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

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Structure of Seeds 51is found in association with seed coats with pores, whereas the closed type is foundwith those without pores. Kulik and Yaklich (1991) found that hyphae of Phomopsisphaseoli were present on the seed coat and hilum, and their penetration via the opentype of micropyle was far more prevalent than in seeds of cultivars with closedmicropyles.3.2.6 HILUMThe size, shape, and position of the hilum with respect to the micropyle and chalazaconstitute important features. The hilum is generally considered to be a scar leftafter separation of the seed from the funiculus. Recent studies have shown that itevolves during seed development. Partial seed abscission is observed during hilumdevelopment (Pamplin, 1963; Baker and Mebrahtu, 1990). The scar is not the resultof mechanical separation, but rather caused by the organization of an abscissionlayer. Hilum size varies from insignificant to quite prominent. In the latter, the cellorganization in the hilar region may differ from that of the seed coat. The cells maybe homogeneous or show tissue differentiation, as in fabaceous seed (Baker andMebrahtu, 1990). The broad surface of hilum lacks the usual cuticle and may havefissures. Hilar fissure is characteristic in the seeds of Fabaceae.3.2.7 RAPHEIn several types of ovules and seeds, the funiculus is adnate to the ovule surface.The abscission of seed occurs in the free part of the funiculus. The adnate partremains as a longitudinal ridge in seed and is called the raphe. Structurally, it usuallyresembles the seed coat, but sometimes it is distinctive.3.2.8 SEED APPENDAGESSeeds have various types of appendages, such as aril (Figure 3.2E, F), caruncle(Figure 3.2C, D), strophiole, wings (Figure 3.2A, B), and hairs. The aril is a soft,succulent local outgrowth of seeds of varied origin. The aril primordium may developfrom any part of the ovule (e.g., funicle, raphe, and chalaza), the placenta, or thecarpel. It may enclose the seed more or less completely as in Passiflora (Figure3.2F) or it may form a localized outgrowth in Turnera ulmifolia (Figure 3.2E) andothers. For detailed information on seed appendages in general and aril in particular,the reader should refer to Kapil, Bor, and Bouman (1980).Caruncle (Figure 3.2C, D) is a small, disclike appendage, the attachment andgrowth of which are limited to the exostome rim. The micropyle may be seen in thecenter (Ricinus and Euphorbia). Strophioles are glandular or spongy, with proliferationlimited only to the raphal region (Chelidonium majus).Wings (Figure 3.2A, B) are flattened extensions of seed having optimal strengthand a minimal biomass. Seed wings are often correlated with seed dispersal. Corner(1976) believes that the seed wings are local outgrowths of the testa. They may beperipheral or restricted to the raphe, chalaza, antiraphe, hilum, or funicle. Seed wingsare rarely provided with vascular bundles, whereas fruit wings have a well-developedvascular supply.
52 Histopathology of Seed-Borne InfectionsABCDEFFIGURE 3.2 SEM photomicrographs of seed appendages. A, B, Winged seed of Nemesiafloribunda, circular wing having reticulate patterns of elongated cells. C, D, Lobed caruncleof Euphorbia lathyris. E, Unilateral raphal aril of Turnera ulmifolia. F, Funicular aril coveringthe seed on all sides of Passiflora suberosa. (From Kapil, R.N., Bor, J., and Bouman, F. 1980.Bot. Jahrb. Syst. 101: 555–573. With permission.)Seed hairs are common in many families, particularly Malvaceae, Cochlospermaceae,Asclepiadaceae, Convolvulaceae, Acanthaceae, and Polygalaceae. Usually theseed hairs are simple and unicellular with a thin or thick cuticle; however, multicellularhairs are known in some Rutaceae. The hairy structures on the seed surface in
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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 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
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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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102 Histopathology of Seed-Borne In
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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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