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

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Location of Fungal Hyphae in Seeds 147in discolored, heavily infected seeds (Figure 5.2A). The internal infection may varyin seeds of the same category in different cultivars. In symptomatic seeds, thepericarp is always infected, but the infection gradually decreases from outside toinside in seeds of each category, even in the same cultivar (Table 5.6). Usually inbold symptomless seeds having a loose pericarp (weakly infected), hyphae areconfined to the pericarp, but in shriveled and discolored seeds, hyphae are frequentlypresent in all tissues, e.g., cultivar Svenno, but in cultivar Starke II, no infection wasseen in the testa, aleurone layer, endosperm, or embryo in shriveled seeds, and thesecomponents were only rarely invaded in discolored seeds (Table 5.6).Varma, Singh,and Singh (1991) determined the distribution of hyphae of an unidentified Stagnosporasp. in decoated rubber seeds. The pathogen colonized the tegmen, perisperm,endosperm, and embryo. The fungus caused lysigenous cavities in the endospermand embryo, containing abundant mycelium.5.5.4.2.8 RhizoctoniaRhizoctonia species are soil inhabitants. They are both soil-borne and seed-borne.Rhizoctonia species, particularly Rhizoctonia bataticola and Rhizoctonia solani,have a very wide host range and are internally seed-borne in a variety of hosts (Table5.5). The seeds infected with R. bataticola (Sclerotium bataticola) are mostly symptomaticand occasionally symptomless. The symptomatic seeds have black pinheadlikemicrosclerotia on the seed surface. Their number is directly correlated with theseverity of infection and also with the internal infection and damage caused to seedtissues (Singh and Singh, 1979; Kunwar et al., 1986b; Mathur, 1992; Varma, Singh,and Singh, 1992a,b; Bhatia, Singh, and Singh, 1998).In seeds of different leguminous crops, the course and extent of infection of R.bataticola is basically similar (Table 5.5). In soybean seeds, the fungus is readilyobserved on the outer and inner surfaces of the seed coat in SEM photomicrophs.Hyphae are seen penetrating through cracks, micropores, and the funiculus (Mathur,1992). In asymptomatic seeds, fungal hyphae are confined to the seed coat and hilartracheids. Thick, branched, septate, inter- and intracellular mycelium, and microsclerotiaoccur in all the layers of the seed coat in weakly, moderately, and heavilyinfected symptomatic seeds. In heavily infected seeds hyphae traverse horizontallyand vertically in cells of seed components and also in spaces between components.Cotyledons are invaded from adaxial as well as abaxial surfaces. In the hilar regionabundant mycelium occurs on either side of the counter palisade layer, in the tracheidbar, and stellate parenchyma. The fungus causes lysis of cells, cell vacuolation andnecrosis, and formation of sclerotia in the cotyledons, radicle, and plumule inseverely infected seeds. TEM micrographs show necrosis of the cell wall, enlargementof protein bodies with pronounced changes in optically dense and stainedbodies, which become unrecognizable, digestion of lipid bodies, loss of discretenessin cell organelles, and appearance of ergastic bodies with surface striations, usuallyseen along the cell wall and plasma membrane (Mathur, 1992).Basu Chaudhary and Pal (1982) found infection of M. phaseolina in all parts ofsunn hemp seeds. In seeds of Cyamopsis tetragonoloba, having well-developedendosperm, R. bataticola infection occurs in all components (Bhatia, Singh, and
TABLE 5.6Location of Mycelium of Stagnospora nodorum in Different Categories of Seeds of Two Wheat SamplesSeed CategoriesEpicarpSample No. 1 (Cv. Svenno)PericarpHypodermCross Cell LayerTestaAleurone LayerEndospermEmbryoPericarpSample No. 2 (Cv. Starke II)Bold seeds 4 4 1 0 0 0 0 3 2 0 0 0 0 0Seeds with loose and 5 4 3 0 0 0 0 5 3 1 0 0 0 0cracked pericarpShriveled seeds 5 5 3 2 2 2 2 5 4 2 0 0 0 0Discolored seeds 5 5 5 3 3 3 3 5 5 2 1 1 1 1Note: Evaluated using microtome sections, five seeds per category.From Agarwal, K., Singh, T., Singh, D., and Mathur, S.B. 1985. Phytomorphology 35: 87–94.EpicarpHypodermCross Cell LayerTestaAleurone LayerEndospermEmbryo148 Histopathology of Seed-Borne Infections
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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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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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230 Histopathology of Seed-Borne In
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