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

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Location of Fungal Hyphae in Seeds 149Singh, 1998). In sunflower, infection is common in the pericarp and endosperm, butrare in the embryo (Raut, 1983; Godika, Agarwal, and Singh, 1999).Singh and Singh (1979) observed that M. phaseolina causes usually symptomaticand rarely symptomless infection in sesame seeds. In symptomatic seeds, profusethick, knotty, dark brown to black, and septate mycelium and also microsclerotiawere seen in all components and also between the spaces among the components(Figure 5.16C to F). Weak infection induced cell divisions in the endosperm andembryo, quite characteristic in the palisade cell region of cotyledons (Figure 5.3A,B). Heavy infection resulted in abundant aggregation of mycelium and microsclerotiain seed components and depletion of food contents (Figure 5.16F).Hedgecock (1904) first reported Rhizoctonia solani to be internally seed-bornein beans. Mycelium and sclerotia were present in the seed coat of seeds obtainedfrom pods in contact with soil. Baker (1947), who examined seeds of Capsicumfrutescens from rotted fruits that were in contact with soil, found R. solani asmycelium and sclerotia on the surface of the seed coat and as mycelium in theremnants of the funiculus, seed coat, endosperm, and embryo, particularly at the tipof the radicle. Chitkara, Singh, and Singh (1986b) observed R. solani mycelium andmicrosclerotia in the seed coat and endosperm in seeds of C. annuum obtained fromfruits borne on plants above the soil surface.5.6 ENDOPHYTESEndophytic fungi constitute an interesting group present in conifers to grasses(Alexopoulos, Mims, and Blackwell, 1996). Taxonomically they belong to Hypocreales(Clavicipitaceae), Loculoascomycetes, and Inoperculate Discomycetes(Rhytismatales). The term endophyte has been defined as an organism contained orgrowing entirely within a plant, parasitically or symbiotically (Snell and Dick, 1971;Siegel, Latch, and Johnson, 1987). The endophytic fungi, which are seed-borne andbelong to the tribe Balansiae of the Clavicipitaceae (Diehl, 1950; Siegel, Latch, andJohnson, 1987), are considered here. The infection is systemic, and nonhaustorialand intercellular mycelium occur in all parts of the affected plant except roots.The presence of endophytic mycelium in seed of a grass (Lolium temulentum)was first reported by Vogl (1898). Sampson (1933, 1935, 1937) showed the maternaltransmission of the endophyte. This has been confirmed on E – ¥ E + pair crosses byNeill (1940, 1941), Siegel et al. (1984a, 1985), and Manuel and Do Valle (1993).The effects of the fungal endophytes on the reproductive cycle of their hosts vary,ranging from complete sterility to complete fertility. There is an inverse correlationof host and fungus sexuality. In parasitic associations, the fungus is sexual (producesboth ascospores and conidia) and the host is asexual or with serious derangementsin the reproductive cycle. In symbiotic or mutualistic associations, the host is sexual(produces viable seeds) and the fungus is asexual (Clay, 1986). The behavior of thesame endophyte may also vary in different hosts (Sampson, 1935).Table 5.7 gives information on infection of endophytes in flowers and seeds ofgrasses. The taxonomic identity of the endophyte in many of these cases has notbeen determined. Latch, Christensen, and Samuels (1984) isolated five endophytesof Lolium and Festuca in New Zealand and discussed their taxonomy and taxonomic
150 Histopathology of Seed-Borne InfectionsTABLE 5.7Fungal Endophytes in Reproductive Structures and SeedsPathogenHostPart(s) of Seedand FruitImportant ReferencesEpichloe typhina Festuca rubra Developing ovaries,seed-pericarp,endosperm, embryoE. typhina Dactylis glomerata Stromatic sheath aroundinflorescence, totallyor partially suppressedpanicles: seeds in thelatter abortive orcontained mycelium inall partsE. typhina(Acremoniumtyphinum)UnidentifiedendophyteUnidentifiedendophyteSampson, 1935Western and Cavett, 1959Agrostis hiemalis Seed including embryo White and Chambless,1991Lolium perenne Nucellus, periphery ofaleurone layerLolium perenne InflorescenceFestuca arundinacea primordium, floralapices, ovary, ovule,embryo sac, seedpericarp,aleuronelayer, endosperm,embryo includingplumule apexPseudocercosporella Trichachne insularis Scutellum, coleoptiletrichachinicolaand embryonic leavesAcremonium Festuca arundinacea Between seed coat andcoenophialumaleurone layerA. lolii Lolium perenne Between seed coat andaleurone layerLloyd, 1959Philipson and Christey,1986White and Morrow, 1990Manuel et al., 1994Manuel et al., 1994relationships with previously reported unidentified fungal endophytes. The endophytesidentified are Acremonium lolii (A. loliae) and a Gliocladium-like speciesfound in Lolium perenne, A. coenophialum, and Phialophora-like species in Festucaarundinacea, and Epichloe typhina in Festuca rubra.5.6.1 STROMATIC INFECTIONMany grasses and sedges are infected by endophytes that produce a stromatic sheatharound the panicle. Epichloe typhina produces a stromatic sheath that almost completelycovers the panicle in Dactylis glomerata (Cocksfoot grass). Usually thepanicle is completely suppressed, but it is rarely partially emerged. The partiallyemergent panicles have ovules and developing seeds that are invaded by fungal
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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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