A quick methodology to identify sexual seedlings in citrus breeding programs using SSR markers

In citrus breeding and genetics, it is very important to distinguish betwee n zygotic and nucellar seedlings in order to eliminate unwanted genotypes. Usually, isozyme markers have been employed to determine the genetic origin of young plants. In this work we propose the use of SSR markers as an alte rnative methodology and compare them with isozymes in this kind of screenin gs. Two different populations were analysed: one derives from an interspeci fic cross and the other from selfing. We conclude that, in most cases, micr osatellites are more efficient than isozymic markers to identify the sexual origin of citrus seedlings, given their higher level of polymorphism and t he scarce number of polymorphic isozymes in some populations. We describe a quick and efficient methodology for SSR analysis, including a fast DNA ext raction in microcentrifuge tubes, and visualization through silver staining , which eliminates the need for a labelling step.