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

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Reproductive Structures and Seed Formation 9or compound spikes (wheat, barley, pearl millet, and rice), provide additional protectionto flowers, but cause increased humidity around them. They may also providea conducive environment for the development of pathogens that succeed in invadingthem.The flower is a shoot of determinate growth. The distal end of the axis is swollenor cup-shaped, forming a thalamus or receptacle, which bears laterally floral organs.A typical flower of dicotyledons has four types of organs comprising two whorls ofsterile appendages, the sepals and petals collectively called the calyx and corolla,respectively, and two whorls of fertile appendages, the stamens and carpels, collectivelytermed the androecium and gynoecium. The appendages are arranged on thereceptacle in succession spirally or in whorls. Many variations occur in size, shape,color, and number of members in each whorl and in their organization. Usually inmonocotyledons, there is only one whorl of sterile appendages, termed the perianth(onion and garlic). Flowers may be bisexual or unisexual. In the unisexual conditionstaminate and pistillate flowers are monoecious, or borne on one plant, as in maize,cucumber, pumpkin, and squash. If the staminate and pistillate flowers occur ondifferent plants, as in papaya, they are dioecious.In a flower, if the floral appendages are inserted successively one above the otherbelow the gynoecium (carpel), the flower is hypogynous and the ovary is superior(Figure 2.2A). When the receptacle becomes concave and surrounds the ovary or isfused with the ovary wall so that the sepals, petals, and stamens arise from the topof the ovary (Figure 2.2B), the flower is epigynous and the ovary is inferior as incoriander, cumin, carrot, cucumber, pumpkin, squash, sunflower, lettuce, apple, andpear. In an epigynous flower, the ovary is exposed to the environment from initiationuntil maturity, i.e., the formation of fruit.The flower in the grass family, Poaceae, is subsessile and bracteate; the drychaffy lemma, which is usually awned, is the bract. The dry membranous structureon the posterior side is known as the palea, which represents two fused posterolaterallysituated bracteoles. The palea encloses the flower and itself is enclosed by thelemma. The flower consists of lodicules (tepals), androecium, and gynoecium. Usuallythere are two fleshy, often hairy, lodicules situated in the anterolateral position.In Bambusa, there are six lodicules. Above the lodicules, there are usually threestamens and rarely more, six or less in Oryza and Bambusa, etc., two in Anthraxon,and one in Uniola. The gynoecium is tricarpellary and syncarpous and the ovary isunilocular with a single large ovule. The vascular anatomy has shown that theplacentation is parietal and that two of the three placentae are sterile. The ovarybears two laterally situated feathery styles and stigma.2.1.1 VASCULARIZATION OF FLOWERThe anatomical structures of the peduncle (axis of the inflorescence) and the pedicelare similar to that of the stem. The vascular cylinder may be continuous or split.The vascular bundles of the pedicel at a higher level break up and give out tracesto the floral appendages in succession in a hypogynous flower (Figure 2.2A). Thevascular traces meant for the floral appendages enter each unit either unbranched orafter undergoing further branching. Each sepal generally receives three traces, a
10 Histopathology of Seed-Borne InfectionsstistyoovdctvsvctspespeseoseABFIGURE 2.2 Structure and vascularization of angiospermous flower. A, Longitudinal section(Ls) showing vascular supply in hypogynous flower, traces of each whorl separate in thethalamus and diverge at corresponding places. B, Ls epigynous flower, traces for carpels arethe first to diverge while those of calyx, corolla, and androecium diverge at levels above theovary. (Abbreviations: dct, dorsal carpellary trace; o, ovary; ov, ovule; pe, petal; s, stamen;se, sepal; sti, stigma; sty, style; vct, ventral carpellary trace; vs, vascular supply.)petal with a single median trace or a median trace with two or more laterals, andthe stamen a single trace. The carpel is vascularized with a median (dorsal) and twolateral (ventral or marginal) traces. The ventral traces unite partially or completelyinto a single ventral trace. The ventral trace(s) are generally limited to the ovulebearingpart of the carpel. The vasculature in an epigynous flower differs only inthe manner of resolution or departure of vascular traces from the main cylinder. Thevascular traces of the whorls of appendages depart at levels higher than that of thegynoecium (Figure 2.2B). Thus, in a flower there is continuity in the vascular supplyof different whorls with that of the mother plant through the peduncle and pedicel.2.2 STERILE APPENDAGESSepals are more or less leaflike or bractlike in form, structure, and vasculature. Theyare usually green and rarely petaloid. Anatomically, the epidermis shows depositionof cutin and development of stomata and trichomes similar to those on foliage leaves.The mesophyll is undifferentiated or rarely differentiated into palisade and spongytissues.Petals vary in shape, size, and color. In most flowers, they form the mostconspicuous whorl and help in insect pollination. The epidermis bears stomata,functional or undifferentiated and nonfunctioning, and may develop intercellular
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 26: Reproductive Structures and Seed Fo
Page 29 and 30: 14 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
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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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