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

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Location of Fungal Hyphae in Seeds 145and heavily infected seeds, abundant mycelium occurred in various tissues, includingvascular elements in the tegmen. It formed a thick mycelial mat in the spaces aroundthe endosperm and embryo. In heavily infected seeds, B. theobromae caused disintegrationof cells. Some of the mesophyll cells in infected cotyledons becamehypertrophied and thick-walled (Varma, Singh, and Singh, 1990).5.5.4.2.4 DiplodiaHeald, Wilcox, and Pool (1909) reported that Diplodia zeae is internally seed-bornein maize kernels. The dormant mycelium occurs in the endosperm and embryo.Miller’s (1952) report that the fungal mycelium first invades the embryo and subsequentlyspreads to the endosperm and pericarp needs confirmation.Diplodia gossipina, which causes black boll rot in cotton, infects seed and lint,making them smutty (Crowford, 1923; Crosier, 1944; Roncadori, McCarter, andCrawford, 1971). Snow and Sachdev (1977) observed that D. gossipina enters cottonbolls through the epidermis, multicellular hairs, and stomata to reach the ovary andfruit cavity.5.5.4.2.5 PhomaPhoma lingam, which causes blackleg in oilseed and vegetable crucifers, expressesas crown canker, stem canker, and leaf lesions. The disease is seed-borne and seedtransmitted (Petrie and Vanterpool, 1974; Gabrielson, 1983). In cabbage seeds,P. lingam is common in the outer epidermis and subepidermal parenchyma andoccasionally in other layers of the seed coat. It is frequently found in the peripherallayers of cotyledons and only rarely infects the radicle (Jacobsen and Williams,1971). Phoma lingam infection survives for more than 10 years in vegetable cruciferseed (Gabrielson, 1983).Hyphae and pycnidia of Phoma lycopersici, which causes stem rot in tomato,are located in spaces left by the absorption of the parenchymatous cells of the middlezone of the seed coat (Fischer, 1954).Rastogi, Singh, and Singh (1991) reported that seeds of different cultivars ofsorghum infected by Phoma sorghina bear black, pinhead-like pycnidia on thesurface. Their number correlates directly with the severity of infection. Sorghumseeds are with or without testa. Bold asymptomatic seeds with or without testa werefree of infection. Seeds without testa had weaker infection than those with testa.Symptomatic seeds with testa carried thick, dark brown, and septate mycelium inthe epicarp and mesocarp, and only occasionally invaded the endocarp in weaklyinfected seeds. In moderately infected seeds, inter- and intracellular myceliumoccurred in all layers of the pericarp and rarely spread in the hilar region, aleuronelayer, transfer cells (modified endosperm cells), and peripheral layers of the scutellum.Pycnidia were common on the seed surface and in the pericarp. Abundanthyphae and pycnidia occurred in the pericarp, testa, aleurone layer, and endospermin heavily infected seeds. The infection in the endosperm proceeded centripetally,and the mycelium formed a network around the cells in floury endosperm. Embryonalinfection was moderate to heavy, and abundant mycelium and pycnidia occurred allover (Rastogi, Singh, and Singh, 1991).
146 Histopathology of Seed-Borne Infections5.5.4.2.6 PhomopsisPhomopsis spp. cause blight, stem canker, leaf spot, and fruit rot in many vegetable,ornamentals, fruit, and other economic crops. In soybean Phomopsis spp. complexcomprising Diaporthe phaseolorum var. sojae, D. phaseolorum var. caulivora, theirPhomopsis anamorphs and an unidentified species cause seed decay. Ilyas et al.(1975) reported hyphae of Phomopsis sp. in the seed coat and cotyledons of soybean.Subsequently, Singh and Sinclair (1986) observedi the mycelium of Phomopsis sp.on the surface and in various layers of the seed coat in naturally infected seeds, i.e.,palisade cells, hourglass cells, and parenchyma cells. It also occurred in the hilarregion, including the stellate parenchyma and tracheid bar, aleurone layer, otherlayers of endosperm, and the embryo (cotyledons). Hyphae formed a thick mat inthe seed coat parenchyma and endosperm and also colonized the space around theembryo and between the two cotyledons.Phomopsis heveae, which causes die-back of stem and mature seed pods, is acommon seed-borne fungus of Hevea brasiliansis (Richardson, 1990; Singh andSingh, 1990). Decoated infected seeds may be symptomless or discolored, light todark brown. The symptomless infected seeds carry thin and hyaline mycelium inthe tegmen, endosperm, and space between the endosperm and embryo. The hyphaeare relatively thick, inter- and intracellular in the above tissues in light brown seeds.The dark brown discolored seeds (heavy infection) contain hyphae in all seedcomponents. In the tegmen, hyphae also occur around vascular bundles and invascular elements, particularly the vessels. Abundant inter- and intracellular myceliumis seen in the perisperm, endosperm, and embryo. The embryo is surroundedby a mycelial mat, and cotyledonary infection is more on the abaxial side than theadaxial side (Varma, Singh, and Singh, 1991).5.5.4.2.7 Septoria and StagnosporaDiseases caused by these fungi are worldwide and affect many crops. The mostcommon and most serious disease is leaf and glume blotch in wheat, caused byStagnospora nodorum. It is seed-borne and seed transmitted. Important seed-borneSeptoria spp. are S. glycines in Glycine max, S. linicola in Linum, S. apiicola incelery and parsley, and S. lactucae in Lactuca. The pycnidia are present on seedsof celery and parsley (Neergaard, 1979). Dormant mycelium of S. glycines andS. linicola occurs in the seed coat of soybean and flax seeds, respectively (Lafferty,1921; Sinclair and Backman, 1989).Wheat seeds infected by S. nodorum form an important source of primaryinoculum for leaf and glume blotch disease. The seed-borne infection may survivefor 10 or more years, depending upon the storage conditions (Hewett, 1987; Siddiquiand Mathur, 1989; Cunfer, 1991). Ponchet (1966) reported the occurrence ofS. nodorum mycelium beneath the testa (probably the pericarp) of diseased wheatkernels, but Kietreiber (1961) found that all seed tissues, including the embryo, maybe colonized in severely damaged seeds. Agarwal et al. (1985) found that wheatseeds infected by S. nodorum may be symptomless (bold) or symptomatic, havinga loose cracked pericarp, shriveling, and discoloration. The hyphae of S. nodorumare confined mostly to the pericarp in bold and cracked seeds, to the pericarp andaleurone layer in shriveled seeds, and are found in all the parts, including the embryo,
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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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14 Histopathology of Seed-Borne Inf
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3Structure of SeedsThe seed habit i
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Structure of Seeds 49(1971) of usin
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Structure of Seeds 51is found in as
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Structure of Seeds 53dry seed of Ly
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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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196 Histopathology of Seed-Borne In
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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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