Untitled - International Rice Research Institute

Frequency level (%)
120
100
East Asia
Europe
Latin America
South Asia
Southeast Asia
Sub-Saharan Africa
80
60
40
20
0
Detection level (%)
50
40
30
20
10
0
1990 1991 1992 1993 1994 1995 1996 1997
Year
Fig. 19. Detection frequency (a) and level (b) of Microdochium oryzae from imported untreated seeds, 1990-97.
(pionnotes) varying in size and thickness are scattered
on seed surface (Fig. 20a-c).
c. Location on seed
M. oryzae is most likely observed growing on
sterile lemmas of the rice seed (about 55%) (Fig.
21).
Microscopic character
Conidia (epispore)—borne on superficial stromata
arising on lesions, bow-shaped; single-celled when
young, 2-celled when mature; one septum; occasionally
2–3 septate; not considered at septum; thinwalled,
hyaline, pink in mass, hyaline under the microscope
(Fig. 22d). Measurements: 8.97–17.48 µ ×
2.53–5.98 µ (PDA); 8.51–18.17 µ × 6.21–8.51 µ
(PSA); and 10.36–15.64 µ × 2.30–5.52 µ (MEA).
Colony characters on culture media (Fig. 22)
Colonies on PDA at ART (28–30 °C) grow moderately
fast, thinly spreading, and attain a 4.20-cm diam
in 5 d. They are evenly zonated with uneven margins,
orange with scanty, white aerial mycelia, and
somewhat pressed to the media. Colonies appear wet
at the center, spreading outward with age. The
colony on the reverse side of the agar plate appears
evenly zonated and light orange. At 21 °C under alternating
12-h NUV light and 12-h darkness, colonies
are thinly spreading, grow moderately fast, and attain
25