Phoma Exigua Research Articles

Sulphur dioxide effects on fungi growing on leaf litter and agar media

summaryRespiration of four decomposer fungi (Mycena galopus (Pers.) Kutnmer, Aureobasidium pullulans (de Bary) Arnaud, Phoma exigua Desm. and Cladosporium cladosporioides (Fres.) de Vries) growing on four species of leaf litter (Pinus sylvestris L., Picea sitchensis (Bongard) Carriére, Fraxinus excelsior L. and Corylus avellana L.) was inhibited by dry‐deposited SO2 in a laboratory experiment. Mycelial extension of the four fungi growing on four different agar media was inhibited by SO3 fumigation (40 nl l−1) in the laboratory, and media containing carbohydrates decreased the inhibitory effect of SO2 fumigation. Fumigation caused a statistically significant reduction in the mycelial extension of all species tested on tap‐water agar. These experiments demonstrate that decomposition of leaf litter is inhibited by environmentally realistic concentrations of SO2 and that the effect is exerted via inhibition of saprotrophic fungi.

Cytochalasin W, a new 24-oxa[14]cytochalasan from Phoma exigua var. heteromorpha.

A further cytochalasin was isolated from liquid culture filtrates of Phoma exigua var. heteromorpha together with cytochalasins U and V and other well-known cytochalasins. The metabolite, named cytochalasin W, was characterized by spectroscopic and chemical methods as a new 24-oxa[14]cytochalasan, bearing a formyl group on the macrocyclic ring. Cytochalasin W showed toxic activity in the brine shrimp assay.

The use of carvone in agriculture: sprout suppression of potatoes and antifungal activity against potato tuber and other plant diseases

Carvone (derived from caraway seed), previously identified as an effective potato sprout inhibitor, was examined under semi-practical storage conditions and compared with commonly used propham/chlorpropham (IPC/CIPC) mixtures. Carvone administered at regular intervals during long-term storage was able to control sprout growth equally well or more effectively than IPC/CIPC mixtures. Furthermore, carvone showed antifungal activity against various fungal diseases in in-vitro experiments. In in-situ experiments, promising antifungal activity was obtained against the potato storage diseases Fusarium sulphureum, Phoma exigua var. foveata and Helminthosporium solani. Carvone was recently launched as a sprout inhibitor for potatoes in the Netherlands under the trade name “Talent”.

Effectiveness of Selected Fungicides in Controlling Foliar Diseases of Common Periwinkle (Vinca minor L.)

Common periwinkle and `Bowles' periwinkle production has declined in the southern United States due to foliar diseases caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. and Phoma exigua Desmaz. var. inoxydabilis Boerema & Vegh in Vegh et al. Our study determined whether several labeled and experimental fungicides could control pathogens causing foliar diseases in common periwinkle in vitro and outdoors during two consecutive summers. Five concentrations of each of eight fungicides were used to test inhibition of mycelial growth of P. exigua var. inoxydabilis and two isolates of C. gloeosporioides on fungicide-amended agar. All concentrations of propiconazole inhibited growth of P. exigua var. inoxydabilis (100%) and both isolates of C. gloeosporioides (>96%). Cyproconazole completely inhibited mycelial growth of P. exigua var. inoxydabilis. Thiophanate methyl/mancozeb partially inhibited growth of C. gloeosporioides (50%). In outdoor trials, plants were sprayed weekly with the following fungicides and rates (in g a.i./liter): thiophanate methyl/mancozeb, 1.35; propiconazole, 0.14; thiophanate methyl, 0.84; triforine, 0.27; cyproconazole, 0.08; triforine–CC 17461, 0.27; or CGA 173506, 0.90. Thiophanate methyl/mancozeb was most effective at reducing foliar necrosis during both seasons. Shoot dry weights of plants treated with thiophanate methyl/mancozeb were significantly higher at the end of each growing season than those of plants treated with the other fungicides or the nontreated control plants. Chemical names used: dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] and a combination of zinc ion and manganese ethylenebisdithiocarbamate (thiophanate methyl/mancozeb); 1-[2-(2′,4′-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl-methyl]-1H-1,2,4-triazole (propiconazole); dimethyl [(1,2-phenylene)-bis (iminocarbonothioyl)] bis [carbamate] (thiophanate methyl); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] (triforine); 2-(4-chlorophenyl)-1-(1H-1,2,4-triazol-l-yl)-butan-2-ol (cyproconazole); N,N′-[1,4-piperazinediylbis (2,2,2-trichloroethylidene)] bis [formamide] with micro emulsion (triforine–CC 17461); 4-(2-2-difluoro-1,3-benzodioxol-4-yl) pyrrole-3-carbonitrile (CGA 173506).

Process for the production and purification of cytochalasin B fromPhoma exigua var.heteromorpha

A patented process to produce and purify large amounts of cytochalasin B is described. The fungal microorganism,Phoma exigua var.heteromorpha, is grown on a solid medium, constituted by autoclaved wheat kernels. The fungal culture, obtained growing the fungus in optimized environmental conditions, is extracted by organic solvent, to obtain crystalline cytochalasin B, in more than 3 g/kg of dried wheat culture. The advantages of this process are: production higher than that obtained with other known processes; lower production expenses; lower quantities of solvents; exclusion of Chromatographic purifications. Moreover, the production of large amounts of cytochalasin B allow to prepare a wide number of derivatives, with different biological activities.

Control of Phoma exigua var. linicola on flax by seed and foliar spray treatments with fungicides

In order to define a strategy for the chemical control of Phoma exigua var. linicola, experiments on seed and foliar spray treatments with fungicides were conducted in 1990 and 1991 in the field. The results showed that seed treatments (difenoconazole, prochloraz, flusilazol plus tridemorph) did not succeed in reducing the incidence of the foot rot disease of flax when an aerial infection occurred at an early stage of plant development; under these circumstances, therefore, seed treatments must be supplemented with spray treatments. In both years, one foliar spray treatment with prochloraz tended to decrease the percentage of disease. In 1991, difenoconazole, and flusilazol plus tridemorph, were tested and proved more effective than prochloraz. The efficiency of these fungicides was greatest when applied soon after inoculation, rather than closer to harvest.

A 9-year monitoring study of diseases on potato seed tubers imported to Israel

Potato seed tubers are imported annually to Israel from northern Europe. Although the seed is registered as certified, a survey carried out over a 9-year period indicated that most lots were affected by latent or active bacterial and fungal infections. Latent infection byErwinia carotovora subsp.atroseptica, the causal agent of blackleg, at a level of 103 cells/g peel, was present in 30% of the lots in most years. Black scurf caused byRhizoctonia solani was present in 20–70% of the imported lots, with a moderate to high level of infection in all years except 1985. In contrast, although many lots were affected by powdery scab, common scab, and Fusarium dry rot in most years, disease incidence within lots was generally low. The gangrene pathogen (Phoma exigua) was rarely detected. The survey findings are of marked importance, due to the extensive use of soil fumigation in Israeli agriculture.

The effect of collembolan grazing on fungal activity in differently managed upland pastures: A microcosm study

Laboratory microcosms containing litter from three tussock grasslands were used to assess the impact of grazing by a collembolan, Onychiurus procampatus, on the abundance, nutrient release, and respiration of the saprotrophic fungus, Phoma exigua. The fungal biomass and respiration rate were significantly reduced only when Collembola were present in excess of mean field densities but perhaps more typical of spatial aggregations in the soil. A high efficiency of nutrient immobilization by P. exigua was demonstrated but nutrient release was not significantly affected by the fauna. Problems associated with the use of microcosms in the simulation of field conditions are discussed.

FOLIAR DISEASES OF THE GROUND COVER, VINCA MINOR L., DURING NURSERY PRODUCTION

The production of Vinca minor, a shade tolerant ground cover, has declined in recent years due to foliar diseases. Two fungal pathogens, Colletotrichum gloeosporioides and Phoma exigua var. inoxydabilis, were consistently observed on infected plant material from Oklahoma nurseries. Symptoms caused by C. gloeosporioides included severe anthracnose and stem dieback, while P. exigua caused leaf and stem lesions. The pathogenicity of two isolates of C. gloeosporioides and one isolate of P. exigua was evaluated on the native species and the cultivar `Bowles' of V. minor to determine relative disease resistance of these plants. Specific environmental conditions for infection were determined by C. gloeosporioides. Infection was greatest at 28±1°C with high humidity and a light intensity of 126 μmol m-2-sec-1. Five concentrations of eight fungicides (chlorothalonil, cupric hydroxide, mancozeb. propiconazole, San 619, thiophanate methyl, thiophanate methyl/mancozeb, and triforine) were used to test mycelial growth inhibition of the three isolates on amended agar. San 619 completely inhibited mycelial growth of P. exigua, and propiconazole inhibited growth of all three isolates at all concentrations tested.

Heritability and Sources of Ascochyta Blight Resistance in Common Bean

Common bean germ plasm (Phaseolus vulgaris) with intermediate Ascochyta blight (caused by Phoma exigua var. diversispora) resistance has been identified at CIAT. The heritability and inheritance of resistance to this pathogen were studied in three resistant climbing bean sources. Narrow-sense heritability estimates determined by the regression of the F 2 -derived F 4 line means on F 2 -derived F 3 line means from crosses Carioca (S)×G 10817 (R) and G 10088 (S)×G 10747 (R) were low to moderate (0.19-0.64), depending on the cross and character measured

Seed treatments increase yield of farmer varietal field bean mixtures in the central African highlands through multiple disease and beanfly control

Seed treatments with fungicides to control seed-borne and root diseases of Phaseolus vulgaris and their use with an insecticide treatment to control beanfly ( Ophiomyia spencerella), were evaluated in diverse regions of Rwanda. Benomyl reduced the severity of diseases caused by Colletotrichum lindemuthianum, Phaeoisariopsis griseola and Phoma exigua var. diversispora. Multiregional multiseasonal on-farm trials using benomyl, thiram and the insecticide endosulfan, reduced the severity of seed-borne diseases and beanfly and increased yields of diverse varietal bean mixtures by 25% in regions above 1400 m in elevation. Combined treatments increased bean yields 17% and 35%, respectively, in the September and March seasons. Seed treatments with endosulfan alone increased yields by 17% in multiseasonal multiregional trials, through yield increases in the March season, but not in the September season, owing to low beanfly pressure. Yield increases from endosulfan applications alone occurred in regions below an elevation of 1700 m. A presowing seed treatment of benomyl, thiram and endosulfan was effective over the broadest range of conditions. Seed treatments can reduce farmers' risk of damage from multiple diseases and beanfly, thus substantially increasing on-farm bean productivity; they are effective without promoting genetic erosion of the diverse bean varietal mixtures used by local farmers in the Great Lakes region of Africa, as can occur with genetic replacement strategies.

Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter I. Changes in communities of fungal saprotrophs.

Comparisons of the saprotrophic fungi isolated from ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), pedunculate oak (Quercus robur L.), sessile oak [Q. petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from three woodlands exposed to low, medium and high levels (c. 0.0→ 0.060μl l-1 ) of sulphur dioxide (SO2 ) showed that the composition of the fungal communities differed between sites. Fumigation of angiosperm tree leaf litters from the least and the most polluted site with environmentally-realistic concentrations (0.010-0.030 μl1 ) of SO2 for 16-68 wk in an open-air field-fumigation experiment resulted in marked changes in the composition of the fungal communities in the leaf litters, comparable with differences found between the woodland sites. Cladosporium spp., Epicoccutn nigrum Link, Fitsarium spp. and Phoma exigua Desm. were less commonly isolated from leaf litters exposed to SO2 , whereas Coniothyrium quercinum Sacc. var. glandicola Grove, Cylindrocarpon orthosporum (Sacc.) Wollenw. and Penicillium spp. were more frequently isolated from fumigated litters. However, few differences could be detected in the response to SO2 of the mycofloras of leaf litters originating from different woodland sites. In general, SO2 did not affect the total extent of fungal occupancy of the microsites in the litter, as fungal species which decreased in abundance on exposure to the gas appeared to be replaced in the litter by other species more tolerant to the gas. SO2 therefore appeared to be selectively toxic to saprotrophic fungi isolated from these litters.

Effects of dry-deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter III. Decomposition rates and fungal respiration.

Ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), sessile oak [Quercus petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from a virtually non-polluted and a heavily sulphur dioxide (SO2 )-polluted woodland were fumigated with environmentally-realistic concentrations (0.010-0.030μl l-1 ) of SO2 for 16-68 wk in an open-air field-fumigation experiment. Fumigation inhibited the respiration (CO2 evolution) and decomposition rates of the leaf litters. However, there were few differences in the responses between leaf litters from the two woodlands. In addition, pure cultures of four saprotrophic fungi were grown individually on irradiated hazel litter and exposed to c. 0.030μl l-1 of gaseous SO2 , for 28 d in the laboratory. The gas inhibited the respiration of Phoma exigua Desm. and Phoma macrostoma Mont, but not the respiration of Cladosporium cladosporioides (Fres.) de Vries or Coniothyrium quercinum Sacc. var. glandicola Grove. These results in part substantiated findings of previous experiments examining the effects of SO2 on the structures of saprotrophic fungal communities. The effects of SO2 on fungal decomposition of angiosperm tree leaf litter as possible causes of forest decline are discussed.

Invasion of rust ( Puccinia poarum) pycnia and aecia on coltsfoot ( Tussilago farfara) by secondary pathogens: death of host leaves

Necrotrophic fungi were cultured after isolation from rust (Puccinia poarum) pustules on leaves of Tussilago farfara, collected in the field. Healthy and rusted (P. poarum) leaves of T. farfara were re-inoculated in a greenhouse with these potential secondary invaders and development of necrosis and death of leaves was determined. Alternaria alternata, Fusarium sp., Phoma exigua and Phoma glomerata caused formation of necrotic tissue and (non-systemic) death of leaves, whereas leaves inoculated with Cladosporium herbarum and Epicoccum nigrum were similar to leaves inoculated with sterile water. Greater necrosis developed when aecia rather than pycnia were inoculated and at both stages secondary damage increased with increasing pustule density. Comparison with other host-rust systems and aspects of biological weed control are discussed.

Perspectives of green-crop-harvesting to control soil-borne and storage diseases of seed potatoes

An overview is given on the history of vine killing meant to reduce virus transmission to potato seed tubers. With mechanical harvesting, problems arise with respect to skin damage and pathogens, which strongly develop on the decaying vines and roots, such asRhizoctonia solani, Phoma exigua var.foveata andErwinia spp. Green-crop-harvesting (GCH), a recently developed fully mechanical vine killing method, is marked by vine destruction, lifting tubers, placing them on a soil bed followed by covering them with soil and an in situ healing period of at least ten days in the newly formed ridges.

Physiological characterization of opine-utilizing rhizobacteria for traits related to plant growth-promoting activity

Thirty-two strains of opine-utilizing rhizobacteria were evaluated for physiological traits which have been related to plant growth-promoting activity. Tests included antibiosis against two bacterial and eight fungal pathogens of potato (Solanum tuberosum L.), production of hydrogen cyanide and fluorescent pigment production. On average, 71 and 12% of the bacteria inhibited the growth of Erwinia carotovora subsp. carotovora and Agrobacterium tumefaciens, respectively. The growth of Botrytis sp. was inhibited by 62% of the bacteria, and half of these produced an inhibition zone of more than 7 mm in diameter. Fusarium solani, Colletotrichum coccodes, Phoma exigua, Verticillium dahliae, F. oxysporum, V. albo-atrum and F. sambucinum were antagonized by 43, 34, 31, 25, 19, 18, and 12% of the bacteria, respectively. Only four strains produce hydrogen cyanide. The inhibition of a plant pathogen was not correlated to the production of fluorescent pigment. No strain produced a hypersensitive reaction whereas only three strains induced soft-rot and two produced polygalacturonase. Some opine-utilizing rhizobacteria were strong inhibitors of all plant pathogens, while most were active against specific plant pathogens.

Cytochalasins from Phoma exigua var. Heteromorpha

Three further cytochalasins from Phoma exigua var. heteromorpha, grown on wheat, were isolated and characterized by spectroscopic methods and by chemical correlation with cytochalasin B. They were identified as cytochalasin T, a new 24-oxa[14]cytochalasan, cytochalasin F and 7- O-acetylcytochalasin B, both isolated for the first time from this fungus. Cytochalasin F showed significant activity in the brine shrimp assay and on tomato seedling growth.

Fungicide Treatments for the Control of Storage Rots of Seed Potatoes.

Five fungicides were compared with a standard mercuric fungicide for the control of gangrene and Fusarium dry rot of seed potatoes. Seed tubers were artificially wounded and inoculated with Phoma exigua var. foveata and/or Fusarium trichothecioides before dipping in suspensions of the test fungicides. All of the six fungicides tested on tubers infected with P. exigua var. foveata reduced gangrene significantly. Of the three most effective materials, viz, thiabendazole, imazalil and prochloraz, imazalil proved to be the best for the control of gangrene. Combining imazalil with either thiabendazole or prochloraz did not improve control. Of the fungicides tested, thiabendazole gave the best control of dry rot, caused by F. trichothecioides. However, control was improved by combining this fungicide with prochloraz and imazalil.

Effects of temperature on growth rates of fungi from subantarctic Macquarie Island and Casey, Antarctica

The linear growth rates of fungal isolates were measured on agar plates at temperatures ranging from 4° to 35°C. Fungi tested included the major fungal colonizers of leaves and litter of the three dominant plant species on subantarctic Macquarie Island, and major fungal species associated with plant and soil communities near Australia's Casey Station on the Antarctic Continent. All fungi grew at 4°C and were classified as psychrotrophs. Maximum growth rates were recorded at temperatures of 10° to 20°C for 13 of the 15 isolates from Macquarie Island and for all six isolates from Casey. Most of the leaf colonizing fungi from Macquarie Island had optimum growth temperatures of 15°C whereas all litter fungi from Macquarie Island and Casey fungi except Thelebolus microsporus had optimum growth temperatures of 20°C or above. Maximum growth of all species was at temperatures above those normally prevailing in their natural environments, with most species growing at 4°C at between 10% and 30% of their maximum rates. However, microclimatic effects may have resulted at times in temperatures near their growth optima. The highest growth rates at 4°C were recorded for Phoma spp. 1 and 2, Phoma exigua and Mortierella gamsii from Macquarie Island and Mortierella sp. 1 from Casey. Thelebolus microsporus and sterile sp. G from Casey also grew relatively fast at 4°C, and these species, and Phoma sp. 3 and Phoma exigua from Macquarie Island had the lowest Q-10 values for the temperature range 4° to 15°C.

Effect of haulm treatment and harvest time on incidence of tuber rots of potato (Solanum tuberosum L.) after standard wounding and on frequency of stem lesions caused byPhoma foveata Foister

Various haulm treatments and harvest times differentially influenced the incidence of storage rots in potato tubers (Solanum tuberosum L.) in field experiments in Sweden performed over 4 years. The incidence of gangrene caused byPhoma foveata Foister (Phoma exigua var.foveata (Foister) Boerema) increased in cv. Bellona after spraying haulms with diquat as did the amount of infection caused byFusarium avenaceum (Corda ex. Fr.) Sacc. in all three cultivars (Bintje, Bellona, and Magnum Bonum). The lowestP. foveata infection levels occurred after pulling haulms. Late harvesting increased the frequency ofP. foveata in cvs Bintje and Bellona both at 2 and 4 wks interval between haulm treatment and harvest. Tuber and visible stem infection caused byP. foveata were correlated for cvs Bintje and Bellona, but not for cv. Magnum Bonum. The possible relation between tuber and stem infection is discussed.