RAPD marker diversity in smooth bromegrass cultivars and selected populations

The level of genetic diversity within and among early smooth bromegrass (Bromus inermis Leyss.) cultivars is unknown. The objective of the first study was to investigate and characterize genetic diversity of smooth bromegrass cultivars and selected populations based on randomly amplified polymorphic DNA (RAPD) markers. A dendrogram constructed from average linkage cluster analysis did not indicate any clear pattern of division based on discrete or putative climatype or adaptation zones. However, there was considerable correspondence to known pedigree relationships revealed from previous smooth bromegrass morphological clustering analysis, particularly for lines that are closely related to each other. All groups of smooth bromegrass germplasm were found to have high within-population genetic variation that ranged from 84% to 96% of the total, reflecting the outcrossing reproduction and probably the complex inheritance of smooth bromegrass. Analysis of molecular variance showed the largest inter-population genetic variation for contemporary germplasms, supporting morphological studies for the existence of genetic variability in contemporary smooth bromegrass germplasms. These results suggest that landrace cultivars likely remain useful for germplasm improvement and cultivar development. Neutral detergent fiber (NDF) is considered the laboratory measure most closely correlated with voluntary intake. The objectives of the second study were to create smooth bromegrass populations divergent for NDF concentration in four smooth bromegrass base populations, and to identify RAPD marker changes in populations divergently selected for NDF. Two cycles of divergent phenotypic selection led to significant linear responses in NDF means among cycles across all populations. Principal components analysis separated selected populations into two distinct and contrasting groups of high and low NDF, reflecting divergence created as a result of selection for NDF. LOGISTIC regression identified eight RAPD fragments statistically associated to quantitative trait loci (QTL) for NDF concentration across selected populations. One marker AG14.0825 had significant linear responses across all four base populations of smooth bromegrass, due to change in marker allele frequency, accounting for 86 to 96% of the variation among cycle. These results demonstrate the efficiency of phenotypic divergent selection, and the utility of RAPD techniques not only for evaluating genetic relationships, but also for detecting QTL in smooth bromegrass populations.