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

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2Reproductive Structuresand Seed FormationSeed is the end product of sexual reproduction that takes place through sequentialchanges in the reproductive shoot, the flower in angiosperms. The ovules are bornein a closed structure, the ovary. The ovules and seeds may get infected at any stageduring their development either directly through the mother plant or through theinfected floral parts, including bracts and nectaries. The contacts between the plantand flower and in turn with the ovule and seed are important in understanding thecourse of such infections. The interface of pathogen and host may cause morphologicaland anatomical changes in tissues of the flower and may also affect thereproductive cycle, including seed formation. Green ear disease of pearl millet,caused by Sclerospora graminicola, results in the transformation of florets into leafystructures. Inflorescence or flower infection by Protomyces macrosporus in corianderand Albugo candida in Brassicaceae cause hypertrophy in the latter, and fruit gallformation in the former. Claviceps purpurea and other species, when infecting cerealflorets, cause the ovary to form fungal sclerotia instead of producing a kernel. Thecontents in the ovary are replaced by smut chlamydospores due to the infection ofSphacelotheca, Tilletia, Tolyposporium, and Ustilago in various cereal crops.The structure of flowers, the reproductive cycle, and seed formation are describedin this chapter. The aspects that may be relevant to pathogenesis are highlighted. Anoutline of the reproductive cycle is given in Figure 2.1.2.1 FLOWERThe flowers may occur singly (cotton, kenaf, cucumber, pumpkin, and melon) oraggregated in inflorescence — small (tomato, potato, and brinjal) to massive (rice,wheat, pearl millet, sunflower, and coriander). Stalked or sessile flowers are borneloosely (coriander, carrot, and tomato) or compactly (wheat, pearl millet, maize, andsunflower), have an orderly arrangement, and depending on the order of developmentof flowers, the inflorescence is classified into indeterminate (racemose) or determinate(cymose) type. In the former, the order of development of flowers is acropetal,with the youngest bud and flower near the growing tip (Brassica, Raphanus, andLinum), whereas in the latter, it is basipetal, with the growing point ending in aflower and subsequent ones produced in the axil(s) of bracts below the terminalflower (Lycopersicon, Sesamum, and Solanum). The presence of accessory structures,e.g., spathe in spadix (maize); involucre of bracts in capitulum (sunflower) andumbel (coriander and carrot); and glumes, palea, and lemma with florets in simple7
8 Histopathology of Seed-Borne InfectionsFLOWER (Reproductive shoot of angiosperms)Fertile AppendagesStamenantheranther sac(microsporangium)microspore mother cellsCallose depositionpachytene I onward,isolationTetrads of microspores(Tetrahedral andisobilateral mostly)MEIOSISCarpelovulenucellus(megasporangium)megasporemother cellTetrads of megaspore(Usually linear)Callose degradationUninucleate pollen grainsTwo mitolicdivisionsMale gametophyte(Pollen grains)3-celled with exine,and intine, autonomousphasePollination(Pollen on stigma, germination, pollen tube penetration)Pollen tubeStyleOvaryFunctional megasporeThree mitolicdivisionsFemale gametophytye(Embryo sac)(egg, 2 synergids,central cell, 3 antipodalcells)Through one of the synergidsOvuleEmbryo sacDOUBLE FERTILIZATIONsperm 1sperm 2eggcentral cellSyngamyTriple fusionChanges in ovule parts otherthan in embryo sac—Nucellus—Chalaza—Integument(s)Seed coatZygoteProembryoEmbryoPrimaryendosperm cellEndosperm(Absorbed orpersistent)True seeds(Ovary and/or other accessory structuresof flower forming protective covering)1-seeded indehiscent fruits(caryopsis, cypsil, achene, utricle, etc.)FIGURE 2.1 Schematic representation of reproductive cycle and seed formation, includingone-seeded indehiscent fruits in angiosperms.
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 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 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
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Structure of Seeds 57Endosperm: One
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Structure of Seeds 59scendembepsmuA
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Structure of Seeds 61Endosperm: Sca
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Structure of Seeds 63Chalaza simple
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Structure of Seeds 65stystypmerA Bc
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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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