Lemons: Diversity and relationships with selected citrus genotypes as measured with nuclear genome markers

inter-simple sequence repeats (ISSR), simple sequence repeats (SSR) and iso zymes were used to measure genetic diversity and phylogenetic relationships among 95 Citrus L, accessions including 57 lemons [C. limon (L.) Burm. f,] , related taxa, and three proposed ancestral species, C. maxima (Burm.) Mer rill (pummelo), C. medica L. (citron), and C. reticulata Blanco (mandarin), The ancestry of lemons and several other suspected hybrids was also studie d. Five isozyme and five SSR loci revealed relatively little variation amon g most lemons, but a high level of variation among the relatively distant C itrus taxa. Eight ISSR primers amplified a total of 103 polymorphic fragmen ts among the 83 accessions. Similarity matrices were calculated and phyloge netic trees derived using unweighted pair-group method, arithmetic average cluster analysis. All lemons, rough lemons, and sweet lemons, as well as so me other suspected hybrids, clustered with citrons. Most lemons (68 %) had nearly identical marker phenotypes, suggesting they originated from a singl e clonal parent via a series of mutations. Citrons contributed the largest part of the lemon genome and a major part of the genomes of rough lemons, s weet lemons, and sweet limes. Bands that characterize C. reticulata and C. maxima were detected in lemons, suggesting that these taxa also contributed to the pedigree of lemon.