Unit 3 Fungal Plant Panthogens.docx

1、Unit 3 Fungal Plant PanthogensFungal Plant PathogensIntroduceFungi are spore-forming，non-chlorophytic，eukaryotic(cells having true nuclei)organisms and most of the true fungi are filamentous and branchedMost of the over 100，000 species of fungi are saprophytesHowever，over 20，000 species of fungi are

2、 parasites and cause disease in crops and plantsFungal parasites are by far the most prevalent plant pathogenic organism All plants are attacked by one species or another of phytopathogenic fungiIndividual species of fungi Can parasitize one or many different kinds of plants Hyphae myceliumThe body，

3、or thallus，of most of the higher fungi is called a mycelium(plmycelia)The mycelium is made up of thread-like structures called hyphaeHyphae grow only from their tips，and under favorable conditions Can grow indefinitelyHyphae，most often，are partitioned by cross walls called septaSeptate hyphae are di

4、vided into individual cells by these internal wallsSepta usually have a central pore which allows small organelles， and in some cases nuclei，to pass from one cell to anotherThe hyphae of the classes Ascomycetes，Basidiomycetes and Deuteromycetes are septate and the hyphae of class Oomycetes and zygom

5、ycetes ale nonseptate or coenocyticCoencytic hyphae have multiple nuclei in a common cytoplasm Hyphae produce specialized simple or branched projection called haustoria. Haustoria penetrate the host tissue and act as nutrient absorbing organs.Haustoria contain nuclei and a concentrated number of mit

6、ochondriaThe haustoria do not rupture the host cell protoplasmic membrane but invaginates itself into the cell thus greatly increasing the absorptive surface of the fungus Reproduction of fungi is primarily by means of sporesSpores are reproductive bodies that consist of one or a few cellsIn functio

7、n they are anMogous to the seeds of green plantsSpores ago produced by sexual and asexual reproductionSexual reproduction involves the union of tWO compatible nuclei as produced by meiosisFor many phytopathogenic fungi the sexual cycle occurs only once during each growing seasonSexually produced spo

8、res include oospores，zygospores，ascospores and basidiospores characteristic of the phyla Oomycota，Zygomycota，Ascomycota and Basidiomycota respectivelyAsexual reproduction usually occurs by means of mitosis which produce mitotic spores，mycelial fragmentation，fission and buddingWith asexual reproducti

9、on the repeating cycles of infection can continue throughout the growing seasonAsexual spores may be classified as oidia(formed by fragmentation of hyphae into individual cells)，conidia(borne on tips or sides of specialized branches of hyphae)and sporangiospores(a nonmotile spore bom in a sporangium

10、 or case)There are many types and different characteristics of fruiting bodies， spores and mycelinmFungi are both classified and identified by these featuresThe classification of pathogenic fungi is important for identifying and diagnosing plant diseaseEach kingdom，phylum，class，order，family，genus an

11、d species has its own identifying characteristicsMany of the diagnostic factors in identifying different fungi are very subtle and without proper lab equipment and skill are difficult to identify down to the species levelIf we can identify thetype of fruiting body andor spores that are associated wi

12、th a particular phylum，we can narrow down our search considerablyMost often，we rely on visual signs and symptoms for diagnosis of fungal diseasediseaseThe primary phyla dealt with in plant pathology and disease diagnosis are listed belownlis outline is very brief and only includes a few of the more

13、important pathogens and problemsAlso included are some of the more important characteristics of each phylumFor further clarification on fungal taxonomy，you can refer to any number of resources at the Extension officeAlso，the internet is an excellent source of information on this subject.cellent sour

14、ce of information on this subjectFungal-like organisms(lower fungi)： Kingdom：Protozoa Phylum：Plasmodiophoromycota(endoparasitic slim molds)eg，： Plasmodiophora brassicae，causing club root of crucifers Spongosphora subterranean，causing powdery scab of potato tubers Kingdom：Chromista Phylum：Oomycota(bi

15、flagellate zoosporesSimple pored nonseptate hyphaeAsexualsporessporangiospores，motile and nonmotileSexual sporeszoospores)eg，：chrysanthemum white rust，Phytophthora sspdiseases，downey mildew.True Fungi： Kingdom：Fungi Phylum：Chytridiomycota(zoospores，lack true mycelium)eg,：parsitic on roots ofcabbage

16、and many other plants. Phylum:Zygomycota(saprophytes or parasites of plants, Humans and animals. No zoospores. Simple pored nonseptate Hyphae. Asexual spores-Sexual nonmotile sporangiispores.)e.g.,: Rhizopus-bread molds,rots of fruits and vegetables. Phylum:Ascomycotathe sac fungi-most have both tel

17、eomorphic (sexual) and anamophic (asexual)stages. Simple septate hyphae. Produce sexual spores(ascospores) or asexual spores (conidia) on free hyphae or in asexual fruiting bodies such as Cleistothecium, Perithecium, Apothecium and Pycnidium. This phylum is responsible for most of our phytopathogeni

18、c fungal diseases. Class:Deuteropmycetes(Mitosporic or imperfect fungi-also known as Fungi Imperfecti. Sexual reproduction and structures are rare, lacking or unknown. Simple septate hyphae with some exceptions. Asexual spores-condia produced in pycnidia and acervuli ). This class is responsible for

19、 many rots, wilts, molds, leaf, spots and other symptoms. Phylum: Basidiomycota(club and mushroom fungi)-complex septate hyphae, clamp connections. Asexual spore-conidia, oidia. Sexual spores-basidiospores produced externally on club-like spore producing structure called basidium. Diagnostic Signs a

20、nd Symptoms of Fungal Infection Fungi can cause general or localized signs andor symptomsIn the majority of cases，fungal infections cause general necrosis of host tissue and often cause stunting，distortions and abnormal changes in plant tissue and organsThe most distinctive and easily identifiable c

21、haracteristics of fungal infections are the physical presence of signs of the pathogenSigns include hypha，mycelia，fruitings，bodies and spores of the fungal pathogen are significant clues to proper identification and diagnosis of a diseaseThe fruiting bodies of fungi range from microscopic to macrosc

22、opicThey come in many shapes and configurations and have their individual characteristicsThe fruiting bodies，along with spores，and mycelium，inmost cases can lead to an accurate identification of the diseaseThe following symptoms are common in fhngal infections whether alone or in combination with ot

23、her fungal pathogens Leaf spots are very common in both biotic and abiotic plant disordersFungal leaf spots often take the form of locahzed lesions consisting of necrotic and collapsed tissueLeaf spots can vary in size and are generally round and concentric，but can be ovoid or elongated on both leav

24、es and stems of the hostThe typical fungal leaf spot will have a“bulls-eye-like”appearance consisting of roughly concentric tings that may display zones of different colors such as yellow，red or purple，and will often have a tan centerAs the spots develop，they are not restricted by the leaf veins as

25、can be the case in bacterial 1eaf spotsFungal leaf spots will usually have a dry texture but are not dry and papery Bull huss eye bulls eye beatys eyeOther common symptoms of fungal infections can be： Anthracnose：an ulcer-like lesion that can be necrotic and sunkenThese lesions can appear on the fru

26、it，flowers and stems of the host-e.g.，Apple anthracnose of stems and or leaves(Cryptosporiopsis spformally Pezicula sp)，or dogwood anthracnose(Discula distructiva) Canker：a localized necrotic lesion on woody tissue，often sunken-eg，Apple European canker(Nectria galligena)，Douglas fir，upper Twig Canke

27、r(phomopsis sp)，and many moreDamping off：a rapid collapse and death of very young seedlingEither the seed rots beforeemergence or the seedling rots at the soil line and falls over and diesSeveral soil-born fungi cause this diseaseThe most common genera involved ale Fusarium，Rhizoctonia and Pythium S

28、cab：localized lesion on host fruit leaves tubers and other plant partsThese infections usually result in a roughened，crust-like alea on the surface of the host-e。g，Apple scab(Venturia inaequalis) and peal scab(Venturia pirina)Scab of potato Soft and dry root rots：rot and disintegration of fleshy lea

29、ves，roots，tubers and fruit-eg，Damping off of seedlings，Rhododendron，Phytophthora Root rot(Pcinnamomi)，Armaillaria sppRoot rot of trees and hundreds of other plants Blight: rapid generalized browning and death of leaves， floral organs， stems and branchesBlights Can refer to both biotic and abiotic di

30、sorders-eg，Cherry brown rot，blossom blight(Monilinia fructcola and M.laxa)，tomato early blight(Alternaria tomatophilai，formally，Asolani)and tomato and potato late blight(Phytophthora infastans)P.infestans was responsible for the great potato famine in Ireland in 1845Dieback：progressive death of shoo

31、ts and twigs generally starting at the tip of the infected plant part-e-g，Shoot dieback of apple due to cherry brown rot(Monilinia sp.)and poplar shoot dieback(Venturia populina)Bacteria are probably more commonly associated with diebacks(Pseudomonas synngae) Decline：progressive loss of vigor over a

32、 period of timeGeneral decline can be caused by many factors including fungal，bacterial， environmental and other factors，usually in combination Other symptoms associated with excessive growth(hyperplasia)or enlargement(hypertrophy)and distortion of plant parts can be demonstrate by the following:and distortion of plant parts Can be demonstrated by the following： Galls：enlarged parts of plant organs，usually caused by excessive multi