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Reproductive Structures and Seed Formation 312.8.4 CHANGES IN CHALAZAThe chalaza may or may not undergo significant changes in seed. In the formercondition it is punctiform or unspecialized. However, in Euphorbiaceae, Asteraceae,Meliaceae, Annonaceae, and Myristicaceae, the chalaza undergoes general amplificationcontributing a significant portion of the mature seed. Such seeds are calledpachychalazal (Periasamy, 1962). If the growth in chalaza is localized, forming aband or hoop around the nucellus, the chalaza is called the perichalaza (Corner,1976).The chalazal tissue may undergo differentiation similar to that taking place inthe integuments (outer or single one), or it may have independent changes. In mostseeds the epidermis in this region becomes thick walled and lignified.2.8.5 CHANGES IN INTEGUMENTSThe ovules are bi- or unitegmic. In a bitegmic ovule, both integuments form theseed coat in Brassicaceae (Rathore and Singh, 1968; Prasad, 1974; Harris, 1991),Malvaceae (Joshi, Wadhwani, and Johri, 1967; Kumar and Singh, 1990), Euphorbiaceae(Singh, 1954), Amaranthaceae, Chenopdiaceae (Taneja, 1981), Linaceae(Boesewinkel, 1980), and Liliaceae (Sulbha, 1954), whereas in many families theinner integument degenerates and the outer integument alone forms the seed coat,e.g., Fabaceae (Corner, 1976; Pandey and Jha, 1988) and Cucurbitaceae (Singh,1953; Singh and Dathan, 1972, 1990). In Poaceae, it is the inner integument thatforms the seed coat, the outer one degenerates (Bradbury, Cull, and MacMarters,1956; Bradbury, MacMasters, and Cull, 1956; Naryanaswami, 1953; Chandra, 1963,1976). Seeds in some of the Poaceae are without a seed coat.The cells of the integuments divide anticlinally to keep pace with the growingseed. This is also attained through the enlargement of cells. The integuments mayor may not undergo periclinal divisions, and they are called multiplicative andnonmultiplicative, respectively. Both outer and inner integuments are nonmultiplicativein Amaranthaceae, Chenopodiaceae, and Liliaceae; the outer integument ismultiplicative in Fabaceae and Cucurbitaceae; and the inner integument is multiplicativein Malvaceae, Euphorbiaceae, and Linaceae. Multiplication in cell layers maybe diffuse, spread all over, or be localized, confined to certain zones. The moststriking example of localized multiplication is Cucurbitaceae (Singh, 1953; Singhand Dathan, 1972, 1990) in which the outer epidermis of the outer integument andits derivatives undergo periclinal divisions (Figure 2.15B, G).During development the integument undergoes differentiation, absorption of celllayers, and thickening of cell walls. In some cases, the deposition of pigmentedmaterial, mucilage, tannin, and crystals takes place. One or more layers of seed coatdevelop characteristic thickenings, forming the main mechanical tissue. The placeof origin in the integument and the structure of cells of the main mechanical layerare characteristic in the seeds of a family. Depending on whether the main mechanicallayer differentiates in the outer or inner integument, Corner (1976) has classifieddicotyledonous seeds formed from bitegmic ovules into testal or tegmic types. Eachof these types is further subdivided into exotestal, mesotestal, and endotestal, and
32 Histopathology of Seed-Borne Infectionsexotegmic, mesotegmic, and endotegmic on the basis of the position of the mainmechanical layer in the outer epidermis, middle layers, or inner epidermis of theouter or the inner integument, respectively.2.9 SEED COAT DEVELOPMENT IN SELECTED GENERAThe seed coat development for some economically important plants, e.g., for trueseeds of Brassica (Brassicaceae), Hibiscus, Gossypium (Malvaceae), Crotalaria(Fabaceae), Lycopersicon (Solanaceae), Cucurbita, Sechium (Cucurbitaceae), andone-seeded indehiscent fruits of Lactuca (Asteraceae) and Triticum (Poaceae), isdescribed.2.9.1 BRASSICAThe ovule is bitegmic; initially each integument is two or three-layered. Both theinteguments show slight multiplication. The outer integument becomes four-layered(Figure 2.13A). The cells in the inner epidermis of the outer integument elongateradially, and those of the other layers stretch tangentially and lose contents. Thecells of the inner epidermis acquire U-shaped thickenings, forming the main mechanicallayer in the mature seed coat (Figure 2.13C, D).The inner integument becomes many-layered (Figure 2.13B), and its cellsenlarge and undergo absorption during seed development (Figure 2.13C). The innerepidermis persists and forms the endothelium. Its cells develop pigmented materialand some proteinaceous bodies (Vaughan, 1956, 1959; Rathore and Singh, 1968;Prasad, 1974). The mature seed coat consists of layers of the outer integument andthe endothelium (Figure 2.13D).2.9.2 CROTALARIAThe ovules are bitegmic (Figure 2.13E, F) but the inner integument disappears duringdevelopment (Figure 2.13G, H) and the outer integument alone forms the seed coat.The outer integument is multiplicative. The cells of the outer epidermis elongateradially and form the palisade layer of sclereids or macrosclereids (Figure 2.13G toI). This is the main mechanical layer in fabaceous seed.The cells of the subepidermal layer become columnar, develop unequal thickenings,and form the hourglass cells (Figure 2.13H). The remaining layers remainthin-walled and stretch tangentially, and are partly digested during development(Corner, 1976; Pandey and Jha, 1988).The differentiation in the hilar region in developing fabaceous seed and itsstructure at maturity are quite characteristic (Baker and Mebrahtu, 1990), The regionconsists of rim-aril (when present), counter palisade (differentiated in the funiculus),hilar fissure, palisade layer (macrosclereids), tracheid bar, stellate parenchyma, andaerenchyma (Figure 2.13I). The development of hilar fissure, counter palisade,tracheid bar, and stellate parenchyma begins quite early and is nearly completed bythe time 35% maximum seed size is attained in soybean (Baker and Mebrahtu, 1990).
Page 2 and 3: Histopathology ofSeed-Borne Infecti
Page 4: PrefaceThe book deals with only one
Page 8 and 9: The AuthorsDalbir Singh, Ph.D., for
Page 10 and 11: ContentsChapter 1 Introduction ....
Page 12 and 13: 4.3.2 Routes for Infection from Ova
Page 14: 8.4 Survival in Seed ..............
Page 17 and 18: 2 Histopathology of Seed-Borne Infe
Page 19 and 20: 4 Histopathology of Seed-Borne Infe
Page 22 and 23: 2Reproductive Structuresand Seed Fo
Page 24 and 25: Reproductive Structures and Seed Fo
Page 26: Reproductive Structures and Seed Fo
Page 29 and 30: 14 Histopathology of Seed-Borne Inf
Page 45: 30 Histopathology of Seed-Borne Inf
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
Page 68 and 69: Structure of Seeds 53dry seed of Ly
Page 70 and 71: Structure of Seeds 553.3.2 SEED COA
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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82 Histopathology of Seed-Borne Inf
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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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