Marssonina leaf fall disease
| Marssonina leaf fall disease | ||||||||||||
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Infested leaf |
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| Diplocarpon mali | ||||||||||||
| Y. Harada & Sawamura |
The Marssonina-leaf drop disease is through an infection with the fungus Diplocarpon mali caused disease of apple trees . Most of the leaves on severely infested trees can be lost. While the disease previously only occurred in Asia and America , it has also been increasingly occurring in Europe since the beginning of the 21st century .
Because of the black spots that appear on the leaves after infection, the condition is also known as Marssonina leaf spot disease . The disease is known internationally as Marssonina blotch or Marssonina leafspot .
Pathogen
Macroscopic features
On the leaves of various types of apples, small, 5 to 10 mm large, grayish-brown spots, with some purple spots on the edge, are visible, which are produced by the secondary fruit form . The spots can be elongated or flow into one another, which gives them an irregular shape.
Microscopic features
Only conidia of the minor fruit form Marssonina coronaria are produced on the leaves that remain on the tree . According to literature, fruiting bodies of the main fruit form Diplocarpon mali are formed on the leaves that overwinter on the ground. These fruit bodies are cup-shaped apothecia that are 120 to 220 µm wide and 100 to 150 µm high. The tubes are broad, club-shaped to elongated, 55–78 µm wide and 14–18 µm long, and always contain eight ascospores . These are usually simply septate , elongated to elliptical, straight or curved, hyaline and measure 23–33 µm in length and 5–6 µm in width. Thread-like paraphyses are formed between the tubes , which are septate one to two times, are usually slightly widened at the tip and reach the same height as the tubes. However, ascospores or the associated fruiting bodies have not yet been detected in Europe. The conidia of the minor fruit form are formed in concentric acervuli . They are jet black, lens-shaped and 100 to 200 µm in diameter. Club-shaped conidia carriers are formed on which the spores are then pinched off. These are ampoule-shaped, hyaline and 4–6 × 1–2 µm in size.
Taxonomy
The basionym of Diplocarpon mali goes back to the German botanist and mycologist Paul Christoph Hennings , who first described the fungus in 1905 under the name Marssonia mali .
The leaf spot disease caused by the fungus was first described in 1903 by Job Bicknell Ellis and JJ Davis under the name Ascochyta coronariae ELLIS & DAVIS. In 1912 he was assigned to the Melanconiales order by PA Saccardo & J. Dearness, which is why he was named Marssonia coronariae SACC from this point on . & DEARN. was designated. The mycologists ignored the fact that the genus Marssonia had already been renamed Marssonina by Magnus in 1906 . The correct naming as Marssonina coronariae then took place in 1914 by Davis. The terms A. coronariae and M. coronaria were also incorrect, as the grammatically correct form would have been A. coronaria and M. coronaria .
In 1974 Marssonina coronariae was finally assigned as an anamorph of the main form Diplocarpon mali .
As a representative of the genus Diplocarpon , the causative agent of Marssonina leaf spot disease is related to Diplocarpon rosae , the causative agent of rose black soot . The fungus, however, is not closely related to Ophiognomonia leptostyla , the causative agent of Marssonina leaf spot disease in walnuts.
Epidemiology
The fungus attacks plants from the genus Malus . The main host plant is the cultivated apple ( Malus x domestica ), but ornamental and wild forms such as the cherry apple ( Malus baccata ) can also be attacked. An infestation of ornamental quinces ( Chaenomeles ) has also been described.
In the cultivated apple, some apple varieties appear to be particularly susceptible to infection with Diplocarpon mali ; these include the varieties ' Topaz ', ' Gala ', ' Jonagold ', ' Golden Delicious ' and 'Luna', which are common in commercial fruit growing in Europe . In Asia, the “ Fuji ” variety was found to be highly sensitive .
The main distribution area of the mushroom is in Asia (China, India, Japan, Korea and Taiwan). In 1907 the fungus was described as a new pathogen causing a plant disease in Japan, where it then led to major losses in apple cultivation in the 1910s. The infection was largely suppressed by using copper-containing Bordeaux broth as a fungicide . In Korea the infection is the most economically important plant disease in the commercial cultivation of apples. The fungus is also found in the USA (Wisconsin), Canada and South America (Brazil, Panama).
With the exception of historical evidence in Romania , Europe was considered free of the infection until the turn of the millennium. Diplocarpon mali was detected for the first time here in 2001 and 2002 in Forno Canavese in the Italian province of Turin . In 2010 the disease appeared for the first time in Germany in an organically farmed fruit farm in Baden-Württemberg. In 2011 the pathogen was detected in various parts of Baden-Württemberg and in 2012 in Hesse as well. The actual current distribution in Germany is so far unclear. It is assumed that the fungus has now settled across Baden-Württemberg. It is also unclear whether the infection had not been established in Germany for some time and whether the symptoms only became particularly noticeable due to the wet summers from 2010 to 2012 in the following three years. Comparable symptoms had been observed in individual cases in Baden-Württemberg before 2010 without the pathogen being detected. So far, infections have mainly affected organically farmed apple orchards and plants with scab-resistant varieties, which is attributed to the fact that significantly fewer fungicides are used against apple scab ( Venturia inaequalis ), which also combat diplocarpon mali . Outbreaks have also been observed in home gardens and on orchards where fungicides are not used.
In Austria , an infection with Diplocarpon mali was first detected in August 2011 in the places Mellach , Rothgmos , Kopfing in Styria and in Puch in Lower Austria. Here the fungus had attacked trees of various apple varieties in organically managed intensive orchards as well as in orchards . The disease also appeared for the first time in Switzerland in 2011 . Organic farms in the Lake Constance region were affected here.
The fungus spreads naturally via conidia and probably also via ascospores with the wind and water. So far it is not known over what distances the spores can spread through the wind, but it is assumed that the distances are rather small. A spread via insects over longer distances is possible. In the case of new plantings, the pathogen can be spread via the seedlings if there are still leaves or remains of leaves on the young plants. It is also possible to introduce them into previously unused systems via spores or infected leaves adhering to tools or machines. A spread via infected fruits is considered to be potentially possible, but practically unlikely, since fruits are intended for use, but are usually not brought into other orchards.
The exact route of spread of the infection to and in Europe has not yet been identified.
Infection cycle
The infection cycle is currently not fully researched. According to the literature, ascospores are released from the main fruit form ( apothecia ) that form in winter , from which the primary infection originates in spring. The occurrence of ascospores has not yet been proven in Europe. In summer, the fruiting bodies of the asexual reproductive form (acervuli) with conidia (secondary fruit form Marssonina coronaria) are formed. The conidia are two-celled, constricted and have an average size of 20 × 8 µm.
The conidia, from which the secondary infection originates, are spread by wind and rain. A prolonged period of bad weather can lead to an epidemic spread of the infection. In autumn, the fruiting bodies of the main fruit form Diplocarpon mali form again and overwinter in the fall foliage.
For its optimal development, the fungus needs a longer period of humid weather and moderate temperatures of around 20-25 ° C, during which the leaf surface is moistened for a longer period of time. However, the overwintered fungus can germinate at temperatures as low as 5 ° C.
Symptoms
Symptoms of the infection develop in summer after long rainy seasons. First, gray-black, diffuse leaf spots are visible on the upper side of the leaf. These spread increasingly and run into one another over time. The infected cells die, which leads to a necrotic mottling of the leaves, which can be seen more clearly on the upper side than on the lower side.
Eventually small round to oval black fruiting bodies, called acervuli, break through on the leaf surface. Especially in prolonged warm and humid weather, half of the leaves can be infected within a short time, turn yellow and finally fall off prematurely, while the fruits are not yet fully ripe on the tree. If the infection pressure is high, leaf fall can begin as early as two weeks after infection, which was the case with some outbreaks in mid-August. Due to the reduced leaf mass, the fruits are no longer adequately supplied with nutrients, which disrupts their development. The storage of starch is reduced and the fruits have a lower fruit weight and are poorly colored, which leads to a reduced fruit quality. The disease also leads to yield losses in the following year, as the infected trees do not bloom well and budding is disturbed in the coming spring.
It has been described from India that the infection can cause round spots on the fruits. These symptoms have not yet been described in Europe.
The symptoms caused by Diplocarpon mali are similar to those caused by fungi of the genus Phyllosticta . For a reliable diagnosis, the pathogen can be cultivated on peptone-dextrose-potato agar. It can also be detected with the help of a PCR.
Combat
In commercial fruit growing, the fungus is captured by the usual fungicide treatments against apple scab and apple powdery mildew. Diplocarpon mali , however, shows a relatively low sensitivity to the copper preparations used in organic farming to combat fungal infections. In Japan, diplocarpon mali strains were also found in the late 1990s that showed resistance to the active ingredient thiophanate-methyl .
Since the different apple varieties are differently sensitive to the infection, an effective preventive measure against the disease could consist in the selection of resistant varieties when starting a new orchard. Work is currently being carried out, particularly in Korea, on identifying or breeding apple varieties that are resistant to the diplocarpon infection.
Hygiene measures, in particular the disinfection of tools and the removal of infected leaves in autumn, can limit the recurrence of the disease in the following year and the spread of the infection. Careful pruning of the fruit tree ensures that all parts of the tree are well ventilated, which means that the leaves can dry out more quickly.
The Plant Protection Organization for Europe and the Mediterranean (EPPO) has included the infection in its warning list (EPPO Alert list). She assumes that the infection will continue to spread in Europe and that the fungus could at least establish itself in various other regions in Germany. Since it must be assumed that the infection has already settled in several locations, the natural spread can probably only inadequately be contained in the future.
Individual evidence
- ↑ a b c d e Yukio Harada, Kenzo Sawamura, Koki Konno: Diplocarpon mali, sp. nov., the Perfect State of Apple Blotch Fungus Marssonina coronaria . In: Japanese Journal of Phytopathology . tape 40 , no. 5 , 1974, p. 412-418 , doi : 10.3186 / jjphytopath.40.412 ( PDF ).
- ↑ P. Hennings. Engl. Bot. Jahrb. XXXVII, 1905, p. 164
- ^ PA Saccardo: Ann. mycol. 10 (3): 313 (1912)
- ↑ P. Magnus: Necessary change of the name of the mushroom genus Marssonia. In: fish. Hedwigia 45, 1906, pp. 88-91.
- ↑ a b c d e f g h i j k l Diplocarpon mali (anamorphic: Marssonina coronaria) - Marssonina blotch of apple. ( Memento of the original from April 1, 2016 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. on the homepage of the European and Mediterraneaen Plant Protection Organization (EPPO), status: March 2015, accessed on April 1, 2016
- ↑ a b c d e Gritta Schrader, Silke Steinmöller: Express - PRA to Diplocarpon mali Y. HARADA & SAWAMURA. ( Memento of the original from April 1, 2016 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. Julius Kühn Institute, Institute for National and International Plant Health Affairs. January 9, 2013, accessed April 1, 2016
- ↑ a b c d e Center for Agriculture and Bioscience International (CABI): Diplocarpon mali. In: Invasive Species Compendium (ISC), Wallingford, UK, as of March 2016, accessed April 1, 2016
- ^ A b c Jan Hinrichs-Berger, Gabriele Müller: On the occurrence of Marssonina coronaria on apples in Baden-Württemberg. In: Journal for Cultivated Plants. 65 (9), 2013, pp. 347-350, doi: 10.5073 / JfK.2013.09.02 .
- ↑ G. Tamietti, A. Matta: First Report of Leaf Blotch Caused by Marssonina coronaria on Apple in Italy. In: Plant disease. 87 (8) August 2003, p. 1005, doi: 10.1094 / PDIS.2003.87.8.1005B .
- ↑ Ulrike Persen, Robert Steffek, Claudia Freiding, Gerhard Bedlan: First record of Diplocarpon mali on Malus domestica in Austria. In: Journal for Cultivated Plants. 64 (5). 2012, pp. 168-170 ISSN 1867-0911
