THE GENUS PYTHIUM - An-Najah National University

PYTHIUM INTERMEDIUM de Bary Bot. Ztg: 554 (1881). Figs 34-35
COLONY MORPHOLOGY:Colonies on CMA forming a radiate pattern.no
development of aerial mycehum. MYCELIUM: Main hyphae 3.5-7(av. 4.8»)lm
wide. SPORANGIA: Subglobose or spherical, 16-24(av. 19.4).um diam, mostly
terminal, occasionally intercalary, 2-8 in a. chain. Zoospores formed in water
culture in the presence of grass blade at 5-15C
SEXUAL STRUCTURES: Attempts to produce oogonia in dual cultures were
not successful; identification was based on vegetative structures.
TEMPERATURE _ GROWTH RELATIONSHIPS: Minimum 5°C, optimum
250C, maximum 300e. Daily growth rate on CMA at 25°C 21mm.
MATERIAL EXAMINED: ex Rosa sp, An-Najah University campus
(FCCAU 107.2);ex soil, Nablus (FCCAUI07.1), and Ram AlIa (FCCAUl07.3)
and several other isolates.
OCCURRENCE:Infrequently isolated from diseased roots, and rarely from
soil (found in 12% of the soils sampled). This species was also recorded from soil
in the Lebanon(Ahrens, 1971) and from fresh water in Egypt(El-Hissy, 1974).
PYTHIUM IRREGULARE Buisman,Meded. phytopath. Lab. Willie
Commelin Scholten 11:1-51(1927).
COLONY MORPHOLOGY:Colonies on CMA forming a diffuse pattern,
with a moderate amount of aerial mycelium. MYCELIUM:Main hyphae 3-7(av.
3.3) urn wide.SPORANGIA:Globose 13-35(av.25.3)jJm diam, terminal and
intercalary. Zoospores produced at 1O-15oe. OOGONIA:Globose to irregular,
intercalary and terminal, 15-23 (av. 18.5 ± 0.6-95% C.I.) urn diarn, smooth or
with a few blunt conical finger-like projections, up to 5/ oogonium.
ANTHERIDIA: 1-2(-3)/ oogonium, mostly monoclinous, usually stalked arising
at some distance from oogonium base, occasionally sessile or hypogynous;
antheridial stalks sometimes branched. OOSPORES:Aplerotic; IO-18(av. 15.0±
-95% C.l.j nm diam, wall 0.5-1.5 (av. 0.9 ± 0.1-95% C.I)..um thick. Ooplast 6-10
(av. 7.7).um diam. TEMPERATURE - GROWTH RELATIONSHIPS:
Minimum lOoC, optimum 30oC, maximum 3SoC. Daily growth rate on CMA at
250C l lmm.
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