INHERITANCE OF CHROMOSOMAL LENGTH POLYMORPHISMS IN THE ASCOMYCETE LEPTOSPHAERIA-MACULANS

Pulsed field gel electrophoresis experiments show that chromosomal len gth polymorphisms are produced during meiosis in the ascomycetous plan t pathogen Leptosphaeria maculans. Homologues in tetrads of L, maculan s were identified on the basis of their binding to chromosome-specific probes that included P-tubulin, nitrate reductase, 18S ribosomal DNA and two Random Amplified Polymorphic DNA (RAPD) markers. Changes in si ze of homologues were followed during meiosis. Significant karyotype v ariation was evident due to the random assortment of parental homologu es of different sizes. In most cases, the progeny had the same-sized h omologues as the parents; however, in some instances novel-sized homol ogues were detected that varied in size from those of the parents by u p to 50 kb. Our results are consistent with the hypothesis that these novel chromosomal length polymorphisms are produced by reciprocal reco mbination between parental homologous chromosomes of unequal sizes.