SSR-based and grain yield-based diversity of hybrid maize in Thailand
Commercial hybrid maize varieties are often used to extract new inbred lines in hybrid breeding
programs. Seven commercial hybrid maize varieties were crossed in a diallel design, and the resulting
hybrids and selfed progeny were evaluated for yield and adaptability grown in six locations in Thailand.
The parental varieties were analyzed with a set of 64 Simple Sequence Repeat (SSR) loci, spanning all 10
chromosomes. The average number of alleles per SSR locus was 4.98 with a range of 2–11. The
polymorphic information content (PIC) varied from 0.24 to 0.89, with an average of 0.69. Using SSR-based
genetic distance (GD), an UPGMA dendrogram showed seven field corn varieties classified into three
distinct groups. Troyer’s genetic distance (TGD) calculated from yield data, which is a function of
inbreeding depression, varied from 0.493 to 1.015 between different parental combinations. A significant
positive correlation was found between the GD and TGD across the six locations (0.66**). The GD
correlated positively with specific combining ability (SCA) as well across all locations (r = 0.76**) heterosis
was significant for grain yield and SCA, accounting for 47% of the sum of the square among entries.
Therefore, we suggest that broad base populations derived from each of the distinct groups can be formed
using combined criteria of SSR-based GD, TGD, grain yield, GCA and SCA.