CHANGE IN RIBOSOMAL DNA INTERGENIC SPACER-LENGTH COMPOSITION IN MAIZERECURRENT SELECTION POPULATIONS .1. ANALYSIS OF BS13, BSSS, AND BSCB1

Five different ribosomal DNA (rDNA) intergenic spacer-length variants (slvs) were detected among the maize inbreds which were the progenitor s of Iowa Stiff Stalk Synthetic (BSSS). One rDNA SstI restriction site polymorphism in the 3' region of the 26S gene was detected. Nine diff erent rDNA intergenic spacer (IGS) hybridization fragment patterns (as signed letter designations A-I) were observed among the BSSS progenito rs. Following 7 cycles of half-sib recurrent selection in BSSS using t he Ia13 double cross as a tester, hybridization fragment pattern E bec ame predominant in the population. In contrast, 11 cycles of reciproca l recurrent selection in BSSS with the Iowa Corn Borer Synthetic No. 1 (BSCB1) population resulted in hybridization pattern D becoming predo minant. Hybridization pattern E is present in the elite inbreds B14, B 37, B73, and B84, which were derived from different cycles of the BSSS half-sib recurrent selection program with Ia13. Hybridization pattern D is present in the elite inbreds B89 and B94, which were derived fro m different cycles of the BSSS reciprocal recurrent selection program with BSCB1. Therefore, two different forms of recurrent selection on B SSS resulted in different hybridization patterns becoming predominant in the selected populations and present in elite inbreds derived from the populations. These results also suggest that rDNA IGS hybridizatio n fragment patterns D and E, which both have the longest slv detected, may have a selective or adaptive advantage in BSSS materials grown in the Corn Belt.