Heterosis, inbreeding depression and genetic divergence in maize

Abstract

Heterosis refers to the superiority of the hybrid over its parents. Heterosis depends on non-additive gene effects and in the difference in allele frequencies between parents. The objective of this experiment was i) to test a model of heterosis based on dominance, genetic divergence in allele frequency between the parents (Δ), and inbreeding depression, ii) to estimate the contribution of  and the inbreeding depression in the parents to heterosis, and iii) to estimate the genetic importance of a hybrid seed production system for grain yield, plant height, and ear height. Our results showed that a single-locus model with two alleles explains the variability in each generation and was suitable to predict heterosis in maize. Midparent heterosis (MH) is a function of Δ and dominance, while inbred-midparent heterosis depends on Δ, dominance, and inbreeding depression. There was a negative relationship between MH and inbreeding depression. Inbreeding depression is expected to be high in panmictic populations, however, when FST approaches unity inbreeding depression is reduced to zero. Lower midparent values and higher MH were obtained when the parents were inbred to homozygosity, with a limiting value being an inbred line. Reduced heterozygosity, which results in low inbreeding depression, could be understood as the underlying basis of heterosis. Consequently, the recovery from inbreeding depression because of the masking of recessive alleles could result in high heterosis.