Phytophthora colocasiae
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Sporangia of Phytophthora colocasiae enlarged 100 times |
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| Raciborski , 1900 |
Phytophthora colocasiae is a species of egg fungus (Oomycetes) in the genus Phytophthora that causes aplant disease knownas taro leaf rot in taro .
description
Phytophthora colocasiae forms whitish, brownish, greyish flaky fungal lawns in so-called colonies . These colonies initially consist of a dense network of hyphae called the mycelium . The hyphae measure between 3 and 4 micrometers and are very variable in length.
The species reproduces in three different ways by vegetative reproduction , by asexual reproduction, and rarely by sexual reproduction .
Vegetative propagation
During vegetative reproduction, yellow chlamydospores with a diameter of 26–30 micrometers (in exceptional cases up to 39 μm) are formed. Your cell wall is up to 3 micrometers thick. The chlamydospores can be terminal or intercalary. When you germinate, 3-11 filaments form, which then form sporangia at their tips.
Asexual reproduction
During asexual reproduction, sporangiophores 2 to 4 micrometers long grow vertically out of the foot cell . These carry the stalked sporangia . In nature on taro leaves, the sporangiophores are short and unbranched. In culture they become longer and branch out irregularly with a swelling at the branching point. The sporangia are elongated ellipsoidal , sometimes almost spindle-shaped. They measure 45–60 × 23 micrometers (in exceptional cases up to 70 × 28 μm). The ratio of length to width is 1.6. The papilla protrudes slightly. The stem is thin and sloping. It is 3.5 to 10 micrometers long. The sporangium contains the mobile zoospores .
Sexual reproduction
Sexual reproduction in Phytophthora colocasiae is rare. Usually only in culture, oogonia with a diameter of 23 micrometers (in exceptional cases up to 35 μm) are formed in the female form , which turn yellow over time. The male form develops antheridia measuring 11–13 × 11 micrometers . These are mostly or completely amphigynous , that is, they completely enclose the stem of the oogonia. In the Oogonie then form Oospore with an up to 2.5 microns thick cell wall.
Pathogenicity
Phytophthora colocasiae attacks species of the genus Colocasia , especially taro ( C. esculenta ) and C. antiquorum . Also Alocasia macrorhiza is attacked, there is the fungus but due to lower inoculum not production epidemic . Tannia ( Xanthosoma sagittifolium ) is also affected.
Other farmers are reported to have elephant foot yam ( Amorphophallus paeoniifolius ), Bougainvillea spectabilis , Dracontium polyphyllum , the rubber tree ( Hevea brasiliensis ), American ginseng ( Panax quinquefolius ), betel ( Piper betle ), pepper ( Piper nigrum ), castor bean ( Ricinus communis ) and the pink catharanthe ( Catharanthus roseus ). However, many of these hosts have yet to be scientifically confirmed.
Taro leaf rot is caused in affected plants . Initially, small, dark, necrotic lesions form on the leaves. The lesions progressively enlarge and become moist. They are more or less round and initially purple before turning to brown. Often the lesions have concentric obscurations. In wet weather, a yellowish exudate flows from the lesions . The lesions are often stronger on the leaf margin than in the middle of the leaf. Eventually the leaf falls off. In the advanced stage, Phytophthora colocasiae also affects the leaf stalks and the rhizome . The disease causes severe harvest losses up to the total loss of the harvest.
distribution
Phytophthora colocasiae is widespread in South Asia and East Asia and parts of Oceania. In Asia, the species occurs in Myanmar, Sri Lanka, the People's Republic of China, Hong Kong, India, Java (Indonesia), in Japan, from the Malay Peninsula, in Nepal, Pakistan, Taiwan and Thailand. In Oceania, Fiji, Guam, Hawaii, Papua New Guinea, the Philippines, the Solomon Islands and Hawaii as well as the other US territories in the Pacific are affected.
Due to globalization, however, the species was able to spread further so in the 1970s, the first occurrences in the Dominican Republic and in Africa in Ethiopia and on Fernando Po were reported. From Ethiopia the species was able to spread further over East Africa. From Hispaniola to the United States (to California and North Carolina) as well as to Brazil and Argentina. The first cases occurred in Ghana in 2009 and Nigeria in November 2009. Much of the harvest in Cameroon was destroyed in the 2010 duck season. A further spread of the species in Africa and the Caribbean can be assumed.
literature
Unless otherwise stated, the information comes from this article:
- Paul Holliday: Fungal Diseases of Tropical Crops . Cambridge University Press, Cambridge 1980, ISBN 0-521-22529-9 , pp. 348-349 (English).
- Z. Gloria Abad: Phytophthora colocasiae. In: IDphy: Molecular and morphological identification of Phytophthora based on the types. US Department of Agriculture, January 29, 2018, accessed August 25, 2019 .
Individual evidence
- ↑ Davinder Singh, Grahame Jackson, Danny Hunter, Robert Fullerton, Vincent Lebot, Mary Taylor, Tolo Iosefa, Tom Okpul, Joy Tyson: Taro leaf blight — a threat to food security . In: Agriculture . tape 2 , no. 3 , 2012, p. 182–203 , doi : 10.3390 / agriculture2030182 (English).
- ↑ CAB International: Phytophthora colocasiae. [Distribution map] . ISSN 0012-396X (English, cabdirect.org ).
- ↑ E. Omane, KA Oduro, EW Cornelius, IY Opoku, AY Akrofi, K. Sharma, P. Lava Kumar, R. Bandyopadhyay: First Report of Leaf Blight of Taro (Colocasia esculenta) Caused by Phytophthora colocasiae in Ghana . In: Disease Notes . tape 96 , no. 2 , 2012, p. 292 , doi : 10.1094 / PDIS-09-11-0789 (English).
- ^ R. Bandyopadhyay, K. Sharma, TJ Onyeka, A. Aregbesola, PL Kumar: First Report of Taro (Colocasia esculenta) Leaf Blight Caused by Phytophthora colocasiae in Nigeria . In: Plant disease . tape 95 , no. 5 , 2011, p. 618 , doi : 10.1094 / PDIS-12-10-0890 (English).
- ↑ GA Mbong, CN Fokunang, Lum A. Fontem, MB Bambot, EA Tembe: An overview of Phytophthora colocasiae of cocoyams: A potential economic disease of food security in Cameroon . In: Discourse Journal of Agriculture and Food Sciences . tape 1 , no. 9 , 2013, ISSN 2346-7002 , p. 140-145 (English).