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

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Seed Infection by Bacteria 175vbbBDbxypcvbvbbCbExyfubAFGFIGURE 6.4 Path of movement of bacteria in plant after artificial inoculation. A to D, Clavibactermichiganensis ssp. michiganensis in young tomato plant. A, Diagram from plant collectedafter 5 days of inoculation. Arrow indicates the point of inoculation and solid black areas, theprimary vascular bundles that carry bacteria. B, Cross section from the main axis of theinoculated plant. Solid black areas represent bacteria in and around xylem. C, Bacteria in vessel.D, Bacterial pocket formed by escape of bacterial cells from a vessel into the surroundingintercellular spaces and xylem parenchyma. E to G, Pseudomonas syringae pv. lachrymans innaturally infected cucumber fruit tissues. E, F, Bacteria in and between parenchyma cells andwithin xylem in the mesocarp, respectively. G, Bacteria invading the parenchyma cells of thefuniculus. (Abbreviations: b, bacteria; fu, funiculus; pc, parenchyma cells; vb, vascular bundle;vbb, vascular bundle with bacteria; xy, xylem elements.) (A to D, from Pine, T.S., Grogan, R.G.,and Hewitt, Wm. B. 1955. Phytopathology 45: 267–271; E to G, from Wiles, A.B. and Walker,J.C. 1951. Phytopathology 41: 1059–1064. With permission.)
176 Histopathology of Seed-Borne Infectionsmade by them. However, earlier observations by Wiles and Walker (1951) of thesame pathogen showed that the bacterium advanced intercellularly as well as withinxylem elements of the fruit mesocarp (Figure 6.4E, F) after invasion through thestomata. Zaumeyer (1932) has also noted the movement of P. s. pv. phaseolicolathrough the xylem and parenchyma tissues of bean plants.The above information reveals that the ovary and fruit infection may take placefrom the mother plant via vascular elements or through intercellular spaces in theparenchyma. Local infection of any part of the fruit including the pedicel may alsobecome vascular if it gains entry into xylem elements, or it may spread in intercellularspaces, or both. Whether vascular, or from intercellular spaces, the infection canreach the ovule either through the funiculus, which connects ovule and seed to thefruit at the placenta, or it may enter the ovary and fruit cavity after breaking thewall. In the latter condition, bacterium may spread on the ovule surface in part orcompletely, and it may enter the ovule through the micropyle and ovule surfacedirectly or through the stomata, if present, as in Gossypium and Hibiscus.X. axonopodis pv. phaseoli in beans enters the ovule and seed through thevascular elements and also the parenchyma of the funiculus or from the bacterialmass occurring in pod cavity. In cases of severe funicular infection, its tissuesdegrade and the ovule and seed failto develop. If weak to moderate infection takesplace at a late stage of seed development, the bacterium spreads in the seed coatand around the cotyledons. Bacterial mass in the pod cavity surrounding or occurringin the vicinity of the ovule and seed may easily invade through the micropyle(Zaumeyer, 1930). In 1932 Zaumeyer found that C. f. pv. flaccumfaciens also entersthe ovule through the vascular elements in the funiculus or through the micropyle.After the bacterium has escaped from the vessels in the funiculus and the dorsalsuture and the parenchyma of the pod wall, it may gain entry into the micropyle.Skoric (1927) found invasion of pea seeds by P. s. pv. pisi through the parenchymatouscells of the funiculus and also through the micropyle (Figure 6.8A, B;see p. 186). In the pea pod, abundant bacterial mass also occurs on the inner sideof infected pods. Although Skoric (1927) reports that the micropylar infection occursfrom the funiculus, its invasion from the bacterial mass present in the pod cavitycannot be ruled out. Seed infection in cucumber by P. s. pv. lachrymans occursthrough bacteria growing intra- and intercellularly (Figure 6.4G) in the funiculus(Wiles and Walker, 1951). In the mesocarp of the fruit it is detected in xylem elementsand also in parenchyma (Figure 6.4E, F). However, Wiles and Walker (1951) couldnot detect the bacterium in seed. But Nauman (1963) observed that P. s. pv. lachrymanspenetrates through the funiculus and micropyle and spreads in the seed coat,endosperm, and embryo. X. c. pv. campestris also reaches cabbage seed through thefuniculus as shown by Cook, Larson, and Walker (1952) in artificially inoculatedplants. The invasion is systemic and spreads through the vascular system in pedicelsand siliculas. The bacterial mass was observed throughout the funiculus up to itsjunction with the seed and it disrupted the xylem in severely affected areas.In artificially inoculated tomato plants with Clavibacter michiganensis subsp.sepedonicus, Larson (1944) found that the pathogen entered the fruit through thevessels and/or tracheids in the fleshy placenta to the funiculus of the seed. Fukuda,
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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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100 Histopathology of Seed-Borne In
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Page 224 and 225: Seed Infection by Viruses 209Wilcox
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Page 232 and 233: Seed Infection by Viruses 2177.4.2
Page 234 and 235: Seed Infection by Viruses 219seed(s
Page 236 and 237: Seed Infection by Viruses 221AMV fo
Page 238 and 239: 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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