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Pinatubo oryzae Manandhar & Mew
Disease caused: seed rot
a. Symptoms
Gray lesions on plumules.
b. Occurrence/distribution
Pinatubo oryzae is frequently encountered in rice
seed grown in the Philippines and other countries
occurring on both germinated and nongerminating
seeds (Fig. 56).
c. Disease history
This fungus was previously identified as Verticillium
cinnabarinum and re-identified as Pinatubo
oryzae in 1996. It has been detected from rice
seeds since 1982. It is highly probable that the
organism was already present earlier but there are
no literatures to document any efforts to identify
the fungus.
d. Importance in crop production
This fungus is a rice grain pathogen. It is minor in
importance to rice production.
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Detection on seed
a. Incubation period on blotter
Using the blotter test, P. oryzae can be observed
on rice seeds 5 d after incubation in NUV light at
21 °C. The detection frequency is about 25.2% on
rice seeds coming from different regions.
b. Habit character
Aerial mycelia are sparse to abundant and white
with loose and abundant branching. Conidia are
borne terminally and arranged in a flower-like
manner. Pionnotes present on the seed surface
are wet and creamy to pink or they hang under a
thin cover of aerial hyphae (Fig. 57 a-c).
c. Location on seed
P. oryzae is most often observed over the entire
seed surface (about 46%) (Fig. 58).
Microscopic character
a. Mycelia—hyaline, septate (Fig. 57d).
b. Conidiophore—simple or branched, short, septate
with denticles at the terminal portion (Fig. 57e).
c. Conidia—elongately oval, single- to 2-celled,
very rarely 3-celled; pointed at the basal portion
and rounded at the apical portion, hyaline (Fig.
57f). Measurements: 5.06–10.81 µ × 2.70–6.21 µ
(PDA); 5.75–12.88 µ × 2.76–5.98 µ (PSA); and
5.75–11.73 µ × 2.53–5.06 µ (MEA).
Colony characters on culture media (Fig. 59)
Colonies on PDA at ART (28–30 °C) grow relatively
fast and attain a 5.02-cm diam in 5 d. They are zonated
with even margins, floccose, and reddish or-
Fig. 56. Occurrence of Pinatubo oryzae on rice seed from different countries received at IRRI (IRRI-SHU unpublished
data 1990-97).
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