NUCLEAR RIBOSOMAL DNA UNIT LENGTH VARIATION - A PUTATIVE MARKER OF GENETIC DIVERSITY IN JOJOBA

jojoba (Simmondsia chinensis [Link] Schneider) is a crop of high econo mic interest that is grown for the exceptional quality of its seed oil . We have taken advantage of the large variation commonly shown by rib osomal DNA (rDNA) in many plant species to assess the genetic diversit y between clones and among individuals in jojoba. The variation of rDN A was analyzed with the use of a homologous 1.7-kbp probe generated by PCR and a 20-mer oligonucleotide probe targeting, respectively, the 1 7S and 25S coding regions. The multiple-step ladder obtained with the BamH I-EcoR I restriction fragment containing the intergenic spacer (I GS) was the best indicator of variation in length of rDNA unit. In add ition to variations observed among selected clones, significant differ ences in the relative proportion of length variants were seen among in dividuals grown from seeds of unknown origin.