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

Seed Infection by Bacteria 171ACBFDEGFIGURE 6.1 Stomatal penetration and vascular invasion by Xanthomonas axonopodis pv.phaseoli in bean. A to E, Stomatal penetration showing bacteria in the substomatal cavity andspreading from there into intercellular spaces. A, B, Leaf. C, D, Stem. E, Pod. F, Cs of midribregion of leaf showing bacteria in the xylem vessel. G, Cs stem showing invasion of metaxylemvessels by bacteria. (From Zaumeyer, W.J. 1930. U.S. Dept. Agric. Bull. 180: 1–36.)In addition to the stomata, C. m. subsp. michiganensis enters tomato leavesthrough trichomes (Layne, 1967). Getz, Fulbright, and Stephens (1983) alsoobserved that P. syringae pv. tomato entered tomato ovaries during the anthesisthrough eglandular and glandular hairs (Figure 6.2A to C). After the separation oftrichomes, the open trichome bases also served as sites for infection (Figure 6.2D).Meier (1934) studied early infection of Xanthomonas c. pv. campestris in cabbageand cauliflower and showed that the bacterium enters through the hydathodes. Thefire blight bacterium, Erwinia amylovora, invaded flowers of pear and apple througha noncutinized surface of stigma and anthers, hydathodes on sepals, stomata on thestyle, and sepals and nectarthodes on hypanthium (Hildebrand and MacDaniels,1935). After artificial inoculation of pear and apple flowers by E. amylovora, Pierstorff(1931) and Rosen (1935) found that the most common site of infection wasthrough the nectariferous surface of hypanthium. Thomson (1986) observed thatE. amylovora occurs predominantly on the stigmas of flowers in Pyrus, Malus,