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Reproductive Structures and Seed Formation 19iifumoinuesintarvsAchBCmgmDEFsynecpnusnuantGHIJFIGURE 2.7 Structure of ovule and development of female gametophyte. A, Ls bitegmic andcrassinucellar ovule. B to J, Sesamum indicum. B, Ls unitegmic and tenuinucellar ovule. C, Lsovular primordium with female archesporium. D to F, Ls parts of ovules with megaspore mothercell, dyad with dividing nuclei and triad with nucleus of the micropylar dyad cell in dividingstage. G to J, Two-, four-, and eight-nucleate, and organized embryo sacs. (Abbreviations: ant,antipodal cells; ar, archesporium; ch, chalaza; ec, egg cell; es, embryo sac; fu, funiculus; ii,inner integument; int, integument; m, micropyle; mgm, megaspore mother cell; nu, nucellus;oi, outer integument; pnu, polar nuclei; snu, secondary nucleus; syn, synergid; vs, vascularsupply.) (B to J, From Singh, S.P. 1960. Phytomorphology 10: 65–82.)
20 Histopathology of Seed-Borne Infectionslong funicle almost completely surrounds it, the ovule is called the circinotropoustype.The ovules are also classified as crassinucellar and tenuinucellar. In the former,parietal layers exist between the nucellar epidermis and the female gametophyte(Figure 2.7A), whereas in the latter the nucellar epidermis alone covers the femalegametophyte (Figure 2.7B, E). The tenuinucellar ovules are characteristic of sympetalae(Lycopersicon, Solanum, Sesamum, Helianthus, and Lactuca) while otherdicotyledons (Gossypium, Hibiscus, Glycine, Vigna, Phaseolus, Pisum, Cucurbita,and Cucumis) and monocotyledons (Triticum, Hordeum, Zea, Oryza, and Allium)have crassinucellar ovules.The ovules have one (Figure 2.7B) or two integuments (Figure 2.7A). In bitegmicovules, the inner integument is largely of dermal origin except in Euphorbiaceae(Bor and Bouman, 1974) and Malvaceae (Joshi, Wadhwani, and Johri, 1967; Kumarand Singh, 1990), but the outer integument or the single integument is of subdermalor dermal origin. The integument arises as a rimlike outgrowth and grows to enclosethe nucellus to various extents, having an opening at the apex, the micropyle. Themicropyle may be formed by both the integuments or by the outer or inner integumentalone. Electron microscopy has shown that the micropyle in Beta vulgaris containsa fibrillar periodic acid-Schiff positive substance and is often covered by a thin sheetor hymen (Olesen and Bruun, 1990).2.5.2 VASCULAR SUPPLY OF OVULEThe ovule in angiosperms commonly receives a single vascular bundle from theventral carpellary vein (Figure 2.6A), rarely two or more in Sechium and Sicyos(Puri, 1954; Singh, 1965). The vascular supply ends as such or after fanning out inthe chalaza (Figure 2.6B, C). The ovular supply may extend in the outer (Cucurbitaceaeand Fabaceae) (Figure 2.6D, E) or the single integument (Asteraceae andConvolvulaceae) on antiraphe side and rarely in the inner integument as in Euphorbiaceae(Figure 2.6F, G). Integumentary vascularization is rare in monocotyledons.Large ovules usually have a developed vascular supply, whereas small ones showreductions. Very small ovules as in Orchidaceae have no trace of vascular supply.The integumentary vascular supply may be unbranched, or branched in some cases,forming a network of bundles (Kuhn, 1928). Vascular elements, xylem and phloem,may become differentiated in later developmental stages, or it may not take place,and the vascular supply consists of procambial strands only.Nucellar tracheids are known in the Asclepiadaceae, Capparidaceae, Casuarinaceae,Amantiferae, Liliaceae, and Olacaceae. The tracheids are annular or spiral,very small, slender, and usually isolated or in small clusters.2.5.3 CUTICLES IN OVULECuticles are reported to be present in ovules from early stages of development. Theovule primordium bears a cuticle. After the development of the integuments in abitegmic and crassinucellar ovule, as many as five cuticular layers may be identified:(1) on the outside of the outer integument and the funiculus; (2) on the inside of the
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 33: 18 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
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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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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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