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

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Location of Fungal Hyphae in Seeds 141establishes in seeds of beet and spinach. Huang, Hanna, and Kokke (1985) observedV. albo-atrum throughout the stems of alfalfa, but it occurred only sporadically inthe peduncle, pedicels, pods, and seeds. Artificial inoculation of stigmas of healthyplants of cultivar Vernal of Medicago sativa (alfalfa) caused infection of the stigmaand upper part of style. The infection remained confined to these parts throughoutthe fruit and seed development. Under humid conditions, the fungus in the remnantsof style attached to the mature pod, rarely invaded the pod and seed coat (Huang,Hanna, and Kokke, 1985). Christen (1982) found V. albo-atrum hyphae in alfalfaseeds, particularly small seeds obtained from artificially inoculated greenhouseplants of susceptible cultivars. SEM photomicrographs showed the mycelium withinand between hourglass cells of the seed coat.Artificial inoculation by injecting spore-mycelium suspension of V. albo-atrumin stems of Lupinus albus and L. luteus showed variability in the colonization offruit and seed. The pathogen was discontinuous in tissues of fruit, including funiculusin L. albus. It was confined to the seed coat, but not seen in vascular elements. InL. luteus, mycelium occurred in vascular bundles of the seed coat, within the tracheidbar and the funicular trace in infected seeds. Profuse mycelium occurred in the spacebetween the seed coat and embryo and from there it spread to the cotyledons (Parnisand Sackston, 1979).5.5.4.1.10 TrichotheciumTrichothecium roseum, a well-known saprophyte, is common in seeds of crop plants.It causes seed rot and seedling blight in incubation tests in maize kernels (Singh,Singh, and Singh, 1985), seeds of cowpea (Varma and Singh, 1991), and rape andmustard (Sharma, 1989). The seeds are asymptomatic or symptomatic. In cowpea,rape, and mustard, symptomatic seeds show discoloration and shiny pinkish myceliumand/or conidia on the seed surface. In maize kernels, thin, shining hyalinehyphae colonized the basal cap, pericarp, endosperm, and embryo. The infectedembryo was well formed, but thin with lysigenous cavities containing abundantmycelium and bicelled spores of T. roseum.In symptomatic seeds of cowpea, T. roseum occurred in the seed coat, endosperm,and embryo. The mycelium was inter- and intracellular in hourglass cells and formeda thick mat in parenchyma cells and spongy parenchyma in the hilar region. Theembryonal infection occurred in the peripheral layers of cotyledons, radicle, and allover in the plumule and seminal leaves (Varma and Singh, 1991). In rape and mustardthe mycelium of T. roseum was confined to the epidermis and subepidermis of theseed coat in symptomless and bold weakly discolored seeds. In heavily discoloredseeds, however, it occurred in the seed coat, endosperm, and embryo. The myceliumwas inter- as well as intracellular and caused depletion of cell contents (Sharma,1989). The symptomatic seeds in cowpea and heavily discolored and shriveleddiscolored seeds of rape and mustard failed to germinate.5.5.4.2 Coelomycetes5.5.4.2.1 ColletotrichumColletotrichum species, which cause anthracnose and die-back diseases, have mostlyGlomerella and occasionally Physalospora or some other genus as the sexual stage.
142 Histopathology of Seed-Borne InfectionsColletotrichum lindemuthianum was the first seed-borne fungus whose myceliumwas found to penetrate deep into the cotyledons of bean (Phaseolus vulgaris) byFrank (1883). Colletotrichum spp. are commonly encountered in seeds of legumes,solanads, and cereals (Richardson, 1990).Chili seeds infected with Colletotrichum dematium have a few to many brownto black spots (acervuli) on the seed surface (Chitkara, Singh, and Singh, 1990). Inmoderately infected seeds, the mycelium is usually confined to the seed coat, spacebetween seed coat and endosperm, and superficial layers of endosperm. Hyphaerarely invaded the embryo. Inter- and intracellular hyphae and acervuli occurred inthe seed coat, endosperm, and embryo in heavily infected seeds (Table 5.5). Thickseptate mycelium covered the seed surface and spread among spaces between differentcomponents of seed. A thick mat of mycelium was found in parenchymatouslayers of the seed coat, the comma stem region of endosperm, and the radicle endand tips of cotyledons, which lie close to the comma stem region (Chitkara, Singh,and Singh, 1990). Symptomatic seed showed only 53% germination and 32% seedlingsurvival.Chikuo and Sugimoto (1989) observed variations in the establishment ofC. dematium f. sp. spinaceae mycelium in seeds obtained from plants of Beta vulgarisartificially inoculated at early and late flowering stages. In the former condition,infection spread in the fruit cavity, and hyphae invaded developing seed, causing itscollapse. But in the latter situation, the mycelium was usually confined to the surfaceof the seed ball, and hyphae were rarely seen in the apical pore and under the seedcoat.Tiffani (1951) artificially inoculated seeds of soybean with C. dematium andobserved pre-emergence killing, seedling blight, and plants with latent infection. Infruits of plants with latent infection, fungal hyphae were traced in the carpel wall,ovary cavity, and in the cotyledons of developing seeds. Initially these pods weresymptomless, but at maturity, some of them were covered with acervuli. Schneideret al. (1974) found that C. dematium mycelium in symptomatic soybean seeds fromIndia is confined to the hourglass layer of the seed coat and to naturally occurringwounds.Varma, Singh, and Singh (1992c) and Bhatia et al. (1996b) found that heavyinfection of Colletotrichum dematium occurred in all components of categorizednaturally infected seeds of Vigna aconitifolia and Cyamopsis tetragonoloba, respectively(Table 5.5). Varma, Singh, and Singh (1992c) found hyphae occurring on orin the palisade cells, hourglass cells, and, rarely, in the peripheral layers of the hilarregion in moderately infected seeds. The hyphae in the heavily infected seeds weredistributed all over in the seed, i.e., in the seed coat-palisade cells, the hourglasslayer, and the parenchyma layers, the embryo-cotyledons and hypocotyledonaryroot-shoot axis, and in the hilar region in all tissues, including the tracheid bar andspongy parenchyma. Heavily infected seeds failed to germinate.Basu Chaudhary and Mathur (1979) recorded C. graminicola in the pericarp (97and 83%), horny (24.6 and 39.2%) and floury endosperms (8.6 and 14.2%), andembryos (1.4 and 1.3%) of two seed samples of sorghum. About 55% of seeds didnot germinate, showing severe seed rot. Of the emerging seedlings, the majority
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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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192 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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