Genetic relationships among CIMMYT subtropical QPM and Chinese maize inbred lines based on SSRS

Forty six maize inbred lines, including 22 CIMMYT QPM lines and 24 Chinese lines, were investigated with SSRs in the study. The objectives of this research were to: (1) investigate the genetic diversity among the 46 inbred lines, (2) assess the genetic distance between subtropical and Chinese Quality Protein Maize (QPM) inbred lines and (3) estimate the genetic relationships between subtropical QPM and Chinese normal inbred lines. In total, 64 simple-sequence repeats (SSRs) primers distributed uniformly throughout the maize genome were considered. The mean value (0.66) of the polymorphic index content (PIC) for the SSR loci provided sufficient discrimination ability for the assessment of genetic diversity among the inbred lines. The mean estimates of genetic similarity (GS) among the 18 Chinese normal maize lines (0.344) and among the six Chinese QPM lines (0.486) were significantly higher (P < 0.01) than the mean GS among 22 CIMMYT QPM lines (0.310). Chinese normal maize lines and QPM lines were considered to have a narrower genetic diversity than the CIMMYT QPM lines. The result of GS estimates among CIMMYT subtropical QPM lines indicated that these lines were derived from such a broad-based germplasm that some lines with a similar pedigree showed large genetic distances. The average-linkage (UPGMA) cluster analysis classified the 46 inbred lines into two main clusters. Most Chinese normal maize lines were classified into a large cluster and most CIMMYT subtropical QPM lines were grouped in a different cluster. These results indicated that incorporating CIMMYT subtropical QPM lines into Chinese maize germplasm according to their genetic relationships would enhance the genetic basis of the latter.