Brown rust of the wheat
| Brown rust of the wheat | ||||||||||||
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Brown rust of wheat ( Puccinia triticina ) |
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| Puccinia triticina | ||||||||||||
| Erikss. |
The brown rust of wheat ( Puccinia triticina ) is a representative of the rust fungi (Pucciniales) and is also an important harmful fungus on wheat crops in Central Europe . Like all rust fungi, brown rust is an obligatory parasite .
Hosts
Seen worldwide, the most important main host is common wheat ( Triticum aestivum ). Brown rust is also found on durum wheat ( Triticum durum ), wild emmer ( Triticum dicoccoides ) and domesticated emmer ( Triticum dicoccon ). In Israel there is brown rust on Aegilops speltoides , in the USA on Aegilops cylindrica .
Thalictrum species serve as intermediate hosts , especially Thalictrum speciosissimum in southern Europe . Isopyrum fumaroides only serves as an intermediate host in Siberia.
Features and life cycle
Brown rust has the complete life cycle of rust fungi with five types of spores and two different hosts.
The binuclear uredospores are formed in spore beds of around 1.5 mm in diameter and orange to brown in color, which are formed on both leaf sides of the wheat. The uredospores are approximately spherical, orange-brown, have a diameter of about 20 micrometers and up to eight germ pores, which are scattered in the thick, prickly wall. In the presence of liquid water and temperatures between 10 and 25 ° C, the uredospores can in turn attack the wheat.
When the wheat ripens, the fungus forms binuclear, brownish-black, two-celled teliospores that are 16 micrometers in size and have thick, smooth cell walls. The teliospores are formed in the uredospore beds. In their Mediterranean home, the teliospores survive the dry, hot summer and attack the intermediate host in autumn. In the teliospore, the two nuclei of a cell fuse to form a diploid cell nucleus . Under favorable conditions, the teliospore germinates into a so-called promycelium. The nuclei go through a meiosis , the four haploid nuclei migrate into the promycelium, the formation of cell walls results in four cells, each of which forms a protuberance (sterigma) into which the cell nuclei migrate and thus form basidiospores .
After another nucleus division, the mature basidiospore is around 6 micrometers in size, single-celled with two identical haploid cell nuclei. The basidiospores are ejected and infect epidermal cells at the intermediate host. Here they form bottle-shaped pycnidia , which appear as yellow-orange pustules on the leaf surface. The pycnidia form haploid pycnospores that are 2 to 3 micrometers in size. Furthermore, they form hyphae that function as male and female gametes . The brown rust is heterothallic, that is, pycnospores and receiving hyphae from the same pycnidia are not compatible. The pycnospores are located in a nectar-like exudate that attracts insects, which cause it to spread. Fertilization takes place when a pyknospore fuses with a receiving hypha, creating a binuclear mycelium. This mycelium spreads in the host leaf and forms aecidia on the underside of the leaf, usually directly below the pycnidia on the upper side of the leaf.
The aecidiospores formed in the aecidia are binuclear, 20 micrometers in size and are formed in chains. The wind spreads it. If an aecidiospore reaches a main host, it germinates, penetrates the host through a cleft opening and thus completes the cycle.
However, the brown rust can only multiply indefinitely via the asexual uredospores and is not dependent on the presence of the intermediate host. Overwintering takes place in winter wheat, provided the temperatures are not too low.
Taxonomy
The brown rust of wheat was first described by Augustin-Pyrame de Candolle in 1815 under the name Uredo rubigo-vera , from winter 1884 then placed as Puccinia rubigo-vera in the genus Puccinia , where it is due to its two-celled teliospores to this day. Eriksson was the first to describe wheat brown rust under the name Puccinia triticina , which is valid today . Cummins and Caldwell combined the species in 1956 on a morphological basis with other brown rusts under the name Puccinia recondita f. sp. triticina . In the last few years the view has gained acceptance that the forms that Thalictrum speciosissimum have as an intermediate host must be delimited as a separate species. This is based on sexual incompatibility, rDNA sequence analyzes, spore morphology and infection structure morphology. In the meantime, the name Puccinia triticina described by Eriksson is largely used again .
meaning
The brown rust can lead to significant harvest losses worldwide. In 2007, he cut the harvest in the USA's most important wheat-growing state, Kansas , by 14%. The losses result from a lower number of grains per ear and a lower grain weight.
supporting documents
- Melvin D. Bolton, James A. Kolmer, David F. Garvin: Wheat leaf rust caused by Puccinia triticina . Molecular Plant Pathology, Volume 9, 2008, pp. 563-575. doi : 10.1111 / J.1364-3703.2008.00487.X
Web links
- Wheat leaf rust at Agricultural Research Service.