Abstract
Deleterious epistatic interactions in plant inter- and intraspecific hybrids can cause a phenomenon known as hybrid necrosis, characterized by a typical seedling phenotype whose main distinguishing features are dwarfism, tissue necrosis and in some cases lethality. Identification of the chromosome regions associated with this type of incompatibility is important not only to increase our understanding of the evolutionary diversification that led to speciation but also for breeding purposes. Development of molecular markers linked to the lethal genes will allow breeders to avoid incompatible inbred combinations that could affect the expression of important agronomic tratis co-segregating with these genes. Although hybrid necrosis has been reported in several plant taxa, including Rosaceae species, this phenomenon has not been described previously in pear. In the interspecific pear population resulting from a cross between PEAR3 (Pyrus bretschneideri × Pyrus communis) and ‘Moonglow’ (P. communis), we observed two types of hybrid necrosis, expressed at different stages of plant development. Using a combination of previously mapped and newly developed genetic markers, we identified three chromosome regions associated with these two types of lethality, which were genetically independent. One type resulted from a negative epistatic interaction between a locus on linkage group 5 (LG5) of PEAR3 and a locus on LG1 of ‘Moonglow’, while the second type was due to a gene that maps to LG2 of PEAR3 and which either acts alone or more probably interacts with another gene of unknown location inherited from ‘Moonglow’.
Highlights
Hybrid necrosis (HN) is the reduced viability of a hybrid due to genetic incompatibilities
Screening with molecular markers enabled us to identify ß 2016 Nanjing Agricultural University three chromosome regions associated with this phenomenon
Segregation analysis of phenotypes showed that BDM-like incompatibilities involving epistasis amongst different loci were the basis of HN in this pear population, a finding that is consistent with reports for other plant species.[6,47,48]
Summary
Hybrid necrosis (HN) is the reduced viability of a hybrid due to genetic incompatibilities. Interactions between genes may have a positive effect on the hybrid, resulting in it having better performance than its parents (hybrid vigour), they may be detrimental and cause sterility, weakness or lethality.[1] Genetic incompatibilities can occur at different stages of the reproduction process, and they are generally divided into prezygotic and postzygotic, acting, respectively, before and after fertilization. HN, which is termed hybrid weakness or inviability, is a class of postzygotic gene-flow barrier that is associated with a typical seedling phenotype, characterized by cell death, tissue necrosis, wilting, yellowing, chlorosis, dwarfism and reduced growth rate, and in some cases lethality.[2,3] HN has been observed in several plant taxa, in wild and cultivated species and both in inbred populations and outcrosses; its phenotype appears to be characteristic across a range of hosts, suggesting a common underlying mechanism.[2,3]. Most of the cases of HN reported in the literature are explained by a two-gene epistasis[2,5]; there are some examples of three-locus interactions[6] and lethality controlled by a single locus.[7,8,9]
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