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CHAPTER 17 Organisms causing grain discoloration and damage J.K. Misra, S.D. Merca, and T.W. Mew A number of weak parasites or saprophytes which have not yet been discussed in this manual in feet rice seeds at pre- and postharvest stages, causing syndromes referred to as grain discoloration. Grain discoloration may be on glumes, kernels, or both. The type and magnitude of discoloration vary with the place, environmental conditions, organisms involved, and several unknown factors. Not all organisms that cause grain discoloration have been studied or identified. Disease development Environmental factors such as continuous rain, humidity and temperature (27-35 °C) conducive to fungal and bacterial growth help increase thc incidence of grain discoloration. Strong winds, which cause plants to lodge against each other or to fall to the ground, contribute to grain discoloration. Grain discoloration may also occur during storage where poor aeration, high humidity, and high temperature prevail. Under conditions favoring luxuriant growth during storage, some species of Aspergillus, Fusarium, and Penicillium produce toxins as well as cause discoloration. Symptoms Symptoms may be one spot of any color (ranging from pale yellowish, brown, gray to black dots), lesions to bleached areas over glumes, or combinations of many discernible patches, lesions, or spots. Spots on the glumes or kernels affect both physical and chemical qualities of the grains. Table 17.1. Some fungi associated with discolored seeds. Species Sarocladium oryzae Curvularia spp. Trichoconiella padwickii Phoma spp. Fusarium moniliforme Fusarium sp. Verticillium cinnabarinum Nigrospora oryzae Fusarium semitectum Cochliobolus miyhabeanus Alternaria sp. Epicoccum purpurascens Penicillium sp. Fusarium sp. Cephalosporium sp. Sterile spp. Fusarium Penicillium spp. Aspergillus flavus Curvularia Frequency of detection (%) 46 41 36 21 10 8 7 6 5 23.4 13.4 4.9 4.9 1.2 1.2 19.7 40 25 22 60 Fungi and bacteria associated with discolored grains affect germinability (Misra et al 1990, Ou 1985). Table 17.1 lists some fungi which are associated with discolored seeds. Bacteria are found associated with 28-32% of discolored seed (Misra et al 1990, Baldacci and Corbetta 1964). Pseudomonas spp. (fluorescent and Reference Misra et al (1990) Baldacci and Picco (1948) Teunisson (1954) Rao and Salam (1954) Drechslera oryzae Alternaria padwickii Fusarium spp. Epicoccum sp. Alternaria sp. Drechslera oryzae Penicillium sp., Fusarium sp., Curvularia sp. and Pyricularia oryzae 9.1 7.9 14.6 30.2 19 9.2 2.6-0.42 Johnston (1958) Baldacci and Corbetta (1964)
nonfluorescent) and Erwinia herbicola are normally found associated with discolored seed. Nonfluorescent Pseudomonas strains cause discoloration and sterility in grains (Zeigler and Alvarez 1990). However, other bacteria present may cause this syndrome. More information is needed in this regard. Detection For details, see Chapters 6 and 7. Fungi. Blotter and/or agar plate methods detect most of the fungi. Some slow-growing fungi are better seen on a blotter. Somewhat different flora appear when seeds are plated on agar after surface sterilization with 1% sodium hypochlorite for 10 min. Control Fungicidal spray reduces the incidence of grain discoloration in the field. Weekly sprayings of benomyl (50% WP) at 1.0 kg formulation/ha, applied from early booting to early ripening stages, help reduce grain discoloration. Mancozeb (80% WP) is also effective (Bandong et al 1983). Postharvest operations to keep seeds clean, dry (13-14% moisture), and free from rodents and insects during storage can help prevent grain discoloration and consequent damage to seeds. 100 Rice seed health testing manual
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A Manual of Rice Seed Health Testin
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Contents Foreword v Preface vi Part
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Foreword Intensive collaboration ch
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Part 1 Introduction CHAPTER 1 Rice
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tional levels (Kahn 1988). Quaranti
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Morphology of the mature plant Matu
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two-celled, besifixed, deeply sagit
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Part 2 Procedures for seed health e
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CHAPTER 3 Equipment J.K. Misra, T.W
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3.2 Dry seed inspection using a mag
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Example. In a two-stage random samp
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solid pointed end. The tube and sle
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CHAPTER 5 Dry seed inspection J.K.
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Detection Blotter and agar plate me
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Results: Examine plates for charac-
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Extraction and isolation It is esse
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GRINDING METHOD (FOR SMALL-SCALE SE
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flagellum. Cells occur singly, in p
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7.6 Oxidase test reaction. L = colo
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7.9 Production of 2-ketogluconate.
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1. Grow pathogen-free plants under
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7.12 a. P. glumae type A colony on
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A1. Macerate 100 seeds in 10 ml of
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Results: 7.Streak the bacteria onto
Page 55 and 56: Sieve method (Fig. 8.1) Procedure:
Page 58 and 59: CHAPTER 10 Field inspection J.K. Mi
Page 60 and 61: Table 10.2. continued Disease Fungi
Page 62 and 63: Table 10.2. continued Disease Growt
Page 64: additional precaution, the multipli
Page 67 and 68: terracoat (5-ethoxy-3- trichloromet
Page 70: Part 3 Pests and pathogens CHAPTER
Page 73 and 74: elevant tests for determining the i
Page 75 and 76: Table 12.1 continued Family and spe
Page 77 and 78: Cryptolestes pusillus Schonherr The
Page 79 and 80: Rice weeviI Scientific name: Sitoph
Page 82 and 83: CHAPTER 14 Fungal pathogens J.K. Mi
Page 84 and 85: THE DISEASE—BROWN SPOT Sir John W
Page 86 and 87: Symptoms Glumes are discolored, and
Page 88 and 89: y low relative humidity. Released a
Page 90 and 91: THE DISEASE—STEM ROT Stem rot was
Page 92 and 93: THE DISEASE—SHEATH BLIGHT Sheath
Page 94 and 95: Sarocladium oryzae is seedborne. Th
Page 96: Although not currently considered a
Page 99 and 100: Pseudomonas fuscovaginae Pathogen:
Page 101 and 102: See Chapter 7 and Figure 15.4a for
Page 103 and 104: Infected seeds and contaminated wat
Page 105: For further details, see the Common
Page 109 and 110: Franklin M T, Siddiqi M R (1972) Ap
Page 111 and 112: Tai F L, Siang W N (1948) 'I-chu-hs
Page 113 and 114: 106 Rice seed health testing manual
Page 115 and 116: 108 Rice seed health testing manual
Page 117 and 118: After autoclaving the medium, add t
Page 119 and 120: smoniloid = having swellings at reg
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