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Identification of fungi detected on rice seed The standard detection method used in identifying fungi on rice seed at IRRI is given below. Figure 3 shows the parts of a rice seed attacked by fungi. With this method, numerous fungi have been detected on rice seed. The profile of each fungus detected is presented in the following pages. Methods and conditions of rice seed incubation for microorganism detection are listed below. The <strong>International</strong> Rules for Seed Testing recommend the blotter test for detecting seedborne fungi. The procedure involves these steps: 1. Prepare materials (9.5-cm plastic petri dish, marking pencil, round blotter paper, distilled water, sampling pan, forceps, seed sample). 2. Label plates accordingly using a marking pencil. 3. Place 2–3 pieces of moistened round blotter paper in labeled plastic petri dishes. 4. Sow 25 seeds per plate making sure that seeds are sown equidistantly with 15 seeds on the outer ring, 9 seeds at the inner ring, and 1 seed in the middle. 5. Incubate seeded plates at 21 °C under a 12-h light and 12-h dark cycle. Light sources can be near ultraviolet (NUV) light or daylight fluorescent tubes. The NUV light source can be a 320–400 nm lamp, preferably Philips TLD 36W/08 or GE F 40 BL. Daylight fluorescent tubes can be Philips TL 40W/54 day light or its equivalent. 6. Examine each of the seeds after 5–7 d of incubation for fungal growth. Partition between lemma and palea Lemma Awn Sterile lemmas Palea Fig. 3. Parts of a rice seed. 13
Seedborne fungi causing foliage diseases in rice Alternaria padwickii (Ganguly) Ellis syn. Trichoconis padwickii Ganguly Trichoconiella padwickii (Ganguly) Jain Disease caused: stackburn a. Symptoms On leaves—large oval or circular spots with a pale brown center and distinct dark brown margin. Color of center eventually becomes white and bears minute black dots. On grains—pale brown to whitish spots with black dots at the center and dark brown border. Roots and coleoptile of germinating seedlings— dark brown to black spots that eventually coalesce. Small, discrete, and black bodies are formed on the surface of the darkened area as decay proceeds. b. Occurrence/distribution Stackburn disease is widespread in most of the rice-growing countries worldwide (Fig. 4). c. Disease history The disease was first reported in the U.S. It resembles black rust of wheat on rice leaves, but only sclerotia and mycelium were observed. Later the fungus was observed in and on rice seeds. d. Importance in crop production Stackburn leaf spot disease is not considered to be of economic importance. However, seed infection results in grain discoloration, which may reduce germination and lower grain quality. The disease potential of stackburn is very low and the yield loss caused by A. padwickii in literature may be overestimated. The effect of infected seed on seed germination is not yet properly assessed. Detection on seed a. Incubation period on blotter A. padwickii is easily observed on seeds using the blotter method 5 d after seeding on moistened blotter and incubated under NUV at 21 °C. The detection frequency is about 67.1% on seeds coming from different regions (Fig. 5a,b). b. Habit character Seed infected with A. padwickii after incubation shows abundant aerial mycelia, hairy to cottony, profusely branched, grayish or hyaline when Fig. 4. Occurence of stackburn (Ou 1985, Agarwal and Mathur 1988, EPPO 1997). 14
Page 2 and 3: Contents Foreword Preface v vi INTR
Page 4 and 5: Introduction The purpose of seed he
Page 6 and 7: Functions of seed health testing Se
Page 8 and 9: % infected seed lots 100 80 60 40 2
Page 10 and 11: Table 3. Pathogen profiles closely
Page 12 and 13: Table 4. Germination (%) of untreat
Page 14 and 15: Microorganisms associated with seed
Page 18 and 19: Detection frequency (%) 100 80 60 4
Page 20 and 21: moderately fast and attain a 4.32-c
Page 22 and 23: Detection frequency (%) 120 100 Eas
Page 24 and 25: They are feathery to slightly fluff
Page 26 and 27: Observed frequency (%) 120 100 80 6
Page 28 and 29: Frequency level (%) 120 100 East As
Page 30 and 31: a 4.90-cm diam in 5 d. They are eve
Page 32 and 33: Detection frequency (%) 90 80 East
Page 34 and 35: gray, becoming dark near the margin
Page 38 and 39: Sarocladium oryzae (Sawada) W. Gams
Page 40 and 41: a b c e f d f Fig. 35. Habit charac
Page 42 and 43: Fig. 38. Occurrence of black kernel
Page 44 and 45: a b d → → → e → f → f →
Page 46 and 47: d a b e → → → → → f c g h
Page 48 and 49: Fig. 46. Occurrence of minute leaf
Page 50 and 51: of the agar plate appears slightly
Page 52 and 53: Detection frequency (%) 120 100 Eas
Page 54 and 55: Pinatubo oryzae Manandhar & Mew Dis
Page 56 and 57: ange with orange. The pionnotes are
Page 60 and 61: Other fungi detected on rice seeds
Page 62 and 63: a b e c d Fig. 65. Habit character
Page 64 and 65: a d d b c Fig. 69. Habit character
Page 66 and 67:
→ → → a b f f e d e e c f Fig
Page 68 and 69:
a b a Fig. 76. Habit character of F
Page 70 and 71:
a b d c d e e Fig. 79. Habit charac
Page 72 and 73:
a b c → → → d → Fig. 83. Ha
Page 74 and 75:
→ → → a b d c Fig. 86. Habit
Page 76 and 77:
a b c Fig. 89. Habit character of P
Page 78 and 79:
a b d c e Fig. 92. Habit character
Page 80 and 81:
→ → → → a b e f → c d Fig
Page 82 and 83:
a b c d Fig. 100. Habit character o
Page 84 and 85:
→ → → → → → a → →
Page 86:
Savary S, Willocquet L, Elazegui FA
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