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

182 Histopathology of Seed-Borne InfectionsTABLE 6.1 (CONTINUED)Seed Infecting Bacterial PathogensBacteria Host (Disease) Seed PartImportantReferencesC. flaccumfaciens pv.flaccumfaciens (Hedges)Collins and Jones(Corynebacteriumflaccumfaciens pv.flaccumfaciens (Hedges)Dowson)Pantoea stewartii subsp.stewartii (Smith)Mergaert et al. (Erwiniastewartii (Smith) Dye)Pantoea agglomerans(Beijerinck) Gavini et al.(E. herbicola (Lohnis)Dye)Phaseolus, Glycine(bacterial wilt)Zea (bacterial wilt,Stewart’s disease)Oryza (bacterial paleabrowning)CurtobacteriumPantoeaRaphe, seed coat Burkholder, 1930;Zaumeyer, 1932;Schuster and Sayre,1967; Schuster andSmith, 1983Chalaza, endosperm Rand and Cash, 1921;Ivanoff, 1933Lemma, palea Tabei et al., 1988discoloration varied from small water-soaked to slimy brown spots or general browningof seeds. Occasionally brownish sticky ooze occurred on the seed surface ofsymptomatic seeds. Histopathology of infected seeds revealed direct correlationbetween the severity of infection and internal invasion of tissues. In infected boldseeds, the bacterium usually occurred in the seed coat and rarely in the endosperm.But in bold-discolored and shriveled-discolored seeds, the bacterium was found inthe seed coat, endosperm, and embryo (Figure 6.5A, B). The distortion of seedtissues was greater in shriveled seeds than in bold-discolored seeds. The embryowas relatively small and thin in the former, and the infection was extra- as well asintraembryal. Symptomatic infected seeds on germination produced seedlings withbrown-black necrotic spots on the cotyledons.Mihail, Taylor, and Versluses (1993) detected X. campestris pv. campestris insiliqua and the surface of seeds of Crambe abyssinica. Zaumeyer (1930) foundinvasion of X. a. pv. phaseoli in bean seed through the xylem in the funiculus and/ormicropyle. Infection occurred in intercellular spaces in the seed coat and also in thespace around the embryo. No infection was seen in the cells of the palisade andhourglass layers of seed coat. It is only at the time of seed germination that thebacteria enter into the cotyledons.Sharma et al. (2001) have described the location of Xanthamonas a. pv. cajaniin seeds of pigeon pea. Seed infection varied from weak to severe and severelyinfected seeds were small and shriveled (Figure 6.6). In asymptomatic infected seeds,bacteria occurred in the palisade, hourglass cells, and parenchyma of the seed coat.