ABSTRACT
It is generally considered that closely related organisms share a greater nucleotide sequence similarity than those that are distantly related. A highly specific nucleotide sequence present in an isolate or strain of virus or other pathogen, but absent from other strains or species, may be used to test for the presence of that virus or pathogen. Detection of plant pathogens by hybridization is based on the production of nucleic acids by specific hybridization between the single-stranded target nucleic acid sequence (denatured DNA or RNA) and a complementary singlestranded nucleic acid probe. Probes for plant viruses are mostly cDNA, as the genomes of most plant viruses are RNA. Either RNA or DNA sequences may be used as probes. Transcription vectors to produce RNA probes in vitro can be developed to yield RNA:RNA or RNA:DNA hybrids, which are more stable than DNA:DNA hybrids.
