Relationship between parental genetic distance and offspring’s heterosis for early growth traits in Liriodendron: implication for parent pair selection in cross breeding

Abstract

Parent-pair selection is one of crucial factors that generate progenies with strong heterosis in tree cross-breeding programmes. In our Liriodendron breeding programme, we conducted a very effective strategy on selecting elite parental combinations with strong heterosis on the basis of a large number of crosses and progeny tests. In the past two decades, we have conducted dozens of interspecies crosses in Liriodendron and the hybrids with good performance have been broadly planted for both ornamental and industrial utilization in southern China. In contrast to the application, the genetic mechanism of heterosis in Liriodendron still remains unknown. Genetic distance is one key parameter which has been considered for parent-pair selection. Here, we reported the relationship between parental genetic distance and offspring heterosis by analyzing early growth traits of progenies from intra- and inter-specific crosses in Liriodendron. The genetic distances among 13 parental trees were assessed based on polymorphisms generated from 24 microsatellites loci. Offspring heterosis was estimated based on a 6-year-old progeny test. No significant correlations were found between parental genetic distance and offspring heterosis. However, we found that the offspring heterosis of growth reached the maximum value when parental genetic distance was 1.07, which was validated in another batch of crosses based on 2-year-old growth. Our findings may be helpful for the future parent-pair selection in Liriodendron cross-breeding programmes.