MOLECULAR DIVERSITY OFnrDNA ITS REGIONAFFECTEDHETEROSIS INSUNFLOWER(Helianthusannuus)

Abstract

Astudy was conducted to specifymutationsof the internal transcribed spacer (ITS)inthe nucleotides of nuclear ribosomal DNA (nrDNA) and their molecular relationship withheterosisexhibitedby thesix A-lines and three R-testersof sunflower. The trailwas conductedatthe fields of the Collegeof Agriculture,University of Anbar,Abu Ghraib during twoseasons(spring and fall2016). Parental lines were crossed according to lineΧtester crossing schemeto produce 18 single hybrids,genotypeswere sowntoassess theirphenotypic performance in the fallseason.Results of the molecular analysis of ITSsequencing showed that the rearrangement of single nucleotides had accumulated ina higher rate in the F1hybrids compared with their ancestorinbreds. The total number of mutations was 268,anddeletion mutations accounted for the largest proportion with 209 mutation(71 in lines and 138 inhybrids). In contrast, the transition mutations were 25 all occurredin the hybrids, howeverthe number of transversionsrecorded 17only.Based on DNA sequence of thenrDNAITS region the total genotypes were separated into two main groups in cluster analysis following the nearest neighbor method. There was a significant convergence between R2 and both A4ΧR2 and A6ΧR3hybridsscoringhighervaluesof similarityin context ITS sequence. To be specific, the hybrid A2ΧR3exhibitedthe best desirable heterosisfordays to 75% floweringand leaf area, while hybrid A5ΧR3 hadthe highest heterosisforheadtraits,height and area.