Drought tolerance and genetic diversity among tropical maize inbred lines

Drought stress is a major constraint especially to tropical maize production and accurate classification of the elite lines for drought response and genetic diversity is critical for the success of the maize breeding programs. The main objectives of this study were to: (i) classify drought/heat-selected and drought-unselected maize inbred lines by their drought response using field and greenhouse experiments, (ii) analyze the genetic diversity of these maize inbred lines using DNA-based markers, and (iii) determine the population structure among the lines defined by the DNA markers. Drought response of 15-drought tolerant, one-drought susceptible and 14-maize inbred lines with unknown response to drought were evaluated in side-by-side experiments under well-irrigated and managed-drought stress conditions in three-field locations of Mexico, and one greenhouse experiment. In the field and greenhouse experiments, nine agronomic traits were recorded, including grain yield. The genetic diversity among the maize lines was studied utilizing 62 RFLP probes and 52 SSR markers distributed throughout the maize genome. Path analyses showed that female flowering, anthesis-silking interval, ears per plant, kernels per ear, and 100-kernel weight were the most important traits determining the grain yield across water regimes. Principal component (PCA) and cluster analyses (CA) were used to determine the relationship between lines based upon their drought response. These two methods of statistical analyses showed similar results identifying only one group comprised predominantly of drought/heat tolerant lines. These lines showed highest performance under drought condition. A relative high level of genetic diversity was found among lines, since the number of alleles per locus detected by the RFLP and SSR markers was 7.2 and 5.2, respectively. Associations among lines based on DNA markers were assessed using PCA and CA, thus detecting similar groups of lines, which were mostly in agreement with the genetic origin or breeding program. Results indicated that drought tolerant lines can be present among conventionally selected lines, and that RFLP and SSR markers are useful for studying the relatedness among high diverse inbred lines