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