ABSTRACT
Seed infection is the establishment of a pathogen within any part of a seed, which may occur systemically, either through the vascular system or plasmodesmatic connections or directly through floral infection or penetration of the ovary wall, seed coat, or natural openings. Infection of any single seed may take place by more than one process. For example, bean seed infection by X. c. pv. phaseoli can occur through the vascular system of a systemically infected plant, by suture infection followed by invasion of the funiculus, raphe, and/or seed coat, or through the micropyle. 1 Entry into seeds from a mother plant may occur by (l) the pathogen colonizing the spikelets from an infected boot leaf while the panicle is still enclosed, (2) infected glumes providing inoculum after panicle emergence, or (3) the pathogen entering through the hilar region from infected vascular tissue.2 Infection by Peronospora parasitica conidia of the stigma and of the ovary wall and establishment of infection in the ovary of radish have been reported. 3 Infection through the stigma and ovary results in embryonic infection. A direct correlation has been found between embryonic infection and seed transmission of the downy mildew fungus. 3
theinductionandaccumulationofthePRmsproteins(pathogenesis-relatedproteins).TheincreaseisduetoanincreaseintranslatablePRmsmRNA.5PSbMV infectioncanbelatentthroughthevegetativephaseandreachrelativelyhigh concentrationsinfloralpartsandseeds.ThusPSbMVmaybemaintainedathigh levelsinseedsintheabsenceofsymptomsintheplantandwithouttransmission betweenplantsbyvectors.6
