Inconsistency between SSR groupings and genetic backgrounds of white corn inbreds

Heterotic groups in white corn (Zea mays L.) are not well defined. Simple sequence repeats (SSRs) have been found useful for assigning inbreds to heterotic groups. Our objectives were (i) to determine whether simple sequence repeat (SSR) markers lead to clear groupings of white corn inbreds and (ii) to examine the consistency between SSR groupings and genetic backgrounds of white corn inbreds. We analyzed 18 white corn inbreds derived from five white corn populations (Pride of Saline, Jellicorse, Neal's Paymaster, Johnson County White, and Boone County White), four yellow corn inbreds derived from Iowa Stiff Stalk Synthetic (BSSS), and six non-BSSS yellow corn inbreds with 82 random SSR marker loci. The number of alleles per locus ranged from two to 11, with an average of five. Single crosses between white corn inbreds from different populations were nearly as diverse as the BSSS × non-BSSS yellow corn single crosses, i.e., the predominant heterotic pattern in yellow corn. Cluster analysis led to five groups of inbreds. The four BSSS inbreds (i.e., B14, B37, B73, and B84) were clustered in one group. But the four other groups comprised yellow and white corn inbreds from different populations. The first three principal components accounted for only 22% of the SSR variation among inbreds. The molecular marker data, therefore, underscored the lack of clear heterotic groupings among inbreds derived from open-pollinated cultivars of white corn. We speculate that white-endosperm conversions of BSSS inbreds could comprise one broad heterotic group, whereas non-BSSS white corn inbreds could comprise an opposite heterotic group.