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

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Structure of Seeds 53dry seed of Lycopersicon and some Solanum species are not true hairs. Saxena (1970)has shown that these are the radial walls of seed epidermal cells with thickeningdecreasing from inside to outside. These have been termed spurious hairs by Corner(1976) and pseudohairs by Rick (1978).Seed appendages do not occur universally and they are rare in crop plants. Theycause an increase in seed surface and this may promote association of microorganisms;however, no data exist to support this fact.3.3 INTERNAL MORPHOLOGY3.3.1 GROSS INTERNAL MORPHOLOGYThe gross internal morphological features of the main components of seed, i.e., theseed coat, endosperm and perisperm, and embryo, give an idea of their spatial andtopographic adjustments. The usefulness of these features as taxonomic pointers iswidely recognized (Bouman, 1974). These features are also significant in the functionalperformance of seed.Martin (1946) described the comparative morphology of seeds of 1287 generaof angiosperms and proposed a classification of seed types on the basis of the sizeof the embryo in relation to the endosperm, and on the differences in size, shape,and position of the embryo (Figure 3.3). He used embryo measurements in quarterunits of a circle and designated five types: (1) small, with the embryo smaller thana quarter of internal space; (2) quarter, with a quarter or more but less than twoquarters internal space; (3) half, with two quarters or more but less than three quartersinternal space; (4) dominant, with more than three quarters internal space; and (5)total, with the embryo occupying the entire inner seed space.On the basis of embryo position, Martin (1946) proposed three main categoriesof seed: basal, peripheral, and axile. Because of their overlapping features the basaland peripheral categories are merged into a single category called the peripheral.These categories are further subdivided on the basis of size and shape of the embryo.The peripheral type with the embryo at the micropylar end or oriented peripherallyand with copious endosperm or perisperm has five subcategories: (1) rudimentary,where the embryo is small, globular to ovate oblong, and relatively undifferentiated(Magnolia and Piper); (2) broad, where the embryo is as wide as or wider thanlong, globular, or lenticular (Nymphaea and Juncus); (3) capitate, where theembryo is distally expanded (Dioscorea, Tradescantia, Scirpus, and Carex); and(4) lateral, where the embryo is lateral, inclined to expand along the periphery(Poaceae); and (5) peripheral, where the embryo is elongated, large, often curved,extending along the periphery, with cotyledons narrow or expanded (Amaranthaceae,Chenopodiaceae).The axile type has small to large embryo, straight, variously curved or coiled,central, seeds small to large, and endospermic or nonendospermic. It has sevensubtypes: (1) linear, where the embryo is much longer than broad, with the cotyledonsstraight, curved, or coiled (Lilium and Allium); (2 and 3) dwarf and micro,where the seeds are small, with the seed interior 0.2 to 0.3 mm long in (2) and lessthan 0.2 mm long in (3), the embryo is small or large (Orchidaceae, Burmanniaceae,
54 Histopathology of Seed-Borne InfectionsSize designations for embryosmallquarterhalfdominanttotalSeed types based on position, size and shape of embryoPeripheralrudimentarybroadcapitatelateralperipheralAxilelineardwarfmicrospatulatebentfoldedinvestingFIGURE 3.3 Types of seed according to Martin (1946). The size designations refer to theembryo–endosperm size ratio, represented volumetrically in quarter units of a circle. The twomain groups, peripheral and axile seeds, are characterized based on the size, shape, andposition of embryo in seed. (Adapted and redrawn from Martin, A.C. 1946. Am. Midl. Nat.36: 513–660.)and Orobanchaceae); (4) spatulate, where the embryo is erect, the hypocotyledonaryaxis is not enclosed by cotyledons or only slightly enclosed (Corchorus, Sesamum,and Linum); (5) bent, where the embryo is bent like a sac knife, and the cotyledonsare expanded (Moraceae); (6) folded, the embryo is curved with folded cotyledons(Gossypium, Hibiscus, Brassica, Eruca, and Ipomoea); and (7) investing, where theembryo is erect and the cotyledons are large and enclose the hypocotyl axis (Cucurbitaceaeand Mimosoideae).Martin and Barkley (1961) used the above features in their Seed IdentificationManual.
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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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Page 22 and 23: 2Reproductive Structuresand Seed Fo
Page 24 and 25: Reproductive Structures and Seed Fo
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Page 62 and 63: 3Structure of SeedsThe seed habit i
Page 64 and 65: Structure of Seeds 49(1971) of usin
Page 66 and 67: Structure of Seeds 51is found in as
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Page 72 and 73: Structure of Seeds 57Endosperm: One
Page 74 and 75: Structure of Seeds 59scendembepsmuA
Page 76 and 77: Structure of Seeds 61Endosperm: Sca
Page 78 and 79: Structure of Seeds 63Chalaza simple
Page 80 and 81: Structure of Seeds 65stystypmerA Bc
Page 82 and 83: Structure of Seeds 67epsent endCADB
Page 84 and 85: Structure of Seeds 69perhscendembpe
Page 86 and 87: Structure of Seeds 71eposgepi′epo
Page 88 and 89: Structure of Seeds 73(Zea and Sorgh
Page 90 and 91: Structure of Seeds 75Baker, D.M. an
Page 92 and 93: Structure of Seeds 77Maheshwari Dev
Page 94: Structure of Seeds 79Vries, M.A. de
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TABLE 5.6Location of Mycelium of St
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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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