A proper choice of a dissimilarity measure is important in surveys investigating genetic relationships among germplasm with molecular marker data. The objective of our study was to examine 10 dissimilarity coefficients widely used in germplasm surveys, with special focus on applications in plant breeding and seed banks. In particular, we (i) investigated the genetical and mathematical properties of these coefficients, (ii) examined consequences of these properties for different areas of application in plant breeding and seed banks, and (iii) determined relationships between these 10 coefficients. The genetical and mathematical concepts of the coefficients were described in detail. A Procrustes analysis of a published data set consisting of seven CIMMYT maize populations demonstrated close affinity between Euclidean, Rogers’, modified Rogers’, and Cavalli‐Sforza and Edwards’ distance on one hand, and Nei's standard and Reynolds dissimilarity on the other hand. Our investigations show that genetical and mathematical properties of dissimilarity measures are of crucial importance when choosing a genetic dissimilarity coefficient for analyzing molecular marker data. The presented results assist experimenters to extract the maximum amount of information from genetic data and, thus, facilitate the interpretation of findings from molecular marker studies on a theoretically sound basis.

linkage (Stuber et al., 1992; Crow, 1999). Epistasis, particularly between linked loci, may also be an explanation Heterotic groups and patterns are of fundamental importance in for heterosis in maize (Cockerham and Zeng, 1996). No hybrid breeding of maize (Zea mays L.). The major goal of this study data exclude the possibility of all three mechanisms was to investigate the relationship between heterosis and genetic distance determined with simple sequence repeat (SSR) markers. The contributing to heterosis, albeit in different proportions. objectives of our research were to (i) compare the genetic diversity Lamkey and Edwards (1999) coined the term panmicwithin and between seven tropical maize populations, (ii) test alterna-Breeding, Seed Sci.,

sal et al., 1992a). However, the mixed genetic constitution of the populations and pools made the task of Detailed knowledge about the genetic diversity among germplasm assigning them to genetically diverse and complemenis important for hybrid maize (Zea mays L.) breeding. The objectives of our study were to (i) investigate the genetic diversity among tropical tary heterotic groups difficult. Nevertheless, the germlowland inbred lines and (ii) delimit heterotic groups in this germ-plasm was categorized based on their yield performance plasm. Simple sequence repeat (SSR) analysis of 79 markers distribinto different heterotic groups, and some promising hetuted uniformly throughout the maize genome was performed for 155 erotic patterns are under development in RRS programs tropical lowland inbred lines from the International Maize and Wheat (Vasal et al., 1999). Improvement Center (CIMMYT). Inbred lines were extracted fromSince its inception in 1984, the hybrid maize program 60 broad-based populations and pools with mixed origin. We observed of CIMMYT has developed and released 497 CIMMYT an average of 7.4 alleles per marker with a range from 2 to 18. The maize inbred lines (CMLs) derived from the above menpolymorphic information content (PIC) of the 79 SSRs ranged from tioned broad-based pools and populations. These CMLs, 0.13 to 0.87, with an average of 0.60. Cluster analysis of the tropical and CIMMYT germplasm in general, have played an yellow and white lines revealed a lack of structure within this germplasm, which can be explained by the mixed origin of the populations important role in hybrid maize production in developing used to extract these lines and the specific choice of testers for recipro-countries (Morris, 2001). The lowland tropical CMLs cal recurrent selection (RRS). An SSR analysis can support the choice were selected from approximately 60 populations or of representative testers for evaluating inbred lines in such broadpools based on their per se performance and combining based populations. Thus, a more complete exploitation of the outability when crossed to testers. Little information is standing flint-dent heterotic pattern is possible.

No abstract

BackgroundDoubled haploid production is a key technology in triticale research and breeding. A critical component of this method depends on chromosome doubling, which is traditionally achieved by in vivo treatment of seedlings with colchicine.ResultsIn this study we investigated the applicability of an in vitro approach for chromosome doubling based on microspore culture. Our results show a pronounced increase in the proportion of doubled haploid triticale plants compared to the spontaneous doubling rate, but also compared to the doubling obtained by the standard in vivo approach. In addition, the frequency of plants surviving from culture medium to maturity is also much higher for the in vitro approach. Colchicine concentrations of 1 mM for 24 h or 0.3 mM applied for 48 or 72 h during the first hours of microspore culture performed best.ConclusionsOur results suggest that for triticale, in vitro chromosome doubling is a promising alternative to the in vivo approach.