Relevance of unilateral and bilateral sexual polyploidization in relation to intergenomic recombination and introgression in Lilium species hybrids

Abstract

Sexual polyploids were induced in diploid (2n = 2x = 24) interspecific F1 hybrids of Longiflorum 9 Asiatic (LA) and Oriental 9 Asiatic (OA) Lilium hybrids by backcrossing to Asiatic (AA) parents as well as by sib-mating of the F1 LA hybrids. A majority of the BC1 progenies were triploid and the progenies from sib-mating were tetraploid or near tetraploids. Genomic in situ hybridization (GISH) technique was applied to assess the intergenomic recombination in the BC1 populations of LA and OA hybrids obtained after unilateral sexual polyploidization. A total of 63 LA (LA 9 AA and AA 9 LA) and 53 OA hybrids were analysed. LA hybrids were originated through the functioning of 2n gametes either as 2n eggs or 2n pollen while those of OA hybrids originated through functional 2n pollen of diploid OA genotype. In both type of crosses, a majority of the progenies had originated through First Division Restitution (FDR) mechanism of functional 2n gamete either with or without a cross over. However, there were nine LA-and four OA-genotypes where Indeterminate Meiotic Restitution (IMR) was the mechanism of 2n gamete formation. Based on GISH, total amount of introgression of Longiflorum and Oriental genome into Asiatic genome was determined. Most of the BC progenies exhibited recombination and the amount of recombination was higher in LA hybrids as compared to OA hybrids. Intergenomic recombination was also determined cytologically in the 16 plants of sib-mated LA hybrids where both parents had contributed 2n gametes. Based on these results the nature of interspecific lily hybrids obtained from uni-and bilateral sexual polyploidization leading to allotriploid and allotetraploid formation is discussed in the context of introgression and intergenomic recombination.

GISH analyses of backcross progenies of twoLiliumspecies hybrids and their relevance to breeding

“…The presence of aneuploid plants indicated that some aneuploid gametes in the OT and MA hybrids were viable. Similar results were also found in the LA and OA hybrids (Zhou et al, 2008;Khan et al, 2010). In triploid BC 1 plants, if there was no chromosome recombination, recessive genes would not be expressed.…”

“…In addition to crossing-over, there was a clear instance (in 092058-1) of recombination due to chromosome assortment resulting from IMR. Such an event has also been recorded in the BC 1 progenies of LA and OA hybrids (Lim et al, 2001a;Barba-Gonzalez et al, 2005a;Khan et al, 2010).…”

“…In Lilium, previous studies have shown that some of the genotypes of F 1 LA and OA interspecific hybrids possess a level of fertility resulting from the production of functional 2n gametes (Karlov et al, 1999;Lim et al, 2001a;Zhou et al, 2008;Barba-Gonzalez et al, 2005a, b;Khan et al, 2010;Van Tuyl et al, 2002b). It was possible to generate triploid BC 1 progenies from all these 2n gamete-producing F 1 hybrids by crossing the diploid F 1 hybrid to one of the parents.…”

Use of 2n Gametes in Plant Breeding

“…This results in a narrow selection of cultivars from mitotic polyploidization. In contrast, analytic breeding strategies allow intergenomic recombination to produce triploid Lilium varieties (Khan et al, 2009;Khan et al, 2010). Other examples of analytical breeding for crop improvement are vegetatively propagated species such as potato, sweet potato, cassava, among roots and tubers, and plantain/banana (Ortiz, 2002).…”

Assessment of intergenomic recombination through GISH analysis of F1, BC1 and BC2 progenies of Tulipa gesneriana and T. fosteriana

“…It would be instructive to compare the recombination pattern in the F1 hybrids or BC progenies of species that possess large amounts of C-banded heterochromatin, such as tulip, with those that possess much less of such heterochromatin, such as Lilium, both of which we have investigated extensively (Lim et al 2003;Barba-Gonzalez et al 2005Zhou et al 2008;Khan et al 2009Khan et al , 2010Xie et al 2010). Both Tulipa and Lilium have many biological characteristics in common: both belong to the family Liliaceae; both species possess huge amounts of nuclear DNA with 2C DNA values ranging from 65.5 to 86.4 pg in Lilium (Bennett 1972) and from 32 to 69 pg in Tulipa (Zonneveld 2009), and consequently very large chromosomes.…”