Plectosphaerella Cucumerina Research Articles

Potential of an Indigenous Fungus, Plectosporium tabacinum, as a Mycoherbicide for Control of Arrowhead (Sagittaria trifolia).

An isolate of the indigenous fungus Plectosporium tabacinum was isolated from arrowhead (Sagittaria trifolia) in Yusung, Korea in 1990 and evaluated in laboratory and growth chamber tests as a potential mycoherbicide. The fungus grew comparatively slowly on potato dextrose agar and corn meal agar, attaining a diameter of 65 mm after 12 days at 25°C. Conidia were mass-produced in shake-cultures or in a fermentor using potato dextrose broth containing yeast extract (0.5%, wt/vol) at 25°C. When arrowhead seedlings at the 2- to 3-leaf stage were inoculated with conidial suspensions (2 × 107 conidia/ml) and incubated in a dew chamber for 18 h at 25°C, the plants developed small, brown spots on the leaves and petioles in 2 days, and were blighted completely within 7 days after inoculation. This effect was consistent on arrowhead plants from the 2- to 5-leaf stage. Another arrowhead species, S. pygmaea, was as susceptible as S. trifolia to the pathogen. Several crops, including rice, barley, and wheat and 34 other common weed species, were immune. In small-scale field tests in paddy fields during the summers of 1992 and 1993, a mean reduction of 71.3% in the number of arrowhead plants was observed following a foliar spray of a conidial suspension (107 conidia/ml). These results indicate that P. tabacinum has potential as a selective mycoherbicide for arrowhead control.

Occurrence of Vine Decline Diseases of Muskmelon in Guatemala.

Central American countries have become major production areas of melons (Cucumis melo L.) destined for export to Europe and the United States during the winter months. Double cropping in the same fields year after year has created serious vine decline diseases in melons grown in the Capco area of Guatemala. Vines typically appear healthy until the fruit are approaching maturity, when the crown leaves begin to turn yellow and collapse and the decline gradually radiates outward. There was evidence of slightly water-soaked lesions in the crown of some plants; however, the symptoms were not similar to charcoal rot or gummy stem blight. The roots exhibited some decay, lesions, and discoloration, but were not macerated and rotten. A minimum of 10 affected plants were collected from each of nine fields in the Capco area of Guatemala. Isolations were made from the crown area, primary root, and secondary roots of selected plants by excising 3- to 5-mm pieces and surface sterilizing them for 30 to 60 s with 0.5% sodium hypochlorite. The isolations were made on 2% water agar plus 0.1 g of streptomycin sulfate per liter. Plates were examined for fungal growth daily for 5 days with hyphal tips from all colonies transferred to potato dextrose agar and Synthetischer nährstoffärmer agar (2) and allowed to sporulate. Isolations revealed the presence of several fungi capable of causing vine decline or suspected of being involved in the vine decline complex. Rhizoctonia solani Kühn and Fusarium semitectum Berk. & Ravenel were isolated from more than 50% of plants in some fields. F. semitectum, R. solani, and a Stagonospora-like fungus were isolated from 38, 18, and 17% of the total plants, respectively. R. solani was isolated from the crown more often than from the roots, but its role is not understood. With one exception, F. semitectum was always isolated from the crown area, which may suggest a more significant role in the vine decline complex than suspected previously. The Stagonospora-like fungus, isolated from 30% of the plants from one field, has been reported as a pathogen of cantaloupe that may contribute to the vine decline complex (1). Monosporascus cannonballus Pollack & Uecker and Fusarium oxysporum Schlechtend.:Fr. emend. W. C. Snyder & H. N. Hans. were isolated from 60% of the plants from one field. It was the only field in which M. cannonballus was isolated. Plectosporium tabacinum (van Beyma) M. E. Palm, W. Gams et Nirenberg, a cucurbit pathogen, was isolated infrequently. This is the first report of M. cannonballus, P. tabacinum, and the Stagonospora-like fungus in Guatemala.

Fusarium solani on Soybean Roots: Nomenclature of the Causal Agent of Sudden Death Syndrome and Identity and Relevance of F. solani form B.

Two morphological forms of Fusarium solani pathogenic on soybean, forms A and B, were further characterized and distinguished from other fungi. Questions regarding their identity were addressed. Soybean plants grown in the field and in a growth chamber were inoculated with Fusarium solani form A and F. solani f. sp. phaseoli. F. solani form A incited leaf symptoms typical of sudden death syndrome; F. solani f. sp. phaseoli did not. It was concluded that the two fungi are different and distinguishable on the basis of host specialization and the types of symptoms they incite on soybean. F. solani form A, the causal agent of sudden death syndrome, was designated F. solani (Mart.) Sacc. f. sp. glycines form. nov. Cultural and morphological characteristics of F. solani form B, the cause of seedling disease and root rot of soybean, and Plectosphaerella cucumerina were compared to determine the validity of a report indicating that they were conspecific. Results demonstrated that F. solani form B and P. cucumerina are distinctly different and not conspecific. The relevance of identifying and recognizing the two F. solani forms as separate and distinct members of the F. solani pathogen complex on soybean is discussed.

Plectosporium, a new genus for Fusarium, tabacinum, the anamorph of Plectosphaerella cucumerina

AbstractPlectosporium is described as a new genus for Fusarium tabacinum (≡ Cephalosporium tabacinum), the anamorph of Plectosphaerella cucumerina. The genus is characterized by moist colonies, sim...

Plectosporium, a New Genus for Fusarium tabacinum, the Anamorph of Plectosphaerella cucumerina

Plectosporium is described as a new genus for Fusarium tabacinum (≡ Cephalosporium tabacinum), the anamorph of Plectosphaerella cucumerina. The genus is characterized by moist colonies, simple or branched conidiophores, apical or lateral phialides that sometimes proliferate percurrently or have more than one conidiogenous locus, with a cylindrical collarette and sometimes with a sinuous apex, bilaterally symmetric, hyaline, 0- to 1-septate conidia that often appear slightly curved in side view, and sometimes a Plectosphaerella teleomorph.

Phylogenetic relationships of the soybean sudden death syndrome pathogen Fusarium solani f. sp. phaseoli inferred from rDNA sequence data and PCR primers for its identification.

Phylogenetic relationships of several species within the Fusarium solani-complex were investigated using characters from the nuclear ribosomal DNA. Genetic variation within 24 isolates, including 5 soybean sudden death syndrome (SDS) strains, was assessed using rDNA sequence data and restriction fragment length polymorphic markers. By these techniques, the causal agent of soybean SDS was identified as F. solani f. sp. phaseoli. In separate cladistic analyses, Plectosphaerella cucumerina and Nectria cinnabarina or F. ventricosum were used for rooting purposes. Monophyly of the F. solani-complex was strongly supported by bootstrap and decay analyses. Parsimony analysis indicates that this complex is composed of a number of phylogenetically distinct species, including Neocosmospora vasinfecta, F. solani f. sp. phaseoli, and biological species designated as MPI, MPV, and MPVI of N. haematococca. The results demonstrate complete congruence between biological and phylogenetic species within the N. haematococca-complex. In addition, DNA sequence data were used to design a PCR primer pair which could specifically amplify DNA from isolates of the SDS pathogen from infected plants.

Effect of substrate and plant maturity on the incidence of infection of potato roots by pathogenic and non-pathogenic fungi

Colonization of roots of field-grown potato plants by pathogenic and non-pathogenic fungi was examined by plating surface-sterilized roots onto low nutrient medium. Plants which originated from micropropagated nodal cuttings (MP plants) or from seed-grade potato tubers (ST plants) were subjected to nine pre-plant treatments designed to test the effect of different potting substrates and different levels of natural tuber inoculum on the root mycoflora. The experiment was repeated in a second year but at a different site; in each year roots were collected once in July, August and September. Cylindrocarpon destructans, Colletotrichum coccodes, Trichoderma viride, Microdochium bolleyi and Fusarium tabacinum showed the highest mean frequencies of colonization; Verticillium tricorpus, Rhizoctonia solani, Polyscytalum pustulans and Gliocladium roseum were mainly confined to roots of ST plants or MP plants with added tuber inoculum, and Trichoderma viride, Chrysosporium pannorum, Penicillium spp., Aureobasidium pullulans and Phoma leveillei were dominant in roots of MP plants raised in peat-based potting substrates. There was evidence of suppression of the potato pathogens R. solani, P. pustulans and C. coccodes, and of several non-pathogens in roots of the same plants. Most of the fungi recovered from potato roots were also typical components of the soil microflora and occurred in both field sites. Exceptions were Fusarium oxysporum and V. dahliae, which were found in one year only. Possible associations and dissociations between different combinations of fungi occurring together on the same root system were evaluated using a correlation matrix, and spatial relationships of different groups demonstrated by principal coordinate analysis. The influence of the indigenous mycoflora on root colonization by particular potato tuber pathogens is discussed.

Development and Cytology of Plectosphaerella Cucumerina

Development of the ascoma of Plectosphaerella cucumerina begins with the formation of a coiled ascogonium that becomes surrounded by branches from the parent hypha or from neighboring hyphae or both. Paraphyses develop as rows of cells with the lower ones laterally expanded to form an apparent pseudoparenchyma. Apical meristematic cells of the ascoma grow upward parallel to each other and form the neck and neck canal. Neck hyphae are septate, may be branched, and remain unpigmented until late in development of the ascoma. A cavity within the ascoma is present only near the entrance to the ostiole until late in development. Centrum development is the Sordaria-type. The ascogonium branches in a horizontal layer among the bases of the paraphyses and produces short ascogenous hyphae which give rise to asci by crozier formation. Meiosis followed by a mitotic division gives rise to eight nuclei, each of which becomes enclosed within an ascospore. Mitosis and septum formation produce bicellular ascospores with two uninucleate cells. The apical apparatus of the ascus is inamyloid and annellascous but is often obscure. The haploid chromosome number is four.

Development and Cytology of Plectosphaerella cucumerina

Development of the ascoma of Plectosphaerella cucumerina begins with the formation of a coiled ascogonium that becomes surrounded by branches from the parent hypha or from neighboring hyphae or both. Paraphyses develop as rows of cells with the lower ones laterally expanded to form an apparent pseudoparenchyma. Apical meristcmatic cells of the ascoma grow upward parallel to each other and form the neck and neck canal. Neck hyphae are septate, may be branched, and remain unpigmented until late in development of the ascoma. A cavity within the ascoma is present only near the entrance to the ostiole until late in development. Centrum development is the Sordaria-type. The ascogonium branches in a horizontal layer among the bases of the paraphyses and produces short ascogenous hyphae which give rise to asci by crozier formation. Meiosis followed by a mitotic division gives rise to eight nuclei, each of which becomes enclosed within an ascospore. Mitosis and septum formation produce bicellular ascospores with two uninucleate cells. The apical apparatus of the ascus is inamyloid and annellascous but is often obscure. The haploid chromosome number is four.

A new root rot disease of tomato in Egypt caused by Fusarium tabacinum

Summary A destructive root rot of tomato ( Lycopersicon esculentum Miller ) caused by Fusarium tabacinum was discovered. The symptoms of the disease include rotting of the roots, yellowing of the foliage and wilting followed by death of the plant. Pathogenicity experiments revealed that cultivars UC 39, Pusa Ruby, Marglobe and Sious were susceptible. Seed and root exudates, in addition to volatile and gaseous exudates from germinating seeds and roots, stimulated conidial germination of the pathogen.

New Sunflower Disease Caused by Fusarium tabacinum

New Sunflower Disease Caused by Fusarium tabacinum

Potato growing in short rotations and the effect ofStreptomyces spp.,Colletotrichum coccodes, Fusarium tabacinum andVerticillium dahliae on plant growth and tuber yield

The yield of potatoes decreased as the frequency of growing this crop in a rotation increased, even in the absence of well-known soil pathogens e.g.Globodera spp. Soil disinfection with methylbromide or pasteurization at 60°C with steam for 30 min eliminated the rotation effect on yield, suggesting that it was caused by a complex of microbial pathogens. Organisms thought to belong to the complex wereC. coccodes, F. tabacinum, V. dahliae andStreptomyces isolates causing russet (netted) scab. Their effects on growth and yield were studied in non-sterilized soil that had never carried a potato crop before.V. dahliae decreases the yield of susceptible potato cultivars,C. coccodes may cause damage only late in the growing season in weakened plants. In the highly susceptible cv. Amethyst yield loss byV. dahliae was almost doubled in the presence ofC. coccodes. F. tabacinum did not influence growth and tuber yield neither singly nor in combination with other pathogens. TheStreptomyces isolates cause extensive root damage and yield loss in susceptible potato cultivars.

Fusarium tabacinum on tomato and other hosts in Australia

Fusarium tabacinum is recorded from several substrata in Australia, including tomato where its pathogenicity is demonstrated. The variable nature of the species in morphology and cultural characteristics is described and discussed.

Effect of ammonia and other soil volatiles on germination and growth of soil fungi

Ammonia found in the atmosphere above alkaline soil appeared to be responsible for the inhibition of germination in conidia of Botrytis cinerea and Penicillum nigricans. Other, as yet unknown, non-alkaline volatiles in the soil atmosphere are also involved in the inhibition of conidial germination of Trichoderma koningii, and T. hamatum and these and not ammonia are responsible for the inhibition of conidial germination in Verticillium nigrescens and germ tube growth in Fusarium culmorum, F. solani f. sp. phaseoli and Plectosphaerella cucumerina. Germ tube growth of Gliocladium roseum and Penicillium chrysogenum was unaffected by soil atmosphere or by ammonia at concentrations found in soil. Trichoderma harzianum was unaffected by ammonia and stimulated by a non-alkaline factor in the soil atmosphere. Soil fungi thus appeared to differ in their sensitivity to soil atmosphere and to ammonia released from soil.