Didymella bryoniae
| Didymella bryoniae | ||||||||||||
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Didymella bryoniae , symptoms of infestation on watermelon |
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| Didymella bryoniae | ||||||||||||
| ( Auersw. ) Rehm |
Didymella bryoniae is a microscopic hose fungus (Ascomycota) from the Didymellaceae family. The phytopathogenic fungus causes the so-called rubber stem disease in various crops. Sometimes the disease is also known as stem blight . The species, which is widespread worldwide today, primarily attacks the cucurbitaceae such as pumpkins, cucumbers and melons and thus causes significant economic damage.
description
Didymella bryoniae has a pleomorphic development cycle , that is, the species has a main fruit form in which the ascospores are formed for sexual reproduction, and a minor fruit form in which asexual conidiospores are formed.
Description of the main fruit form
In Didymella bryoniae , as with many sac fungi, in the course of sexual reproduction, a fruiting body is formed from very closely interwoven cell threads, the ascocarp . More precisely, the ascocarp is a pseudothecium ; this is a fruiting body, on the top of which there is a small pore, the ostiole .
Pseudothecia
The pseudothecium is spherical, dark to black, sunk into the tissue of the host plant and then erupts. It is often found on shoot axes , leaves or fruits of the host plant and has a diameter of 140 to 200 micrometers. The surface has a conical elevation up to 30 micrometers high, on which the 30 to 55 micrometer diameter ostiole is located.
The wall of the pseudothecia is thickened on the sides and at the base. The wall is 18 to 21 micrometers thick at the top. The side wall is between 20 and 30 micrometers thick and the base is between 25 and 40 micrometers thick. The wall consists of two layers: an outer layer of 4 to 6 layers of brown to dark brown angular cells and an inner layer of 2 to 5 (at the base also more) layers of hyaline or almost hyaline angular cells. The cells of the wall are about 10 micrometers in diameter; however, the cells of the top wall and the inner layer at the base are smaller.
Asci
In the pseudothecium there are several tubes (asci) in which the ascospores arise. In Didymella bryoniae , the asci are cylindrical or approximately club-shaped. They are sessile or short-stalked and straight or curved. They measure between 60 and 90 micrometers in length and are 10 to 15 micrometers wide.
The double-walled (so-called bitunicate) Asci consist of a thin, brittle outer shell and a thick, elastic inner wall. As soon as the spores are ripe, the outer shell tears open so that the inner wall can absorb water. As a result, it begins to swell, together with the spores it contains, until they protrude from the ascocarp through the ostiole and the spores can be released into the free air flow one after the other.
Pseudoparaphyses
In addition to the asci, the pseudothecia also contain so-called pseudoparaphyses , which together with the asci form the hymenium (the fruit layer) of the fungus. The pseudoparaphyses are sterile hyphae ends that stand between the asci. In Didymella bryoniae they are hyaline and form a septum (a strong thickening of the cell wall) at the end . They are spaced 3 to 10 micrometers apart and are 2.5 to 4 micrometers thick. In contrast to other species, the pseudoparaphyses in Didymella bryoniae are persistent, i.e. they remain throughout the fruit's ripeness.
Ascospores
Each ascus contains 8 ascospores, these are biseriat, that is, arranged in two rows. They are oval or almost inversely ovoid, straight or curved. They are hyaline with a septum in the middle or just above, and measure 14 to 18 × 2 to 6 microns. The ascospores are slightly constricted on the septum. They consist of two cells: a slightly larger upper one and a smaller lower one. The wall is smooth. There are small droplets of oil inside the cells.
Description of the minor crop shape
The secondary crop form Phoma curcurbitacearum is found much more frequently than the sexual form in the infected tissue of the host plant . The asexual fruiting bodies are - in contrast to the sexual pseudothecia - called pycnidia .
Pycnidia
The pycnidia are found on the stems, leaves and fruits of the host plant. They stand solitary or like a herd. The pycnidia are spherical or irregularly spherical and sunk deep into the host tissue, but break out of it. They are dark brown, their diameter is between 80 and 380 micrometers. The wall consists of 2 to 4 layers of yellowish-brown cells. The cell wall of the outermost layer is thickened. The surface is smooth with growing hyphae . Each pycnidia has one ostiole (very rarely two), which expand to form a kind of neck as the fruit ripens.
Inside the pycnidia there is a lawn of conidiogenic cells , i.e. cells on which the conidia arise in an asexual way . The conidiogenic cells are white or pale yellow-brown.
Conidia
The conidia in Didymella bryoniae are very variable. They are cylindrical with rounded ends, spherical, almost spherical or oval, and straight or curved. Smaller conidia are usually without a septum, larger ones with a septum. Conidia with two septa are also extremely rare.
The hyaline conidia measure between 6 and 13 micrometers × 2 to 4.5 micrometers.
distribution
Didymella bryoniae is cosmopolitan . The main focus of the distribution is outside the tropics . In the subtropics the species is widespread, in the temperate zones it occurs mainly in greenhouses .
Experiments with watermelons ( Citrullus lanatus ) have shown that the species attacks plants at temperatures between 7 and 29.5 ° C. The optimum is at 24 ° C, at 29.5 ° C the species can only survive to a very limited extent. Complete development, including teleomorphs, only takes place between 20 and 28 ° C.
In the laboratory, the fungus can be cultivated well on wheat flour agar and malt agar as a nutrient medium .
Spread
The species was first detected in Germany in 1869 on a bryony ( Bryonia sp. ). The first record of Didymella bryoniae on a cultivated plant comes from Italy, where it was found on a sugar melon ( Cucumis melo ) in an unknown year and described by Giovanni Passerini as Didymella melonis in 1885 . In 1891 the species was identified independently on watermelons ( Citrullus lanatus ) in France and in Delaware in the United States . At the beginning of the 20th century, the species was then detected in the American Midwest and Puerto Rico. In the 1950s the species was reported in Pakistan, from the 1960s there are records from Malawi and Tanzania, and it reached New Zealand by the 1980s at the latest. How the species was able to spread so quickly has not yet been conclusively clarified; however, the spread of infected host seeds by humans probably contributed to this.
Life cycle and ecology
If conidia or ascospores of Didymella bryoniae meet a suitable host plant, they settle there and begin to germinate there, depending on temperature, humidity, pH value and other conditions. The conidia initially swells and a germinal thread grows out. Germination preferably begins when the host plant is damaged; Didymella bryoniae can only germinate on a completely undamaged plant under otherwise optimal conditions.
Cell division creates a hypha , a cell thread made up of several elongated cells linked together. This branches out several times as it grows and thus forms an extensive hyphae ( mycelium ). If the growth has progressed sufficiently and there are enough nutrients available, fructification begins and pycnidia arise in which new asexual conidia mature and are released.
The sexual part of the life cycle is initiated as soon as two matching hyphae meet. These come from the same hyphae that also forms the asexual spores. It comes at Didymella bryoniae often for self-fertilization, a property that as homothallic is called. After mating, a pseudothecium forms and releases new ascospores.
If the host plant dies or infected parts fall down, the pseudothecia can remain in the soil for up to two years and then still be blown away and release ascospores.
Host plants
| Affected genus | Number of species affected |
|---|---|
| Bennincasa | 1 |
| Bryonia | 3 |
| Citrullus | 2 |
| Cucumis | 3 |
| Cucurbita | 5 |
| Cyclanthera | 1 |
| Lagenaria | 1 |
| loofah | 2 |
| Momordica | 2 |
| Sechium | 1 |
| Sicyos | 1 |
| Trichosanthes | 1 |
The fungus attacks the cucurbit family (Cucurbitaceae) and has been identified in at least 12 genera and 23 species from this family.
It attacks pumpkins ( Cucurbita ) particularly often , especially the musk pumpkin ( Cucurbita moschata ) and the garden pumpkin ( Cucurbita pepo ). Cucumbers ( cucumis ), in particular cucumbers ( Cucumis sativus ), and species of the genus Citrullus , in particular the watermelon ( Citrullus lanatus ), are attacked just as frequently as pumpkins .
Didymella bryoniae was isolated from the nightshade family (Solanaceae), melon tree family (Caricaceae) and primrose family (Primulaceae) much less frequently . Since 1977, however, the species has appeared regularly on tomatoes ( Solanum lycopersicum ) in Dutch greenhouses, where it causes great damage.
Antagonists
The tubular fungus Trichoderma longibrachiatum can parasitize the hyphae of Didymella bryoniae and weaken the fungus massively.
The bacteria Pseudomonas chlororaphis or Lysobacter gummosus , Paenibacillus polymyxa and Serratia plymuthica are also antagonists of the species and can inhibit growth.
Clinical picture
Didymella bryoniae causes so-called gum stem disease in its host plants.
First, spots form on the leaves that spread from the leaf edge towards the center. The lesions grow very quickly and can spread by half a centimeter in 12 hours. This forms necroses that become lighter towards the edge of the leaf and gradually dry up. Between healthy and diseased tissue, the leaf is dull and darker green. Pycnidia and pseudothecia form on the necrotic, brown to light beige spots, which appear as small black dots and are sometimes arranged in a ring. The dots can be easily recognized without a magnifying glass.
The shoot axis is also affected, where similar symptoms appear. Viewed from a distance, the places appear gray due to the many pycnidia. They are mostly found in the lower part of the plant and especially up to the root neck . In the upper part of the plant, they tend to appear at branch points on side shoots. At a later stage, the infestation can encompass the entire stem and cause the plant to wither or die. This leads to a rubbery consistency of the stem, which is what gave the disease its name. Yellowish, transparent, rubbery sap exudates (exudate) may appear on the stem, which dry up and remain as solid drops.
Fruits can also be attacked, whereby the fungus usually occurs at the stigma of the flower attachment point, the point where the remains of the flower remain on the fruit. When the fruit is at an advanced stage, the tip looks contracted. When cutting open from the tip, the fruit core is discolored from light to dark brown. Later the tip will shrink completely. There, too, a lot of pycnidia form, which makes the fruit tip look black. Even after the harvest, the fungus can continue to develop and destroy fruits. With melons and pumpkins, brown, watery, sunken round spots appear, depending on the variety and species. In an advanced stage, fruit bodies, the pycnidia or pseudothecia, can also form in these. If the fruits are stored for a long time in moist conditions, whitish mycelial lawns can also form on the sunken areas (lesions) . The fungus forms partially concentrically sunken discolored round spots. In the case of fruits, an infection is also known as Didymella rot , and the fruits are considered unhealthy and spoiled even when the symptoms begin.
Economical meaning
The economic damage caused by Didymella bryoniae is immense. In the state of New York in the United States, around 50% of winter squash production is affected, causing crop losses of up to 75% in the crops concerned (2001 figures), although New York is not in the subtropics. In the Lower Rio Grande Valley in Texas in 1997 68.4% of the production of goods in cantaloupes from Didymella bryoniae affected, which caused an economic loss of about 15 million US dollars only in this small, limited area. For Fiji , which has a tropical climate, crop failures of 30% were estimated for watermelons ( Citrullus lanatus ) in 2000.
In agriculture, Didymella bryoniae is controlled chemically with fungicides . The active ingredients trifloxystrobin - a strobilurin - and iprodione are used in particular. A substantial market has developed from this. Bayer CropScience alone estimates annual sales of 300 million euros with trifloxystrobin preparations.
Systematics
Didymella bryoniae belongs to the genus Didymella . The genre has not yet been treated as a monograph and is very confusing. MycoBank lists over 400 species in the genus, but many of them are controversial.
The position of the genus Didymella within the taxonomic system is moving. Originally the genera Didymella and Mycosphaerella formed the family of Mycosphaerellaceae . Thereafter, the genus was initially counted among the Pleosporaceae , then the Phaeosphaeriaceae or the Venturiaceae . In 2007, researchers identified the genus incertae sedis . It was not until 2009 that molecular genetic studies revealed that a new family, the Didymellaceae , best describes the taxonomic position of the genus. However, it is undisputed that the species lies within the order of the Pleosporales .
In 1981, Corlett presented a work that classifies various Didymella according to morphological criteria. As a result, Didymella castillejae - a species that primarily affects Castilleja - looks most similar to Didymella bryoniae .
A work from 2009 that evaluates a DNA sequence analysis of the ribosomal RNA in two regions ( LSU = 60S and SSU = 40S) comes to the following relationships:
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Since Didymella bryoniae is closer to these species than to other species in the genus Didymella , it seems clear that Didymella is paraphyletic . An older study from 1999 found a close relationship to Leptosphaerulina chartarum and Leptosphaerulina crassiasca . This close relationship is confirmed in the 2009 study.
Mycological history
The anamorphic of the species was first described as Sphaeria cucurbitacearum long before the teleomorph in 1823 by Elias Magnus Fries in his Systema mycologicum . Pier Andrea Saccardo then correctly placed the species in the Phoma form taxon in 1884 .
The first description of teleomorphs goes back to Bernhard Auerswald in 1869. In his work Mycologia europaea. Illustrations of all the sponges in Europe , on which he wrote together with Ludwig Rabenhorst and which is illustrated with very elaborate lithographs by Wilhelm Gonnermann , he described the species as Sphaerella bryoniae . He chose the species epipheton bryoniae after the host plant of a bryony ( Bryonia sp. ) From which he had isolated the type .
Only one year later, Leopold Fuckel described the same species as Sphaeria bryoniae in the yearbooks of the Nassau Association for Natural History . In 1880 Heinrich Rehm correctly recognized that the species of the genus Didymella should be added .
swell
Unless otherwise stated, the information in this article is taken from the sources indicated under literature:
literature
- Paul Holliday: Fungus Diseases of Tropical Crops . Dover Publications, 1995, ISBN 0-486-68647-7 , pp. 132–133 (English, limited preview in Google Book Search).
- Albert O. Paulus, Peter Gladders, Steven T. Koike: Vegetable Diseases: A Color Handbook . Academic Press, 2009, ISBN 978-0-12-373675-8 , pp. 232–233 (English, limited preview in Google Book Search).
- M. Corlett, WR Jarvis, IA Maclatchy: Didymella bryoniae . In: Fungi Canadenses . tape 303 , 1986, ISSN 0823-0552 (English).
- Gerhard H. Boerema, J. de Gruyter, ME Noordeloos: Phoma Identification Manual: Differentiation of Specific and Infra-specific Taxa in Culture . 2004, ISBN 0-85199-743-0 , pp. 236-239 (English).
Individual evidence
- ↑ a b c d e Anthony P. Keinath: From Native Plants in Central Europe to Cultivated Crops Worldwide: The Emergence of Didymella bryoniae as a Cucurbit Pathogen . In: Cucurbitaceae 2010 . 2010, p. 7–9 (English, cuke.hort.ncsu.edu [PDF] November 14-18 ).
- ↑ Holliday, p. 132.
- ↑ Boerema et al., P. 237.
- ↑ Herbert Huss: The mushroom Didymella bryoniae conquers the pumpkin fields . In: Vegetable growing practice . tape 18 , no. 3 , p. 8–9 ( raumberg-gumpenstein.at ).
- ↑ Internet source | author = DF Farr, AY Rossman | date = 2010 | titel = Didymelly bryoniae | werk = Fungal Databases, Systematic Mycology and Microbiology Laboratory | hrsg = ARS, USDA http://nt.ars-grin.gov/fungaldatabases/ (Link not available)
- ↑ Gil Rodrigues dos Santos, MarisaÁlvares da Silva Velloso Ferreira, Marco Aurélio Caldas de Pinho Pessoa-Filho, Márcio Elias Ferreira, Adalberto Corréa Café-Filho: Host Specificity and Genetic Diversity of Didymella bryoniae from Cucurbitaceae in Brazil . In: Journal of Phytopathology . tape 157 , no. 5 , 2009, p. 265-273 , doi : 10.1111 / j.1439-0434.2008.01475.x (English).
- ↑ Boerema et al. , P. 238
- ↑ Boerema et al. , P. 239
- Jump up ↑ A. Veronesi, R. Roberti, A. Finestrelli, A. Cesari, A. Pisi: Control of Didymella bryoniae (Auersw.) Rehm by Trichoderma longibrachiatum . In: Journal of Plant Pathology . tape 86 , no. 4 , 2004, p. 336 (English).
- ↑ M. Fürnkranz, B. Lukesch, H. Müller, H. Huss, M. Grube, G. Berg: Microbial diversity inside pumpkins: microhabitat-specific communities display a high antagonistic potential against phytopathogens . In: Microbial Ecology . tape 63 , no. 2 , 2012, p. 418-428 , PMID 21947430 (English).
- ^ Arden F. Sherf, Alan A. MacNab: Vegetable Diseases and Their Control . 2nd Edition. Wiley-Interscience, New York 1986, ISBN 0-471-05860-2 , pp. 340-346 (English).
- ↑ Gerd Crüger: Plant protection in vegetable growing . 3. Edition. Ulmer, Stuttgart 1991, ISBN 3-8001-5135-9 , pp. 200-201 .
- ^ MR Howard: Hydroponic Food Production . 6th edition. Lawrence Erlbaum Associates, 2001, ISBN 0-931231-99-X , p. 488 (English).
- ↑ Paulus et al. , P. 230
- ↑ BLE - Marketing standards and application aids - How can Didymella rot in cucumbers be recognized and assessed? In: ble.de. October 1, 2013, accessed March 4, 2019 .
- ↑ Lee Stivers: Crop Profile: Squash in New York. March 2, 2001, accessed May 14, 2012 .
- ↑ M. Miller, T. Isakeit, Benny Bruton, Jiuxu Zhang: Fungicidal Sensitivity of Didymella Bryoniae Isolates from South Texas . In: Proceedings of the International Plant Protection Congress . April 29, 1998 (English, abstract ). abstract ( Memento of the original from May 17, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Apaitia R. Macanawai: Gummy stem blight of Watermelon . In: Technical Bulletin of the Ministry of Primary Industries . No. September 2 , 2011 (English).
- ↑ Bayer acquires new fungicide from Novartis. (PDF) Bayer CropScience, October 17, 2000, accessed May 21, 2012 .
- ↑ Didymella. In: MycoBank. Retrieved May 14, 2012 .
- ↑ Johannes de Gruyter, Maikel M. Aveskamp, Joyce HC Woudenberg, Gerard JM Verkley, Johannes Z. Groenewald, Pedro W. Crous: Molecular phylogeny of Phoma and allied anamorph Genera: Towards a reclassification of the Phoma complex . In: Mycological Research . tape 113 , 2009, pp. 508-519 , doi : 10.1016 / j.mycres.2009.01.002 (English).
- ↑ Michael Corlett: A taxonomic survey of some species of Didymella and Didymella-like species . In: Canadian Journal of Botany . tape 59 , no. 11 , 1981, pp. 2016–2042 , doi : 10.1139 / b81-264 (English).
- ↑ Denise MW Silva-Hanlin, Richard T. Hanlin: Small subunit ribosomal RNA gene phylogeny of several Loculoascomycetes and its taxonomic implications . In: Mycological Research . tape 103 , 1999, pp. 153-160 (English, abstract ).
- ^ Index Fungorum. Retrieved May 14, 2012 .
