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

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Penetration and Establishment of Fungi in Seed 83pathogen to reach inside the ovary may be exclusive or follow a particular coursepredominantly together with other alternate courses. The former condition seems tooccur only rarely.4.3.1 ROUTES FOR INTERNAL OVARY INFECTIONThe infection may either reach the pistil directly from the mother plant through thevascular supply or the parenchyma, primarily through the intercellular spaces of thepedicel, or take place indirectly from outside using stigma-style, ovary or fruit wall,and other floral parts, including nectaries, as sites for the receipt of inoculum.Investigations carried out using artificial inoculation and histological techniques,including SEM, have improved our understanding of the course of hyphae duringpenetration and growth in the tissues of the pistil (Marsh and Payne, 1984; Chikuoand Sugimoto, 1989; Neergaard, 1989; Kobayashi et al., 1990).4.3.1.1 Direct Infection from Mother PlantSystemic plant infection of most vascular and nonvascular pathogens enters theflower and fruit through the pedicel (Figure 4.1A, B). Local infection below theflower, if it becomes systemic, can also cause infection via the pedicel (Lawrence,Nelson, and Ayers, 1981).4.3.1.1.1 Entry through Vascular SupplyVascular infection of wilt pathogens, Fusarium and Verticillium species, reaches thepistil via the vascular supply. Rudolph and Harrison (1945) isolated F. moniliforme,F. oxysporum, and F. scirpi from vascular bundles from all parts of the cotton plant,including boll and seed. Snyder and Wilhelm (1962) found that V. albo-atrum movedthrough the vascular elements of the mother plant into the flower and fruit stalk insugar beet and spinach. Verticillium dahliae also follow a similar mode of flowerand fruit infection in these crops (Van der Spek, 1972). Parnis and Sackston (1979)found mycelium of V. albo-atrum in vessels of the testa of Lupinus luteum seedsand believed that it spread through the funicular tissue. Infection via the vasculartissue (xylem) of the mother plant is the usual route for infection of garden stock(Mathiola incana) seed by F. oxysporum f. sp. mathiolae (Baker, 1948).Kingsland and Wernham ((1962) report that F. moniliforme invades the rudimentaryears in corn through vascular tissues of the stalk. But Lawrence, Nelson,and Ayers (1981) have found that sweet corn plants showing systemic or localinfection of F. moniliforme and F. oxysporum carry hyphae of the two fungi inintercellular spaces. The xylem vessels were found occluded in stem and leaves, butno hyphae were seen. The fungus moved through the parenchyma tissue of the stalkinto the cob and subsequently the pedicels of florets. Klisiewicz (1963) has observedmycelial tufts of F. oxysporum f. sp. carthami in infected receptacles of safflowerheads. Hyphae traversed through the abscission zone of the cypsil and were associatedwith them, but not limited to the xylem. Halfon-Meiri, Kunwar, and Sinclair(1987) have found colonization of achenes of Ranunculus asiaticus by Alternariafrom the mother plant through the vascular system.
84 Histopathology of Seed-Borne InfectionsstistypcchoovmyvemymfuvsBpdAFIGURE 4.1 (Color figure follows p. 146.) Direct infection of ovary and ovule from motherplant. A, Diagram showing direct movement of fungal infection (arrows) via vascular elements(xylem) and nonvascular tissues (parenchyma and intercellular spaces) in pedicel. Infectionmay pass through the placenta and funiculus into the ovule or after escaping from the placenta,it may pass through the funiculus and ovary wall into the locule (ovary cavity) and enter theovule via the micropyle and/or the surface of the ovule. B, Diagram of part of the pedicelregion to show the spread of infection via vascular and nonvascular tissues. (Abbreviations:ch, chalaza; fu, funiculus; m, micropyle; my, mycelium; o, ovary; ov, ovule; pc, parenchymacells; pd, pedicel; sti, stigma; sty, style; ve, vascular elements; vs, vascular supply.)4.3.1.1.2 Entry through Nonvascular TissuesIn plants systemically infected by smuts, downy mildew, and endophytes in cerealsand grasses, the mycelium moves through the intercellular spaces and enters the earfrom the mother plant. In smuts and downy mildews, this infection may lead tomalformation and disruption of reproductive structures (Mathre, 1978; Safeeulla,1976). In systemically infected plants of pearl millet by Sclerospora graminicola,finger millet by S. macrospora, and sorghum by Peronosclerospora sorghi, the
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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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Reproductive Structures and Seed Fo
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14 Histopathology of Seed-Borne Inf
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Page 47 and 48: 32 Histopathology of Seed-Borne Inf
Page 56 and 57: Reproductive Structures and Seed Fo
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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134 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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