The epidemiology and management of seedborne bacterial diseases.

Although seed production has been moved to semiarid regions to escape seedborne pathogens, seedborne bacterial diseases continue to be problematic and cause significant economic losses worldwide. Infested seeds are responsible for the re-emergence of diseases of the past, movement of pathogens across international borders, or the introduction of diseases into new areas. Considerable attention has been paid to improving the sensitivity and selectivity of seed health assays by using techniques such as flow cytometry and the polymerase chain reaction. There has also been progress in understanding infection thresholds and how they influence seed sample size determination and ultimately the reliability of seed health testing. Disease development and dissemination of pathogens from contaminated seedlots can be predicted using formulas that take into account inoculum density and environmental pressures. In general, seeds infested with bacterial pathogens are distributed within a Poisson distribution. In a subset of contaminated seeds, bacteria are distributed in non-Gaussian distributions, e.g., a lognormal distribution.