Genetic variability among Nosema apis isolates

Genetic variability in the ribosomal RNA genes and the associated spacer re gions of Nosema apis was investigated in 13 New Zealand isolates and 12 iso lates obtained from around the world. Comparisons of banding patterns, obta ined by gel electrophoresis of polymerase chain reaction products amplified from the start of the intergenic spacer revealed marked variation among th e isolates. No differences were found among samples collected sequentially from particular colonies in New Zealand, nor among samples developed to min imize genetic diversity for further experiments. DNA sequence data were obt ained from around the internal transcribed spacer and from the 3' end of th e large subunit rRNA gene. No sequence variation was observed within or aro und the internal transcribed spacer. Only two single-base differences were identified in the DNA sequence from the large subunit rRNA gene; one in an isolate from Brazil and one in an isolate from Israel. The consequences of the variation observed are discussed.