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Peronospora
Genus of plant pathogens From Wikipedia, the free encyclopedia
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Peronospora is a genus of downy mildews that are obligate plant pathogens.[1] They can cause severe damage to many different cultivated crops, as well as wild and ornamental plants.[2] Peronospora is most closely related to Pseudoperonospora, and together they form the clade of downy mildews with coloured conidia.[3] Peronospora has far more species than any other genus of the downy mildews.[3] However, many species have been moved from this genus to other genera based on phylogenetic evidence.[4] Among these are the species now in Hyaloperonospora, important pathogens of the Brassicaceae.[4] Now, the Peronospora species of most importance is likely Peronospora tabacina.[5][opinion] Peronospora tabacina causes blue mold on tobacco plants and can severely reduce yields of this economically important crop to the point where it has been classified as a bioweapon.[5][3]
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History
Peronospora was first described in 1837 by August Carl Joseph Corda, a Czech mycologist and physician, in his first of six volumes of his Icones fungorum hucusque cognitorum.[6] Since then, many of the species originally placed in Peronospora have been allocated to other genera or given rise to new genera based on new techniques such as molecular genetics.[4]
There was an epidemic in 1960 of Peronospora tabacina affecting tobacco plants leading to $25 million in losses across eleven countries, which was about 30 percent of the tobacco plants.[5] Another epidemic that was caused by Peronospora destructor reduced the yield of sweet onions by 25 percent in Georgia, USA in 2012, and led to an estimated $18.2 million in losses.[7]
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Habitat and ecology
Most of the Peronospora species are highly specific to their hosts and can generally be found anywhere the host plant grows, or is being cultivated.[3] A large portion of their life cycle is spent inside their host plant. Many species of Peronospora are seedborne pathogens, so the worldwide spread of Peronospora crop-plant pathogens is likely to be a result of unknowingly trading infected seeds to new areas.[3] There are also many Peronospora species that are spread by wind currents, which allows them to disperse over large distances.[3] Peronospora species prefer humid air and cool temperatures.[5]
One clade in the genus is known as the floricolous downy mildews. These species produce conidiophores exclusively on the flowers of their hosts.[8]
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General form and structure
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The first stage in the Peronospora life history is the sporangia.[5] The sporangia are small spore-like structures about 65 um long that germinate a germ-tube when they are near a leaf stoma.[9][5] A germ tube will come from the sporangium and penetrate the leaf cell where it will form a haustorium.[5] The haustorium absorbs nutrients from the leaf, while hyphae invade the intercellular space, and the leaf will eventually develop a lesion.[5] These lesions often start out yellow and then turn brown as the leaf starts to undergo necrosis.[5] From here, Peronospora can undergo either asexual reproduction or sexual reproduction.[5] Asexual reproduction occurs when the air outside is moist making for favourable conditions.[5] During asexual reproduction, hyphae on the host plant will form sporangiophores, which will produce conidia.[5] The conidia will be dispersed by the wind is able to infect other plants.[5] The asexual cycle only takes five to seven days to complete.[5] Sexual reproduction occurs when the conditions are unfavourable and it needs to withstand harsh environmental conditions.[5] During sexual reproduction, the hyphae will undergo meiosis forming antheridia and oogonia, the only haploid structures in the Peronospora life history.[5] The antheridia will fuse to the oogonia, initiating plasmogamy and then karyogamy, and will result in the production of many oospores.[5] The oospores can then be dispersed by the wind to infect more plants.[5]
Both Peronospora and Pseudoperonospora are characterized by their ability to produce melanized sporangia, but Pseudoperonospora produces zoospores whereas Peronospora cannot.[3]
Practical importance
The model oomycete pathogen, Peronospora parasitica, used to be included in this genus, however it has been reclassified to the genus Hyaloperonospora.[3]
Some species of Peronospora have been considered for their use as a bioweapon or have been classified as potential bioweapons.[3] Peronspora somniferi was considered for its ability to devastate fields of the opium poppy, which could have targeted areas that depend on the crop.[3] The United States has classified Peronospora tabacina as a possible bioweapon, because if it were used to target the US tobacco industry, it would lead to major economic loss.[3]
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Genomics and genetics
Only one species in the genus Peronospora has had its genome sequenced and assembled. In 2015, Derevnina et al. performed a de novo sequence assembly of the genome of two Peronospora tabacina isolates using Illumina sequencing.[10] They estimated the genome size to be 68 Mb with a mitochondrial genome of 43 kb.[10] The two assemblies had 61.8x and 128.9x coverage for the nuclear genomes and 6,824x and 43,225x coverage for the mitochondrial genomes.[10] The mitochondrial genome only differed by seven single nucleotide polymorphisms, three small indels, and one copy number variant.[10] Using a program to predict gene models, they found 18,000 potential protein coding genes.[10]
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List of species
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The following species are placed in genus Peronospora:[11]
- Peronospora aconiti
- Peronospora aestivalis
- Peronospora affinis
- Peronospora agrestis
- Peronospora agrimoniae
- Peronospora alchemillae
- Peronospora alpicola
- Peronospora alsinearum
- Peronospora alta Fuckel
- Peronospora akatsukae Ito & Murayama
- Peronospora anagallidis
- Peronospora antirrhini
- Peronospora aparines
- Peronospora apula
- Peronospora aquatica
- Peronospora arborescens
- Peronospora arenariae
- Peronospora argemones
- Peronospora arthurii
- Peronospora arvensis
- Peronospora asperuginis
- Peronospora astragalina
- Peronospora atriplicis-hastatae
- Peronospora belbahrii
- Peronospora boni-henrici
- Peronospora bulbocapni
- Peronospora calotheca
- Peronospora campestris
- Peronospora canescens Benua
- Peronospora cerastii-anomali
- Peronospora cerastii-brachypetali
- Peronospora chenopodii-polyspermi
- Peronospora chlorae
- Peronospora chrysosplenii
- Peronospora claytoniae
- Peronospora conglomerata
- Peronospora consolidae
- Peronospora coronillae
- Peronospora corydalis
- Peronospora corydalis-intermediae
- Peronospora cristata
- Peronospora cyparissiae
- Peronospora debaryi
- Peronospora destructor
- Peronospora dianthi
- Peronospora dianthicola
- Peronospora dicentrae
- Peronospora digitalis
- Peronospora dipsaci
- Peronospora echii
- Peronospora effusa
- Peronospora elsholtziae
- Peronospora erodii
- Peronospora ervi
- Peronospora esulae
- Peronospora farinosa
- Peronospora farinosa f. sp. betae
- Peronospora farinosa f. sp. chenopodii
- Peronospora farinosa f. sp. spinaciae
- Peronospora ficariae
- Peronospora flava
- Peronospora fulva
- Peronospora galii
- Peronospora glechomae
- Peronospora grisea
- Peronospora hiemalis
- Peronospora holostei
- Peronospora honckenyae
- Peronospora illyrica
- Peronospora jagei
- Peronospora knautiae
- Peronospora kochiae-scopariae
- Peronospora lamii
- Peronospora lapponica
- Peronospora lathyri-verni
- Peronospora lathyrina
- Peronospora lepigoni
- Peronospora linariae
- Peronospora linariae-genistifoliae
- Peronospora lithospermi
- Peronospora litoralis
- Peronospora lotorum
- Peronospora manshurica
- Peronospora mayorii
- Peronospora meconopsidis
- Peronospora medicaginis-minimae
- Peronospora medicaginis-orbicularis
- Peronospora melandryi-noctiflori
- Peronospora meliloti
- Peronospora mesembryanthemi
- Peronospora minor
- Peronospora myosotidis
- Peronospora narbonensis
- Peronospora oblatispora
- Peronospora obovata
- Peronospora ornithopi
- Peronospora orobi
- Peronospora parva
- Peronospora paula
- Peronospora perillae
- Peronospora phacae
- Peronospora plantaginis
- Peronospora polycarpi
- Peronospora polygoni
- Peronospora polygoni-convolvuli
- Peronospora potentillae
- Peronospora potentillae-anserinae
- Peronospora potentillae-reptantis
- Peronospora potentillae-sterilis
- Peronospora pseudostellaria
- Peronospora pulveracea
- Peronospora radii
- Peronospora ranunculi
- Peronospora aff. ranunculi
- Peronospora romanica
- Peronospora rubi
- Peronospora rumicis
- Peronospora salviae-plebeiae
- Peronospora sanguisorbae
- Peronospora saturejae-hortensis
- Peronospora saxifragae
- Peronospora schachtii
- Peronospora scleranthi
- Peronospora scutellariae
- Peronospora sepium
- Peronospora sherardiae
- Peronospora silvatica
- Peronospora silvestris
- Peronospora somniferi
- Peronospora sordida
- Peronospora sparsa
- Peronospora stachydis
- Peronospora statices
- Peronospora stellariae-aquaticae
- Peronospora stellariae-uliginosae
- Peronospora stigmaticola
- Peronospora swinglei
- Peronospora symphyti
- Peronospora tabacina
- Peronospora tetragonolobi
- Peronospora teucrii
- Peronospora tomentosa
- Peronospora tranzscheliana
- Peronospora trifolii-alpestris
- Peronospora trifolii-arvensis
- Peronospora trifolii-hybridi
- Peronospora trifolii-minoris
- Peronospora trifolii-repentis
- Peronospora trifoliorum
- Peronospora trifoliorum f. trifolii-pratensis
- Peronospora trigonellae
- Peronospora trigonotidis
- Peronospora trivialis
- Peronospora valerianae
- Peronospora valerianellae
- Peronospora variabilis
- Peronospora verbasci
- Peronospora verbenae
- Peronospora verna
- Peronospora vernalis
- Peronospora viciae
- Peronospora viciae f. sp. pisi
- Peronospora violacea
- Peronospora violae
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References
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