Improvement trends, phenotypic and molecular diversity among hard red winter wheat cultivars in Nebraska

The first chapter deals with the genetic improvement trends in agronomic performances and end-use quality attribute in the Nebraska hard red winter wheat cultivars. The aim of the study was to determine genetic variability and trends of genetic progress in agronomic and end-use quality traits and assess stability and association between characters if there were changes over time. Thirty cultivars including 5 historically important ancestors released from 1784 to 2000 were evaluated under rain-fed conditions at Lincoln, Mead and North Platte in 2002 and 2003 seasons using alpha lattice design with 45 incomplete blocks of two plots. Modern cultivars were high yielder, highly responsive to environments and less stable for grain yield and its components when compared to older lines. Older cultivars showed more response than modern cultivars for days to flowering and plant height. Breeders have selected lines for higher grain yield and spike productivity, earliness, shorter height, higher flour yield, longer mixing time and mixing tolerance. Chapter II focused on the comparison of genetic diversity estimates using different methods in the same cultivars. The study objectives were to (1) determine the genetic diversity among had red winter wheat cultivars adapted to the Northern Great Plains using pedigree information, morphological traits, end-use quality attributes and molecular markers and (2) examine the association of genetic distance estimates obtained from these methods. Genetic diversity was estimated based pedigree history, morphological traits and end-use quality traits, seed storage proteins, 51 SSRs and 23 SRAPs. Molecular markers showed that pedigree analysis had overestimated genetic distance between cultivars due to unrealistic assumptions. All distance estimates were positively interrelated. Highly significant positive correlation of distance estimates from morphological traits with all other method showed relation of morphological diversity with end-use quality and molecular markers diversity. Highly significant positive correlation between molecular markers-based distances estimates shows that molecular markers could explain similar genetic variability among cultivars. Relatively, clustering based on SSR markers and morphology grouped most cultivars in agreement with pedigree history