Site pages
Current course
Participants
General
Topic 1
Topic 2
Topic 3
Topic 4
Topic 5
Topic 6
Topic 7
Topic 8
Topic 9
Topic 10
Topic 11
Topic 12
Topic 13
Topic 14
Topic 15
Topic 16
Topic 17
Topic 18
Topic 19
Topic 20
Topic 21
Topic 22
Topic 23
Topic 24
Topic 25
Topic 26
Topic 27
Topic 28
Topic 29
Topic 30
Topic 31
Topic 32
Topic 33
Topic 34
Topic 35
Topic 36
Topic 37
Topic 38
Topic 39
Topic 40
Topic 41
Topic 42
Topic 43
Topic 44
Topic 45
Topic 46
Topic 47
Topic 48
Topic 49
Topic 50
DISEASES CAUSED BY PYTHIUM SPP
Exercise 1: DISEASES CAUSED BY PYTHIUM SPP. |
a) Damping-off of vegetables (Causal organism: Pythium aphanidermatum (Edson) Fitz.) Kingdom : Chromista Division : Eumycota Phylum : Oomycota Class : Oomycetes Order : Peronosporales Family : Pythiaceae Genus : Pythium Species : aphanidermatum Symptoms: The disease manifests at two phases: Pre-emergence damping-off: Seed rots or young seedlings are killed before their emergence from the soil resulting in patchy appearance of seedlings stand in the nursery . Post-emergence damping-off: The infected tissue of stem at soil level initially appears to be water soaked and soft, subsequently, the stem at the infection point gets constricted resulting in toppling over and mortality of the seedlings. b) Soft rot of ginger (Causal organism: Pythium aphanidermatum (Edson) Fitz.) Symptoms: Leaves turn yellow. The yellowing starts from leaf tip and spreads down the leaf blade. The dead leaves hang down. Tillers at soil line become soft and later topples down. The rhizomes become soft and mushy. Roots also rot. Mycelium: Well-developed, branched, coenocytic, hyaline, intracellular, without haustoria. Asexual reproduction: Sporangium much lobed, toruloid, branched, produced only in liquid culture, formed terminally or intercalary on somatic hypha. Zoospores produced in vesicle (Fig. 1), which emerged out of sporangium. Sexual reproduction: Oogamous, by gametangial contact, oospores smooth, thick walled, round (Fig. 1) and light brown. Fig 1. Microscopic details of Pythium |
Last modified: Thursday, 22 December 2011, 6:21 AM