Mycosphaerella coffeicola

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Mycosphaerella coffeicola
Arabica coffee infected with Cercospora berry blotch
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Fungi
Division: Ascomycota
Class: Dothideomycetes
Order: Capnodiales
Family: Mycosphaerellaceae
Genus: Mycosphaerella
Species:
M. coffeicola
Binomial name
Mycosphaerella coffeicola
Synonyms
  • Sphaerella coffeicola Cooke (1880)
  • Cercospora coffeicola
    M.A.Curtis
    (1881)
  • Ramularia goeldiana
    Sacc.
    (1892)
  • Cercospora coffeae
    Zimm.
    (1904)
  • Cercospora herrerana Farneti (1911)

Mycosphaerella coffeicola is a sexually reproducing fungal

plant pathogen
. It is most commonly referred to as the asexual organism Cercospora coffeicola.

Host and symptoms

There are 40 species in the genus Coffea (family Rubiaceae) that are susceptible to the disease caused by M. coffeicola, but only a few that are commercially relevant.[1] Arabica coffee (Coffea arabica L.) is the most significant of the susceptible species, affecting 70% of the world's coffee production.[2] Coffea arabica ranges in growth habit from a shrub to a small tree and has ovate, shiny, pointed leaves, with clustered white flowers.[1] The fruits begin as green berries which ripen to a deep red color. These are often called the coffee "cherries". Each fruit contains two seeds (i.e. coffee beans) in a drupe.[2]

Symptoms of M. coffeicola vary depending on the plant organ affected. These differing symptoms help explain the various common names for the disease: Cercospora "Leaf Spot" and Cercospora "Berry Blotch" (Cercospora is reference to the deuteromycete stage).

Colletotrichum gloeosporioides), though symptoms from these organisms should not be falsely attributed to M. coffeicola.[1]

Environment

Disease is often affected by the environment and the changing conditions. M. coffeicola is a tropically adapted pathogen due to its host narrow geographical range around the equator. Favorable environmental conditions around the equator are warm and humid wet seasons followed by a warm and dry season. The highest disease pressure occurs when the temperature is 20–28 °C (68–82 °F) and continuous environmental wetness for 36–72 hours.

conidia to disperse. A nitrogen-deficient plant as well as a plant with excess nitrogen favors disease prevalence, making well-timed fertilizer applications important.[4] Other factors that can increase disease incidence are insufficient shade, herbicide injury, plant stress, and other diseases caused by nematodes.[1]
The reason for increased disease is that stressed plants are more susceptible.

Disease cycle

Conidia of Mycosphaerella coffeicola are produced year-round and enter the coffee plant through

Conidiophores and conidia are formed here, and then dispersed by wind or by water.[4] Conidiophores emerge in bundles of 3–30 and are often septate and branched. Conidia are elongated, multiseptate, and either straight or slightly curved. They appear glassy and have a conspicuous hilum.[5] The spores can splash from one leaf to another, or onto flowers and berries causing secondary infections.[6] The continuous production of conidia guarantees infection at multiple stages of plant development (in leaves, flowers, and fruit).[4] The fungus can overwinter (i.e. survive a dry season) as conidia in dropped, infected leaves for up to two months. Once humid conditions return, conidia infect new plants or plant parts.[6]

Management

Prevention is the most effective method of managing M. coffeicola. Risk factors for this pathogen include: prolonged (24–72 hours) humid environment, poor soil nutrition, and plant stress caused by increased planting density, herbicide injury, weeds, drought, and over irrigation. To manage humidity a farmer can prune to allow for air circulation and ensure the soil has proper drainage.[1] In order to maintain proper plant nutrition, soil testing and a fertilization regiment are essential for combating this pathogen. Plant symptoms such as chlorosis, leaf curling, and bronzing along the edges of leaves can be used to diagnose specific nutrient deficiencies. For example, if a plant has leaves bronzed along edges, cupped down-ward; new leaves dead; eventual die back of shoot tips, then it is likely the plant has a calcium deficiency.[7] To reduce plant stress, a farmer can use herbicides to combat weeds but must be careful not to damage the plant in process. Also to minimize competition between adjacent crops, it is important to properly space coffee plants in 8 ft. by 8 ft. areas. Stress can further be minimized if post and pre-harvest damage by machinery or laborers is avoided. To avoid wilting stress plants should be properly irrigated .[8] However, if a crop already has M. coffeicola, copper fungicide is effective. In Hawaii, farmers often spray tri-annually, using 1.5–6 lbs of fungicide per 50–100 gallons water, containing 30–80% copper hydroxide.[1] "Sprays should coincide with dry weather and calm winds. Three spray applications per season should suffice (occurring approximately once per month), beginning at flowering. Thorough coverage of the plant canopy is very important. Large farms in Hawai‘i utilize tractor-mounted mist blowers."[1]

Importance

Coffee is the 15th most valuable traded commodity in the world.[9] There are approximately 25 million farmers and coffee workers in over 50 countries involved in producing coffee around the world.[10] M. coffeicola is present throughout the world and can account for yield losses as high as 15% annually.[11] In parts of Puerto Rico nearly 50% of cultivated coffee acres are affected by this disease, resulting in yield losses around 15%.[11] Due to the fact Mycosphaerella coffeicola proliferates in a sustained warm, humid environment, M. coffeicola is most prevalent in the low-elevation Central American farms where high daily average temperatures and high humidity are observed.[12] Literature suggests that M. coffeicola is not a significant problem in Ethiopia and Uganda, Africa's top coffee-producing countries. Conversely, M. coffeicola is common in Hawaii but not economically important due to proper management practices and the environment does not have the prolonged humid environment necessary for proliferation.[8]

Pathogenesis

The genus Cercospora shows a wide variety of infection processes; even a single species can show different patterns on different hosts.

photoactivated perylenequinone called cercosporin. In the dark, cercosporin lacks toxicity but when exposed to light, it is converted into a toxic form of activated oxygen. This damages membrane lipids resulting in cell death and nutrient leakage. The pathogen uses the leaked nutrients as an energy source.[14] M. coffeicola is a wind-borne pathogen that utilizes cercosporin [15] to infect both the berries and leaves of the coffee plant. Lesions on infected berries produce conidia 17 days after inoculation. If on the leaves, conidia are produced 38 days after inoculation.[8]

After the spores land on the plant surface, one to several germ tubes are produced. The germ tubes aggregate and penetrate the plant via the stomata or cracks in the leaf surface.[13] The fungus can survive 36 days as conidia and 218 days as mycelium, which suggests that M. coffeicola overwinters in lesions.[15] On berries, the lesions are tan and sunken and can occur while the berry is green. As the lesion matures, it becomes deeply depressed with an ashy center and may penetrate down to the coffee bean to affect the bean quality and taste. If on mature fruits, the lesion measures 1–4 mm in diameter.[12][15]

There is conflicting information if fungal strains on berries can infect leaves and vice versa.[16]

See also

References

  1. ^ a b c d e f g h i j Nelson, Scot (June 2008). "Cercospora Leaf Spot and Berry Blotch of Coffee" (PDF). Plant Disease, College of Tropical Agriculture and Human Resources, University of Hawai'i at Manoa. Retrieved 2015-10-19.
  2. ^ a b "Specialty Coffee Association of America". scaa.org. Retrieved 2015-10-22.
  3. ^ a b Smith, Virginia Easton and Nelson, Scot C. (March 2004). "Coffee Pests and Diseases: Diseases caused by Cercospora" (PDF). Hawaii Coffee Quarterly. Retrieved 2015-10-22.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ a b c d e Gaitán, Alvaro Leo (2015). Compendium of Coffee Disease and Pests. St. Paul, MN: American Phytopathological Society. pp. 27–28.
  5. ISBN 978-1-84593-129-2.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  6. ^ a b Rutherford, Mike A. (2006). "Pest and Disease of Coffee in Eastern Africa: A Technical and Advisory Manual" (PDF). www.agriskmanagementforum.org. Crop Protection Program of the UK Department for International Development. Retrieved 2015-10-19.
  7. ISBN 978-974-7946-78-9
    .
  8. ^ a b c Bittenbender, H.C. (2008). "Growing Coffee In Hawai'i". College of Tropical Agriculture and Human Resources.
  9. ^ "Starbucks exec uses debunked coffee statistic at hearing".
  10. ^ Turner, Walker (October 2011). "Global Exchange". Global Exchange.
  11. ^ a b Inglés, Miguel Monroig (October 2002). "IPM Centers" (PDF). ipmcenters.org. USDA.
  12. ^ a b Trujillo, Eduardo (January 1995). "Serious Economic Pests of Coffee that May Accidentally be Introduced to Hawai'i" (PDF). College of Tropical Agriculture and Human Resources.
  13. ^
    ISSN 1439-0434
    .
  14. ^ "Cercosporin: A Photoactivated Toxin in Plant Disease". www.apsnet.org. Archived from the original on 2015-12-08. Retrieved 2015-12-03.
  15. ^
    doi:10.1016/S0007-1536(70)80156-5
    .
  16. JSTOR 42556029
    .
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