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Advances in the morphological and molecular identification of Pythiogeton species
Z. Gloria AbadUSDA-APHIS-PPQ-PSPI, Beltsville, MD, USA
Motoaki TojoOsaka Prefecture University, Sakai, Osaka, Japan
Cytoplasm evacuation of sporangium of Pythiogeton
Background and objectives1. Pythiogeton in the Kingdom Straminipila with
it's only nine species is a not widely studied genus.
2. In the USA, P. ramosum (Minden 1916) and P. autosytum (Drechsler 1932) have been reported.
3. Three putative new Pythiogeton species were isolated from ornamental plants (cypress, English-ivy and alyssum) which showed root rot symptoms during the summer 2003 in NC, USA.
4. These Pythiogeton species were characterized on morphology and the ITS rDNA sequences.
Kingdom: StraminipilaPhylum: HeterokontaClass: PeronosporomycetesOrder: PythialesFamily: PythiaceaeGenus: Pythium
PhytophthoraHalophytophthoraPythiogeton
Patterns of sporangium development in Pythiaceae
Cysts
Zoospores
Vesicle
Sporangium
Flagellum synthesis
&Cytoplasmic
cleavage
Flagellum synthesis
&Cytoplasmic
cleavage
Flagellum synthesis
&Cytoplasmic
cleavage
Pythium Phytophthora,Halophytophthora
Pythiogeton
Clear Non or UnclearNon or Unclear
0:30
1:30 2:00
0:00
3:00
4:00 5:00
1:00
18:00
Zoospore development inPythiogeton sp. 1
Bars = 20μm
0:00 0:10 0:20
0:30 0:40 0:50
0:60 1:20 2:00
Zoospore development inPythiogeton sp. 3
Bars = 20μm
Sporagium of Pythiogeton sp. 1produced in water culture
Sporagium of Pythiogeton sp. 1 produced in radish root hairs. No obvious symptom was observed
1
2 3 4
5 6
10
9
8
7
11 12
1-5. Sporangia
6. Appressoria
7, 8. Cytoplasm evacuation and zoospore development through vesicles (arrowhead)
9. Zoospore with flagella
10. Encysted and germinated zoospores
11. Sporangia formed in cypress roots after artificial inoculation (arrow heads)
12. Sporangia formed around cypress roots after artificial inoculation
Bars: 1-10 = 20 µm
Bars: 11, 12 = 50 µm
Morphology of Pythiogeton sp. 1
22
23
24
26
25
27
28
30
31 32 33
29
22-25. Sporangia
26. Appressoria
27, 28. Development of zoospores out and inside of sporangia
29. Empty sporangium with a vesicle (arrowhead)
30. Encysted zoospores
31-33 Sporangia formed in and around English Ivyroots after artificial inoculation
Bars: 22-30 = 20 µm
Bars: 31-33 = 50 µm
Morphology of Pythiogeton sp. 2.
34
35
36 37
38
39
40
41
42
43 44
34-39. Sporangia
40. Appressoria
41. Empty sporangium with vesicle (arrowhead)
42. Encysted and germinated zoospores
31-33 Sporangia formed in and around root of Alyssum roots after artificial inoculation
Bars: 34-42 = 20 µm
Bars: 43, 44 = 50 µm
Morphology of Pythiogeton sp. 3
0.1
P.arrhenomanes.39
P.volutum.64P.vanterpoolii.61
P.periilum.54P.graminicola.29
P.inflatum.63
P.aphanidermatum.71P.deliense.42
P.porphyrae.06P.destruens.74
P.insidiosum.64P.grandisporangium.91Pythiogeton.English.Ivy.03.287
Pythiogeton.Cypress.02.1000Ph.cambivoraPh.cinnamomi
Ph.ilicisPh.cactorum
Ph.capsiciHalophytophthora.batemanensis
P.viniferum.94P.violae.63
P.rhizosaccharum.78P.ramificatum.17P.middletonii.49
P.rostratum.56P.longisporangium.93P.bifurcatum.35
P.orthogonon.53P.nunn.51
P.campanulatum.04P.acanthophoron.52Pythium.sp.HS.66
P.ultimum.var.sporangiiferum.6P.splendens.42
P.glomeratum.39P.heterothallicum.62
P.undulatum.30Achlya.bisexualis
Pythiogeton sp. 2
Pythiogeton sp. 1
-.
Phylogenetic tree based in internal transcribed spacer ribosomal DNA region [ITS rDNA (ITS1, 5.8S, ITS2)] sequences constructed using Neighbour-joining analysis. Achlya bisexualis was used as outgroup.
Summary1. Three putative new species, Pythiogeton sp. 1,
2 and 3 were isolated from ornamental plant roots in North Carolina, USA.
2. The all species infected to roots of their host plants and radish, but had no visible symptom in an inoculation test performed in Petri dish.
3. The phylogenetic tree based in ITS rDNAshows that all Pythiogeton are a solid species and the closest are members that belong to Pythium (P. grandisporangium) than Phytophthora.