Histopathology of Seed-Borne Infections - Applied Research Center ...

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Location of Fungal Hyphae in Seeds 135A B CDEFG H IFIGURE 5.15 Photomicrographs of parts of seeds infected by Drechslera and Bipolarisspecies. A to G, D. graminea in barley kernels. A, B, Cleared whole-mounts of persistentlodicules showing hyphae. C to F, Whole-mounts of husk, aleurone layer, endosperm, andscutellum, respectively, having abundant hyphae. G, Ls part of embryo showing base of thecoleoptile having hyphal bits (arrow). H, I, Ls part of pericarp and endosperm in wheat kernelsshowing inter- and intracellular hyphae (arrows) of B. sorokiniana. (A to G, From Thakkar,R. 1988. Ph.D. thesis, University of Rajasthan, Jaipur, India; H, I, From Yadav, V. 1984. Ph.D.thesis, University of Rajasthan, Jaipur, India.)
136 Histopathology of Seed-Borne InfectionsInfected embryos remain thin, and those with heavy infection possess mycelium inall parts. Occasionally, embryos develop induced premature xylogenesis in themesocotyl and lysogenous cavities (Yadav, 1984). More deleterious effects on wheatembryo are caused by Drechslera tetramera than by B. sorokiniana.The inter- and intracellular mycelium of Bipolaris maydis occurs in the basalcap, closing tissue, and pericarp in weakly infected maize kernels, but it is abundantin the pericarp, basal cap, closing tissue, aleurone layer, endosperm, and embryo inheavily infected seeds (Singh, Singh, and Singh, 1986a).Drechslera graminea, which causes leaf stripe disease in barley, is seed-borne.According to Vogt (1923), Genau (1928), and Platenkamp (1975), the hyphae areconfined to the pericarp. Thakkar et al. (1991) found that moderate to heavily infectedseeds are symptomatic, and the expanse of mycelium and its effect on embryo arevariable. In moderately infected seeds, the hyphae may be confined to the pericarp(husk) and vascular strand of seed, or they may invade persistent lodicules (Figure5.15A, B), all layers up to the aleurone layer (Figure 5.15C, D), or penetrate theendosperm and rarely the embryo (Figure 5.15E to G). The hyphae spread interandintracellularly in all parts of heavily infected kernels. In very heavily infectedseeds, hyphae freely traverse from one part to another, binding the tissues and makingit difficult to separate husk, pericarp, aleurone layer, and even endosperm. Heavilyinfected seeds may have a small well-formed embryo, a shriveled poorly differentiatedembryo, or undifferentiated embryonal mass. The mycelium invades all partsexcept seminal leaves and the plumule bud in small embryos, all parts of shriveledembryos, and formless embryos. Barley kernels with deep infection of D. gramineafail to germinate (Thakkar, 1988).Bipolaris oryzae, a serious pathogen that causes brown leaf spot in rice, occursin the pericarp, seed coat, and endosperm (Fazli and Schroeder, 1966). Paul (1987)noted B. oryzae in the husk (palea and lemma), pericarp on the embryal side, andhilar region in weakly infected kernels. It spread all over the pericarp and testa, butnot in the endosperm and embryo in moderately infected seeds. In shriveled heavilyinfected seeds, B. oryzae occurred in all parts. The fungus formed pseudosclerotiabetween pericarp and testa and between testa and aleurone layer. Hyphae occurredin the peripheral layers of the endosperm and in the scutellum and other tissues ofthe embryo.5.5.4.1.4 CylindrocladiumCylindrocladium black rot caused by Cylindrocladium crotalariae is widespread inpeanut-growing areas in the United States. Porter et al. (1991) found a high degreeof correlation between the incidence of disease in the field and seed infection.Hyphae of C. crotalariae ramified both inter- and intracellularly in cells of the seedcoat in discolored seeds. Seeds with dark brown seed coat carried hyphae in cotyledonsalso. In these seeds, abundant hyphae occurred in the seed coat, between theseed coat and the cotyledons, and in cells of cotyledons (Porter et al., 1991). Porteret al. (1991) have proposed cleaning seed lots by removing shriveled and discoloredseeds to check the disease transmission.
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Histopathology ofSeed-Borne Infecti
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PrefaceThe book deals with only one
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The AuthorsDalbir Singh, Ph.D., for
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ContentsChapter 1 Introduction ....
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4.3.2 Routes for Infection from Ova
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8.4 Survival in Seed ..............
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2 Histopathology of Seed-Borne Infe
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4 Histopathology of Seed-Borne Infe
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2Reproductive Structuresand Seed Fo
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Reproductive Structures and Seed Fo
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14 Histopathology of Seed-Borne Inf
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3Structure of SeedsThe seed habit i
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Structure of Seeds 49(1971) of usin
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Structure of Seeds 51is found in as
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Structure of Seeds 53dry seed of Ly
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Structure of Seeds 553.3.2 SEED COA
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Structure of Seeds 57Endosperm: One
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Structure of Seeds 59scendembepsmuA
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Structure of Seeds 61Endosperm: Sca
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Structure of Seeds 63Chalaza simple
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Structure of Seeds 65stystypmerA Bc
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Structure of Seeds 67epsent endCADB
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Structure of Seeds 69perhscendembpe
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Structure of Seeds 71eposgepi′epo
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Structure of Seeds 73(Zea and Sorgh
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Structure of Seeds 75Baker, D.M. an
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Structure of Seeds 77Maheshwari Dev
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Structure of Seeds 79Vries, M.A. de
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186 Histopathology of Seed-Borne In
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7Seed Infection by VirusesViruses a
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Seed Infection by Viruses 201TABLE
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Seed Infection by Viruses 205Unlike
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Seed Infection by Viruses 2073. The
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Seed Infection by Viruses 209Wilcox
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Seed Infection by Viruses 213floret
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Seed Infection by Viruses 215ptowvv
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Seed Infection by Viruses 2177.4.2
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Seed Infection by Viruses 219seed(s
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Seed Infection by Viruses 221AMV fo
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Seed Infection by Viruses 223REFERE
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Seed Infection by Viruses 225Hunter
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Seed Infection by Viruses 227Wolf,
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