Genetic Diversity of Corn Hybrids from Different Sources in Thailand as Verified by Their Heterotic Pattern and Inbreeding Depression

Abstract

Growing a single cross or single crosses of genetically related inbreds in a large area has proved to be vulnerable to biological and physical hazards and lead to crop disaster when such genetic background became susceptible to ever changing environment. The purpose of this study was to measure genetic diversity of twelve commercial hybrids in Thailand. The genetic diversity was estimated by the formula : GD = 1 – [(H-C)/(H-S)], where GD, H, C and S stand for genetic diversity, average performance of the two hybrids, hybrid by hybrid cross, and average of the self-hybrids, respectively. The method assumes that heterosis is caused by cummulated effect of dominance and absence of epistasis. Theoretically, Two closely related hybrids with a GD of 0.25 should have one common inbred and other two inbreds are genetically related. Two hybrids with one inbred in common and the other two unrelated inbreds have the expected GD of 0.5. Two slightly related hybrids with a GD of 0.75 should have one related inbred and other two distinct inbreds. Two unrelated hybrids have an expected GD of 1.0. The estimation of genetic diversity of 12 commercial hybrids indicated that pairs of hybrids from the same company such as CP 999 x CP 888 (GD=0.25) and Pioneer 3013 x Pioneer 3012 (GD=0.26) each has closely related inbreds on both sides of the pedigree. Other three pairs of hybrids, Cargill 922 x Cargill 919 (GD=0.51), Pacific 700 x Pacific 328
(GD=0.57) and Uni. 98 x Uni-H 9728 (GD=0.67) each should have one inbred in common. The hybrids from different companies have GD in the range of 0.37–0.98 such as CP 999 x Cargill 919 (GD=0.37), SW 3853 x Pioneer 3013 (GD=0.75), Pacific 700 x Cargill 922 (GD=0.97), G5445A x Pioneer 3013
(GD=0.96), Uni-H 9728 x Cargill 919 (GD=0.96) and Cargill 922 x Uni. 98 (GD=0.98). The results showed that, the hybrids in Thai market still had considerable genetic diversity with noticeably exchanged of genetic background.