Genetic diversity among CIMMYT maize inbred lines investigated with SSR markers: I. lowland tropical maize

Detailed knowledge about the genetic diversity among germplasm is important for hybrid maize (Zea mays L.) breeding. The objectives of our study were to (i) investigate the genetic diversity among tropical lowland inbred lines and (ii) delimit heterotic groups in this germplasm. Simple sequence repeat (SSR) analysis of 79 markers distributed uniformly throughout the maize genome was performed for 155 tropical lowland inbred lines from the International Maize and Wheat Improvement Center (CIMMYT). Inbred lines were extracted from 60 broad-based populations and pools with mixed origin. We observed an average of 7.4 alleles per marker with a range from 2 to 18. The polymorphic information content (PIC) of the 79 SSRs ranged from 0.13 to 0.87, with an average of 0.60. Cluster analysis of the tropical yellow and white lines revealed a lack of structure within this germplasm, which can be explained by the mixed origin of the populations used to extract these lines and the specific choice of testers for reciprocal recurrent selection (RRS). An SSR analysis can support the choice of representative testers for evaluating inbred lines in such broad-based populations. Thus, a more complete exploitation of the outstanding flint-dent heterotic pattern is possible.
FEW AGRONOMIC IMPROVEMENTS during the 20th century rival the development of hybrid maize (Brummer, 1999). Yields in maize increased dramatically as breeders moved away from open-pollinated cultivars and began developing [...]