Inheritance of parental genomes in progenies of Poa pratensis L. from sexual and apomictic genotypes as assessed by RAPD markers and flow cytometry

Moving gene(s) responsible for the apomictic trait into crop plants that naturally reproduce through a sexual process would open up new areas in plant breeding and agricultural systems. Kentucky bluegrass (Poa pratensis L.) is one of the most important forage and turf grasses in temperate climates. It reproduces through facultative aposporous parthenogenesis, but the reproductive behaviour ranges naturally from nearly obligate apomixis to complete sexuality. In addition to apomictic reproduction, sexual hybridization may take place. Selfing may also occur, and occasionally reduced egg cells may develop through parthenogenesis generating (poly)haploids. The inheritance of parental genomes was assessed in Kentucky bluegrass progenies by employing RAPD markers in combination with flow cytometry (FCM). Nine progenies from different crosses carried out between completely sexual and highly apomictic genotypes were evaluated in order to probe the reproductive behaviour of the mother plants and to distinguish the different classes of aberrant plants. Not only were maternals and balanced B-II hybrids recorded, but so were (poly)triploid B-III hybrids, selfs, and (poly)haploids. The application of these techniques demonstrated that FCM analysis accurately distinguishes the n, 2n, and 3n ploidy levels of progenies, and that RAPD markers unequivocally recognize progenies of apomictic and hybrid origin. The occurrence of aneusomaty was documented in one of the selected sexual genotypes, whose crossed progeny plants manifested two distinct classes of ploidy. The nomenclature B-I was adopted to refer to hybrids with a hypodiploid nuclear condition. On the whole, the FCM analysis confirmed most of the RAPD data. The combined evaluation of DNA markers and DNA contents proved to be an efficient screening tool for scoring maternal plants, assessing the genetic origin of aberrant plants, and quantifying the inheritance of parental genomes in Kentucky bluegrass. Hybrid populations from sexual x apomictic matings that segregate for the mode of reproduction represent a valuable basis for attempting to identify molecular markers linked to the apomixis gene(s).