Differences in response to the toxin sirodesmin PL produced by Phoma lingam (Tode ex fr.) Desm. on protoplasts,cell aggregates and intact plants of resistant and susceptible Brassica accessions

Summary The selective property of sirodesmin PL, a toxin produced by Phoma lingam, was studied on protoplasts, cell aggregates, leaves and roots. Directly after isolation, protoplasts from all the different Brassica accessions were sensitive when treated with toxin in a concentration higher than 1 M. When more differentiated plant tissue. i.e. cell aggregates, leaves or roots, were investigated, insensitivity to the toxin was found in the plant material resistant to P. lingam, while the plant material susceptible to P. lingam was sensitive. The results reveal that a clear correlation between resistance to P. lingam and insensitivity to sirodesmin PL is present, and that the toxin can be used to distinguish resistant plant material from susceptible both in vivo and in vitro.     

Inter-relationship between shoot weight,severity of root rot and survival rate of subterranean clover inoculated with certain pathogenic fungi

Summary Plant survival rate, root disease index and fresh shoot weight of subterranean clover seedlings inoculated with fungal pathogens (Fusarium avenaceum, F. oxysporum, Phoma medicaginis, Pythium irregulare andRhizoctonia solani, both singly and in combinations) were generally inter-correlated over a wide range of temperature (10, 15, 20 and 25°C) and moisture conditions (45, 65% water holding capacity and flooding). There was a negative correlation between root disease index and shoot weight for all treatments exceptF. avenaceum + P. irregulare. Root disease index and seedling survival rate were negatively correlated except forF. oxygsporum, Phoma medicaginis, P. irregulare andF. oxysporum + F. avenaceum. However, a good positive correlation was found between the survival rate and shoot weight for all treatments with the exception ofPhoma medicaginis.     

Screening biological activities of soil-borne Streptomyces sp. against several phytopathogenic fungi

About 70 Streptomyces species, isolated from soils of greenhouses and citrus orchards were evaluated for their antagonistic activity against Verticillium dahliae, Fusarium subglutinans, Fusarium sambucinum, Phoma glomerata and Nattrassia mangiferae. Preliminary screening for antimicrobial activity was determined by dual culture method. The soils of Kerman are rich sources of micro-organisms with potent biological activities, and screening programmes are to be conducted to reveal the presence of active Actinomycetes isolates against phytopathogenic fungi.     

Phytoalexins from Thlaspi arvense, a wild crucifer resistant to virulent Leptosphaeria maculans: structures, syntheses and antifungal activity

Phytoalexins are inducible chemical defenses produced by plants in response to diverse forms of stress, including microbial attack. Our search for phytoalexins from cruciferous plants resistant to economically important fungal diseases led us to examine stinkweed or pennycress (Thlaspi arvense), a potential source of disease resistance to blackleg. We have investigated phytoalexin production in leaves of T. arvense under abiotic (copper chloride) and biotic elicitation by Leptosphaeria maculans (Desm.) Ces. et de Not. [asexual stage Phoma lingam (Tode ex Fr.) Desm.], and report here two phytoalexins, wasalexin A and arvelexin (4-methoxyindolyl-3-acetonitrile), their syntheses and antifungal activity against isolates of P. lingam/L. maculans, as well as the isolation of isovitexin, a constitutive glycosyl flavonoid of stinkweed, having antioxidant properties but devoid of antifungal activity.     

Phomapyrones from blackleg causing phytopathogenic fungi: isolation, structure determination, biosyntheses and biological activity

The isolation and structure determination of phomapyrones D-G, three 2-pyrones and a coumarin, from a group of isolates of the fungal pathogen Leptosphaeria maculans (Desm.) Ces. et de Not., asexual stage Phoma lingam (Tode ex Fr.) Desm, is reported. As well, phomenin B, infectopyrone, and polanrazines B and C were also obtained for the first time from these isolates. In addition, based on results of incorporations of 13C-labeled acetate and malonate, and deuterated methionine, a polyketide pathway is proposed for the biosyntheses of phomapyrones.     

Biological and genetic characterisation of Phoma macrostoma isolates with bioherbicidal activity

The fungus Phoma macrostoma Mont. isolate 94-44B was registered as a bioherbicide for control of broadleaved weeds in Canada and the USA in 2011 and 2012, respectively. To obtain the registrations, the fungus had to be characterised both biologically and genetically. The objectives of this study were to demonstrate that bioherbicidal activity was associated with specific genetic markers and to determine whether bioherbicidal activity was a general trait of the species or only selected isolates. A collection of 64 isolates of P. macrostoma was established. A greenhouse bioassay and bioherbicidal-specific primers were used to determine bioherbicidal activity of all isolates. Only isolates originating from Canada thistle demonstrated the ability to reduce dandelion seedlings and display the 853 bp amplicon for the bioherbicidal-specific primer. Bioherbicidal isolates were consistently differentiated from all other isolates with two main genotypic groupings (I and II) arising from internal transcribed spacer (ITS) and amplified fragment length polymorphisms (AFLP) sequence analyses. Using AFLP, two biotypes of bioherbicidal isolates were also differentiated by the presence or absence of an AFLP marker at a single polymorphic locus. The genetic divergence among the bioherbicidal and nonbioherbicidal isolates of P. macrostoma was only 2.21% which was lower than that reported for other related Phoma sp. Other than the bioherbicidal trait, there was no apparent affiliation of the genetics with known varietal types, host or geographic origin. ITS sequence analysis and AFLP fingerprinting may be used as tools to detect bioherbicidal isolates of P. macrostoma.     

Effectiveness of acibenzolar-S-methyl, fungicides and antibiotics for the control of brown eye spot, bacterial blight, brown leaf spot and coffee rust in coffee

This study was carried out to evaluate the potential of acibenzolar‐S‐methyl (ASM), combined or not combined with fungicides and antibiotics for the control of brown eye spot (Cercospora coffeicola) and bacterial blight (Pseudomonas syringae pv. garcae) in coffee seedlings, and ASM combined with conventional fungicide application schedules for the control of coffee rust (Hemileia vastatrix) and brown leaf spot (Phoma costarricencis) under field conditions in two coffee crops in the State of São Paulo, Brazil. ASM protected coffee seedlings against C. coffeicola when applied at the rates of 2.5 and 5 g of active ingredient per hectolitre of water (g a.i. hL^?1), providing 34–55% of disease control, and against bacterial blight, when applied at the rates of 2.5, 10 and 20 g a.i. hL^?1, with 38–57% of disease control. Tebuconazole (100 g a.i. hL^?1) and azoxystrobin (10 g a.i. hL^?1) showed the best results for brown eye spot control. Oxytetracycline + streptomycin, kasugamycin hydrochloride, oxytetracycline + metallic copper, copper oxychloride and mancozeb + copper oxychloride also controlled bacterial blight in levels similar to those shown by ASM. In the field experiments, all fungicide application schedules tested, cyproconazole (December, February, April), epoxiconazole (December, March), tetraconazole (December, February, April), cyproconazole (December, February) and azoxystrobin (January, March) were effective for coffee rust control and provided partial control of brown leaf spot. The results also showed that for all experiments, there was no synergistic effect of the combination of ASM with azoxystrobin, cyproconazole or cupric fungicides.     

Presence of Leptosphaeria maculans Group A and Group B Isolates in Sweden

Leptosphaeria maculans isolates have been assigned to one of two groups, A or B, on the basis of differences in their characteristics. Group A can further be divided into pathogenicity groups (PG) 2, 3 and 4 and group B into PG1. To determine if isolates belonging to the aggressive canker forming group A are present in Sweden, physiological and genetic characterisation of 120 isolates collected in the year 2000 were performed. Thirty‐seven isolates were classified as belonging to pathogenicity group PG3 and 63 isolates as PG4, based on a cotyledon assay. Twenty isolates did not cause any symptoms at all, and were classified as PG1. When comparing two geographical regions, Skåne and Östergötland, equal numbers of PG3 and PG4 isolates were found. By analysing the isolates by PCR, the collection was further classified into 100 group A isolates and 20 group B isolates. A corresponding classification of the isolates was observed when the ability to produce pigments in Czapek Dox broth was examined. The results showed a clear predominance of group A. This was also the case for the isolate collection from 2001. In a detailed survey of disease development in a L. maculans infected winter oilseed rape field in southern Sweden (Skåne), basal stem canker was not observed until early June Although the disease index value increased from 8.4 in June to 18.0 in July, few severely damaged plants were observed before harvest in mid‐July, despite infection with group A isolates.     

Extracellular lipolytic activity in Phoma glomerata

Several properties of the lipolytic activity exhibited by the conidial fungus Phoma glomerata were studied. Lipolytic activity in an aqueous buffer medium was measured on triacylglycerol, phosphoglyceride and cholesterol ester under different experimental conditions. The effect of storage temperature on the stability of the hydrolytic activity, and optimal conditions of temperature and time of maximal activity were determined. The optimal conditions for maximal lipolytic activity were found to be 40–50 °C and 1 h. The activity released to the medium by 1 mg cells for 1 h at 40 °C was stated as the enzyme released unit (ERU). The protein fraction of MW > 50 kDa obtained by ultrafiltration of the medium, was active on the three substrates assayed, and it showed a non-specific hydrolytic activity on both the 1- and 2-acyl esters either in the neutral glyceride or in the phosphoglyceride. A protein of M _r approx. 75 kDa was the only one that showed esterase activity. The crude medium, stored at –15 °C, maintained its initial hydrolytic activity on triacylglycerol for at least 42 days, though when it was kept for 10 days at 4 °C, the activity fell to 50%. Kinetic parameters using substrates such as triolein (TO), dipalmitoyl phosphatidylcholine (DPPC) and cholesteryl oleate (ChoO), were comparatively evaluated. The activity of the enzyme in the hydrolysis of TO showed the highest values, whereas the maximal specific activities were less when the enzyme was assayed against DPPC and ChoO.