![Basipetalous [(opp: acropetalous) meaning tip to base]: formation of
matured conidia/sporangia from the tip to the base part of their production.
Isthumaus/disjunctor/separation disc – a gelatinous, disc-like structure
present on the walls of the sporangia that helps in connecting the
adjoining sporangia resulting in production of a chain of conidia. E.g
Albugo.
Indirect germination of sporangia - If water is available, sporangia
germinate indirectly that is sporangia produce zoospores inside and later
zoospores are released and they later germinate and infect the plants.
Direct germination of sporangia : if there is no water available, the
sporangia germinate directly producing germ tube and behave like condia
Why sporangia are called as conidia?
Because of direct germination in dry conditions, sporangium directly
germinate, produce germ tube and infect plant like conidia)](https://image.slidesharecdn.com/lect15-240305151056-de16b0dd/85/lect-15-pptx-insest-circulation-systems-bsc-7-320.jpg)
lect 15.pptx insest circulation systems bsc
- 1. Domain : Eukarya Kingdom: Chromista Oomycota Oomycetes Saprolegniales Sclerosporales Peronosporales Pythiales Saproleginaceae Peronosporaceae Albuginaceae Sclerosporaceae Verrucalvaceae Pythiaceae Saproleginia sp. Achyla sp. Aphanomyces sp. Peronospora sp. Pseudoperonospora sp. Plasmopara sp Bremia sp. Albugo sp. Sclerospora sp. Peronosclerospora Sclerophthora sp. Pythium sp. Phytophthora sp. sub class Class Saprolegniomycetidae Peronosporomycetidae Phyllum Albuginales
- 2. Albugo (syn:Cystopus) Domain: Eukarya Kingdom: Chromista Phylum: Oomycota Class: Oomycetes Sub class: Perenosporomycetidae Order: Albuginales Family: Albuginaceae Genus: Albugo Species: A. candida- Crucifer A. bliti- Amaranthus A. ipomaepanduranae (Convolvulaceae) A. tragapogonis (Compositae) A. occidentalis (spinach) A. portulaceae (Portulaca)
- 3. Terminologies Dimorphic zoospore (Opp: Monomorphic)- two different types of zoospores (differing in size/shape) produced in the life cycle of the fungus- Saprolegnia Diplanetism- Two types of zoospores are produced in the life cycle and each type swim for some time before they encyst – saprolegnia Plerotic oospore (Opp: aplerotic): Oospore completely fills the available space in the oogonium Aplerotic oospore: Oospore does not completely fill the Oogonium. There is a empty space between Oospore wall and Oogonium wall.
- 4. Host : crucifers-Cabbage, mustard, radish, turnip. Leafy vegetables -Amaranthus It causes two types of infection : Local and systemic Local infection: 1. Isolated white creamy pustules of 2-3 mm diameter size develop on the lower surface of leaves and stems. 2. Pustules merge to form larger patches. 3. Pustules are filled with sporangia and sporangiophores. Host epidermis ruptures after maturing of pustules. White Blister of crucifers / Amaranthus Albugo candida / A. bliti Systemic infection: 1. When young stems and flowering parts are infected it becomes systemic. Stimulates hypertrophy and hyperplasia which results in enlarged and variously distorted organ mostly flower parts. 2. Sepals become enlarged to several times than the normal sepals. 3. Petals enlarge and become green pistils and anthers are distorted. 4. Seed development is arrested.
- 5. Life cycle Fungal characters: 1. Thallus - The thallus is filamentous mycelium. Mycelium is hyaline, coenocytic and intercellular, absorbs nutrients through haustorium 2. Parasitism - It is an obligate biotroph 3. asexual reproduction - during asexual reproduction, mycelium aggregates below the epidermis. Mycelium differentiates and gives rise to club shaped unbranched sporangiophore which bears sporangia in basipetal chain. Sporangia are held together in chain by Isthumaus/disjunctor/separation disc. Sporangia germinate directly/indirectly. Zoospores –Biflagellate, reniform 4. Sexual reproduction – produces Anthredium and Oogonium and gametangial contact type of plasmogamy. Sexual spores- Oospores
- 6. Asexual reproduction: 1. during asexual reproduction, mycelium aggregates below the epidermis. Mycelium differentiates and gives rise to club shaped unbranched sporangiophore which bears sporangia in basipetal chain. Each sporangium is attached with others by a gelatinous substance called Isthumaus/disjunctor/separation disc. Sporangia push the epidermis and rupture ultimately resulting in white mass of sporangia that gives white pustules. 2. Zoospore are produced and released from sporangium. They swim for some time and after swimming period, encyst and germinate and produce germ tube which enters the host tissue and produce intercellular mycelium 3. Sporangia causes secondary spread and infection. 4. Sporangium germinates both directly and indirectly. Sexual reproduction 1. It is through gametangial contact (Plasmogamy) with paragynous antheridium. The sexual spore is Oospore which is ornamented. 2. Sexual reproduction take place when crop matures. Hyphae penetrate deeper into the tissue and form the gametangia (male- antheridium and female- Oogonium). 3. The onset of sexual reproduction is usually indicated by hypertrophy of the infected parts. 4 Meiosis occurs just before the formation of gametes (nuclei) in the gamatagium 5. Plasmogamy- gametantial contact. Antheridium is paragynous 6. Karyogamy leads to diploid oospores 7. Oospore germinate and gives zoospores
- 7. Basipetalous [(opp: acropetalous) meaning tip to base]: formation of matured conidia/sporangia from the tip to the base part of their production. Isthumaus/disjunctor/separation disc – a gelatinous, disc-like structure present on the walls of the sporangia that helps in connecting the adjoining sporangia resulting in production of a chain of conidia. E.g Albugo. Indirect germination of sporangia - If water is available, sporangia germinate indirectly that is sporangia produce zoospores inside and later zoospores are released and they later germinate and infect the plants. Direct germination of sporangia : if there is no water available, the sporangia germinate directly producing germ tube and behave like condia Why sporangia are called as conidia? Because of direct germination in dry conditions, sporangium directly germinate, produce germ tube and infect plant like conidia)
- 8. Domain : Eukarya Kingdom: Chromista Oomycota Oomycetes Saprolegniales Sclerosporales Peronosporales Pythiales Saproleginaceae Peronosporaceae Albuginaceae Sclerosporaceae Verrucalvaceae Pythiaceae Saproleginia sp. Achyla sp. Aphanomyces sp. Peronospora sp. Pseudoperonospora sp. Plasmopara sp Bremia sp. Albugo sp. Sclerospora sp. Peronosclerospora Sclerophthora sp. Pythium sp. Phytophthora sp. sub class Class Saprolegniomycetidae Peronosporomycetidae Phyllum Albuginales
- 9. Downy mildew (downy=hairy; mildew= fungal growth) Sporangiophores emerge in group through stomata and looks like hairs. This forms a visible mat of downy (hairy) growth on the lower surface of the leaves. That is why the name of the disease is called Downy mildew. At the end of the sporangiophores, sporangia are produced. Downy growth comprising of sporangiophores and sporangia is the major sign of the disease. Downy mildew disease- hairy fungi
- 10. DOWNY MILDEW DISEASE- peronosporales crops Causal organism Sporangiophore characters grapes Plasmopara viticola branched at Right angle crucifers- Peronospora parasitica Dichotomously branched at acute angle, tapers to fine points Peronospora – bears conidia Pseudoperonospora- sporangia cucurbits Pseudoperonospor a cubensis Bremia (lettuce) Dichotomously branched, terminates in disc (saucer) like structure bearing sporangia on sterigmata basidiopora Sporangiophore is basidium like club shaped, unbranched sporangiophores, sporangium are produced on the tip of the sterigmata sorghum Peronosclerospora sorghi Swollen , Short, upright branches bearing sporangia Peronosclerospora –conidia Sclerospora sporangia maize Sugarcane Peronosclerospora sorghi Peronosclerospora sachhari Cumbu- Sclerospora graminicola Distinguishing/characteristic features of sporangiophores of downy mildew fungi The genera of the downy mildew fungi are identified based on their sporangiophores morphology
- 11. Sorghum downy mildew: Peronosclerospora sorghi Symptoms: 1. The infected plants become stunted. 2. The systemically infected seedlings show whitish soft downy growths mainly on the lower surface of the leaves. There is a corresponding pale yellowish discolouration on the upper surface. The infected plants show streaks on surfaces of the upper leaves. 3. Owing to formation of oospores, necrosis of tissues occur and the streaks turn brown. They then tear along the veins producing the characteristic symptom of leaf shredding. The thick walled, deep brown, spherical oospores arranged linearly in between the veins of shredded leaves. leaf shredding oospores
- 12. Fungal characters: 1. Thallus - The mycelium is filamentous inter-cellular, hyaline, non-septate, branched, produce haustorium 2. Parasitism- Biotrophs 3. Asexual - The sporangiophores emerge through stomata singly or in clusters, they are swollen , Short, upright branches bearing sporangia . Zoospores – biflagelate longer tinsel flagellum directed forward and a shorter whiplash flagellum directed backward 4. Sexual reproduction - Plasmogamy- Gametangial contact, Oospores – sexual spores
- 13. Maize downy mildew: Peronosclerospora sorghi Symptoms: 1. The most characteristic symptom is the development of chlorotic streaks on the leaves. White downy growth seen on the lower surface of leaves. 2. Tassels are converted into green leafy structures known as “Crazy top” symptom. Leaf symptom Crazy top
- 14. Downy mildew or Green ear of Cumbu/ Bajra / Pearl millet: Sclerospora graminicola Symptoms: Two stages (i) Downy mildew stage (ii) Green ear stage (i) Downy mildew stage 1. The disease starts with systemic infection of young seedlings. The affected seedlings are very much stunted and pale yellow in colour. 2. There will be excessive tillering. 3. The leaves exhibit pale chlorotic streaks on the upper surface. 4. Profuse downy white growth consisting of sporangiophores and sporangia of the pathogen occurs predominantly on the lower surface of the leaves. 5. As the disease advances the streaks turn brown and shredding of leaves occurs along the veins. More lateral shoots are formed giving bushy appearance. The infected seedlings may die within 30 days.
- 15. (ii) Green ear stage In many affected plants, no ears formed. If formed they are either partially or fully malformed into green leafy structure hence the name green ear disease. Then they become brown and dry. Downy mildew or Green ear of Cumbu/ Bajra / Pearl millet: Sclerospora graminicola
- 16. Downy mildew of crucifers - Peronospora parasitica Symptoms: White fluffy fungal growth on leaves, stems, seed pods. Later become small, purplish irregular areas The systemically invaded tissue turns yellowish and become necrotic, dries out Cabbage seed pods twist, curl and break opens to expose the seeds
- 17. Downy mildew of grapes - Plasmopara viticola Symptoms: 1. Downy mildew affects the leaves, tendrils, flowers, fruits and vines. 2. The disease is first observed as small translucent, pale yellow spots on the upper surface of leaves. 3. On the corresponding under surface, a downy growth appears, later, the infected areas turn brown. During blossom or early fruiting stages, entire clusters or parts of them are covered with downy growth and die. 4. If infection takes place after the berry stage, they become leathery wrinkled and mummified.
- 18. Fungal characters: 1. It is an obligate biotroph 2. The thallus (body) is filamentous mycelium. Mycelium is hyaline, coenocytic and intercellular and absorbs nutrients through haustorium 3. Sporangiophores produce 4-6 monopodial primary branches at right angles to the main axis. Each branch form 3 secondary branches at right angles. From the apex of each branch 2-3 sterigmata arise and bear sporangia, which are thin walled and oval with papilla at the tip. 4. Oospores are thick walled and germinate by producing a germ tube that bears an apical sporangium.