STRUCTURE AND INHERITANCE OF RIBOSOMAL DNA VARIANTS IN CULTIVATED ANDWILD HOP, HUMULUS-LUPULUS L

Genetic variation was assessed among cultivated and wild hop, Humulus lupulus, by restriction fragment length polymorphisms (RFLPs) of the r ibosomal RNA genes (rDNA). Two rDNA length variants of 10.3 and 9.3 kb p represented by three phenotypes designated A, B and C were detected with XhoI. Restriction-site mapping showed that hop rDNA is structural ly similar to those of most higher plants. A high level of homogeneity existed in rDNA repeat lengths among the diverse hop genotypes. Gener ally, phenotype A was predominant in wild and cultivated European and Asian genotypes; phenotype B in North American cultivars; while phenot ype C was present only in native North American hop, providing a poten tial molecular marker for the identification of this germ plasm. The r DNA data provided genetic evidence for the separation of native and cu ltivated American genotypes and supports the hypothesis that North Ame rican hop cultivars are of hybrid origin from European and native Amer ican genotypes. The segregation of rDNA phenotypes in four F-1 familie s suggests that a single locus with two co-dominant alleles controls g enetic variability for rDNA variants in hop.