In order to delay the resistance development, it is recommended that fludioxonil can be used as one component of the mixture or fungicides with different modes of action should be alternatively used for this disease management.

Stemphylium solani isolates infect two varieties of eggplant, Solanum aethiopicum and Solanum melongena grown in Senegal (West Africa) and are morphologically quite similar. Using the random amplified polymorphic DNA (RAPD) procedure with arbitrary 10-mer primers, we were able to differentiate these S. solani isolates into two groups directly related to their plant host origin. A RAPD product of approximately 480 bases pairs obtained with OPF-20 primer were polymorphic between the two groups. Four new primers (F20F1, F20F2, F20R1 and F20R2) based on nucleotide sequence analysis of this 480 bases pairs RAPD fragment were developed. Such primers used pairwise amplified a single fragment from the DNA of S. solani isolates whatever their host origin. However, DNA extracted from Fusarium oxysporum (f. sp. vasinfectum, f. sp. elaeidis), Verticillium dahliae and Phyllosticta sp. isolates did not amplify using these primers. Our results indicate that these primers sets were good tools for specific identification of these two eggplants S. solani isolates by polymerase chain reaction (PCR). Key words: Stemphylium solani isolates, Solanum aethiopicum, Solanum melongena, random amplified polymorphic DNA (RAPD) markers, identification.

During 2010–2011, a severe leaf spot disease of sweet potato (Ipomoea batatas) was found in Haikou City, Hainan province of China. The disease is characterized with large, irregular, brown, necrotic lesions on the margin or in the centre of leaves. A species of Stemphylium was consistently recovered from pieces of symptomatic tissues on PDA. Based on morphological characteristics and molecular identification by rDNA-ITS gene analysis, the fungal species was identified as Stemphylium solani Weber, and its pathogenicity was confirmed by Koch's postulates. This is the first report of leaf spot on sweet potato caused by S. solani in China.

With an aim to discover novel chitosan derivatives with enhanced antifungal properties compared with chitosan. Diethyl dithiocarbamate chitosan (EtDTCCS) was investigated and its structure was well identified. The antifungal activity of EtDTCCS against Alternaria porri (A. porri), Gloeosporium theae sinensis Miyake (G. theae sinensis), and Stemphylium solani Weber (S. solani) was tested at 0.25,0.5, and 1.0 mg/mL, respectively. Compared with plain chitosan, EtDTCCS shows better inhibitory effect with 93.2% inhibitory index on G. theae sinensis at 1.0 mg/mL, even stronger than for polyoxin (82.5%). It was inferred derivatives of this kind may find potential applications for the treatment of various crop-threatening diseases. (c) 2014 Elsevier B.V. All rights reserved.

Degradation of chitosan by H2O2 under microwave irradiation was investigated. The oxidative degradation of chitosan was highly accelerated by microwave irradiation under the condition of low temperature and low concentration of H2O2. The degraded chitosans with low molecular weight (M-w) were characterized by gel permeation chromatography, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, X-ray diffraction and elemental analysis. The decrease of M-w led to transformation of crystal structure and increase of water solubility, whereas no significant chemical structure change in the backbone of chitosan was observed. Antifungal activities of chitosans with different M against crop pathogenic fungi Phomopsis asparagi, Fusarium oxysoporum f. sp. Vasinfectum and Stemphylium solani were investigated at the concentrations of 100, 200 and 400 mg/L. All degraded chitosans with low M-w exhibited enhanced antifungal activity compared with original chitosan and the chitosan of 41.2 kDa showed the highest activity. At 400 mg/L, the chitosan of 41.2 kDa inhibited growth of P. asparagi at 89.3%, stronger than polyoxin and triadimefon, the inhibitory effects of which were found to be 55.5% and 68.5%. All the results indicated that oxidative degradation under microwave irradiation was a promising technique for large-scale production of low M-w chitosan for use in crop protection. (C) 2012 Elsevier B.V. All rights reserved.

Guiera senegalensis (Gs) is a well-known traditional medicinal plant in Africa, whose leaves extract and roots powder are used for treatment of diseases and wounds in Western Kordufan, Sudan. The aim of this study was to investigate the phytochemical analysis, toxicity, and the antifungal activity of Gs leaves extract. Extract of the leaves of Gs was tested for its antimicrobial activity against Stemphylium solani, Aspergillus flavus, Trichoderma viride, Penicillium Spp., Fusarium verticillatum, Cladosporium cladosporioides, and Fusarium solani. This present study showed that Gs leaves extract has no inhibition activity against all of the tested fungal strains. On the other hand, the toxicity test, which was conducted by using brine shrimp, suggests that Gs leaves extract is apparently not toxic. The phytochemical screening revealed that Gs leave extract contains alkaloids, flavonoids, terpenoids, tannin, carbohydrates, proteins, steroids, and saponins. The results of this preliminary investigation suggests that the medicinal plant extract may be safe to use as a drink for treatment of various diseases as has been practiced for years in the villages of Western Sudan. More research is needed to investigate if there is any side effect when the extract is taken orally. Further, the medicinal properties of the phytochemical compounds of Gs need to be further investigated.

This study's aim is to isolate and characterize plant growth promoting Enterobacter species for the biological control of gray leaf spot in pepper. Screening was carried out from the rhizosphere of Agropyron tsukushiensi var. transiens (Hack.) Ohwi in Dok-do. Rhizobacterial isolates were partially identified by 16S rDNA sequencing and Enterobacter species were tested for plant growth promoting capabilities and the induction of systemic resistance in pepper against gray leaf spot caused by Stemphylium solani. Isolates were tested for production of indole-acetic acid and siderophore, and for phosphate solubilization. The application of isolates was effective in controlling gray leaf spot in pepper with E. asburiae (KNUC5007) and E. cancerogenes (KNUC5008 and KNUC5010) having the highest efficacy in reducing gray leaf spot severity. This is the first report of the biological control of gray leaf spot in pepper using rhizobacteria and it is hoped that this study will increase the utilization of Enterobacter species as plant growth promoters and biocontrol agents.

Three novel thiosemicarbazone chitosan derivatives were obtained via condensation reaction of thiosemicarbazide chitosan with phenylaldehyde, o-hydroxyphenylaldehyde, and p-methoxyphenylaldehyde, respectively. Antifungal activity against the common crop-threatening pathogenic fungi Stemphylium solani weber (S. solani), Rhizoctonia solani Kahn (R. solani), Alternaria solani (A. solani), and Phomopsis asparagi (Sacc.) (P. asparagi) was tested in vitro at 0.05.0.1. and 0.5 mg/mL. The derivatives had broad-spectrum antifungal activity that was greatly enhanced in comparison with chitosan. In fact, the highest antifungal index reached 100%. At 0.05 mg/mL, the o-hydroxyphenylaldehyde thiosemicarbazone chitosan inhibited growth of R. solani at 52.6%, and was stronger than polyoxin whose antifungal index was found to be 31.5%. The chitosan derivatives described here lend themselves to future applicative studies in agriculture. (C) 2011 Elsevier Ltd. All rights reserved.

Stemphylium solani, the causal agent of leaf blight of garlic (Allium sativum), produced phytotoxic metabolites in culture. A non-host-specific phytotoxin from culture filtrate of S. solani isolate DY-5, named SS-toxin, was extracted by ethyl acetate, isolated by bioassay-guided thin layer chromatography on silica gel, and purified by preparative liquid chromatography. SS-toxin produced necrotic lesions on detached garlic leaves, similar to that caused by S. solani. When wounded leaves were each treated with a 10-μl droplet of toxin, Changbanpo, a garlic cultivar susceptible to leaf blight, showed necrotic lesions at 11 μg/ml toxin, while a resistant cultivar, Qingganruanye, showed symptoms at 44 μg/ml. The effective doses causing 50% inhibition (EC50 values) of root growth and shoot elongation of the susceptible cultivar were 64.9 and 178.5 μg/ml, respectively. The SS-toxin significantly inhibited mitotic activity of root tip cells of the susceptible cultivar from 22 μg/ml and higher causing an abnormally high frequency of cells in interphase. Concentrations over 50 μg/ml of SS-toxin were found to be significantly toxic to total chlorophyll, both chlorophyll a and b, of the susceptible cultivar. The plasma membrane–cell wall interface, nuclear membranes, mitochondria, and chloroplasts were affected by SS-toxin in susceptible leaf cells. This is the first report of the purification and testing of a phytotoxin produced by S. solani.

Leaf blight caused by Stemphylium solani is a major fungal disease of garlic (Allium sativum) in central China where it has caused severe crop losses during the winter growing season from the end of autumn to the middle of spring. Epidemiology, cultivar resistance, and chemical controls were investigated during the 2006 to 2008 growing seasons in Dangyang County to improve disease control methods. Disease severity monitoring revealed that the activity of S. solani was variable between growing seasons, and this may have been due to weather conditions. Disease severity was positively correlated with increasing temperatures, but no consistent relationship was found between total rainfall and disease. Additionally, the study demonstrated that conidia and mycelium of S. solani could survive in garlic debris for long periods and serve as the primary inoculum source for the subsequent season. Relatively few of the commonly grown cultivars had high levels of resistance to leaf blight. Garlic cultivars ‘Qingganrua...

Leaf blight of garlic (Allium sativum) is a severe disease in garlic-growing regions. SS-toxin is a newly described non-proteinaceous toxin produced by the phytopathogenic fungus, Stemphylium solani, the cause of garlic leaf blight. In this study, the effects of SS-toxin on the H+-ATPase activity and standard redox activity in the plasma membranes isolated by aqueous polymer two-phase partitioning from garlic seedling leaves were studied in vitro. The H+-ATPase activity, NADH oxidation rate and Fe(CN) 6 3− reduction rate of the plasma membranes isolated from susceptible and resistant cultivars were all inhibited in a dose-dependent manner. Our results suggest that, under in vitro conditions, the plasma membrane H+-ATPase and standard redox system can be both the cellular targets of SS-toxin.

Plant species introduced into new regions can both leave behind co-evolved pathogens and acquire new ones. Traits important to infection and virulence are subject to rapid evolutionary change in both plant and pathogen. Using Stemphylium solani, a native foliar necrotroph on clovers (Trifolium and Medicago) in California, USA, we explore how plant-fungal interactions may change in an invasion context. After four generations of experimental serial passage through multiple hosts, Stemphylium consistently showed increased infection rates but no consistent change in damage to the host. In a historical opportunity study, we compared infection and virulence across four groups of clover hosts: California natives, European clovers not found in California, and both California and European genotypes of species naturalized in California. There was significant variation among hosts, but no pattern across the four groups. However, in direct comparisons of familiar California genotypes to unfamiliar European genotypes of the same naturalized species, Stemphylium consistently infected familiar hosts more frequently, while causing less damage on them. This pattern is consistent with the hypothesis of adaptive evolution in both the pathogen (ability to infect) and the host (tolerance of infection). Together these results suggest the potential for rapid evolution to alter interactions between plant invaders and their natural enemies.

Since 2004, a new leaf blight disease on garlic of high severity has been observed in Dangyang County, Hubei province, China. Initial symptoms consisted of multiple, small, irregular to oval, white leaf spots, which enlarge to produce sunken purple lesions, sometimes surrounded by a bright yellow margin. As the disease progressed, lesions expanded and merged, resulting in withering of leaf tips. After isolation and pathogenicity testing, the causal agent of leaf blight of garlic was identified as Stemphylium solani from cultural and morphological characteristics, and subsequent analysis of the internal transcribed spacer region of ribosomal DNA. When fungal plugs of two S. solani isolates were inoculated onto 11 garlic cultivars and 20 other crop species, leaf spots appeared on all inoculated plants, but two garlic cultivars (Qingganruanye and Ruanruanye) and three crop species (Capsicum annuum, Brassica napus and Amaranthus mangostanus) showed the smallest leaf spots. In cross-inoculation experiments, no indications of host specificity were observed, but S. solani isolated from garlic was generally the most virulent on five plant species, while the isolate from leek (Allium odorum) was generally the least virulent. Toxicity testing of the crude culture filtrates indicated that garlic isolates produced toxin(s) that were not heat-labile and induced different levels of phytotoxicity toward various garlic cultivars and crops.