Intergenomic recombination and introgression breeding in Longiflorum x Asiatic lilies
Lily, one of the economically most important ornamental crops, belongs to the genus Lilium of the family Liliaceae. There are about 80 species in Lilium which are categorized into seven sections, i.e., Lilium, Martagon, Pseudolirium, Archelirion, Sinomartagon, Leucolirion and Oxypetala. Usually, it is not so difficult to cross between the species within each section and the hybrids are fertile. However, it is very difficult to cross the species belonging to different sections. With cut style pollination followed by embryo rescue techniques, such distant interspecific crosses can be possible, but the hybrids are highly sterile. All modern lily cultivars have originated from hybridization among wild lily species. The three main lily cultivar groups, viz., Longiflorum, Asiatic and Oriental, originated from hybridization within one section, i.e., Leucolirion, Sinomartagon and Archelirion respectively. Up to now, about 150 Longiflorum, 4000 Asiatic cultivars, and 2000 Oriental cultivars have been registered. The genomes of Longiflorum (Leucolirion), Asiatic (Sinomartagon) and Oriental (Archelirion) are represented as L (Longiflorum), A (Asiatic) and O (Oriental) genome respectively. They possess quite different valuable traits, and one of the main goals of modern lily breedingareto combine the three distinctive groups in new cultivars. In this thesis, crosses among diploid Asiatic and Longiflorum cultivars, diploid F1 LA hybrids, triploid BC1 cultivars, allotetraploidand allopentaploid lilies were made. 11 diploid F1 LA hybrids and 19 triploids BC1 cultivars which were supplied by the Dutch lily breeding companies, and 23 new BC1, five BC2 and seven BC3 progenies were analyzed with conventional cytological methods, flow cytometry and genomic in situ hybridization.The configurations of metaphase I during meioses of the F1 LA hybrids are quantitatively variable, ranging from no bivalent to 12 bivalents in different pollen mother cells. This implies that LA hybrids have abnormal meiosis and normal meiosis, and indicates that LA hybrids have possibilities to produce aneuploid gametes, 2n gametes and n gametes (Chapter 2). Because the bivalents disjoin and the univalents divide simultaneously at anaphase I of the observed pollen mother cells, it is concluded that F1 LA hybrids have more potential to produce IMR 2n gametes than FDR 2n gametes I (Chapter 2). However, most of the BC1 progenies result from FDR 2n gametes and less from IMR 2n gametes. Probably, FDR 2n gametes have better viability than IMR 2n gametes because of chromosome and gene imbalance in the latter (Chapters 3 & 4).Besides the mode of 2n gamete formation, some crossover events, e.g., single, threestranddouble, four strand double, four strand triple crossover, etc, are clearly elucidated based on the GISH results from anaphase I of F1 LA hybrids (Chapter 2). The intergenomic recombinant chromosomes of triploid BC1 progenies mainly originate from single crossover (Chapters 3 & 4). The intergenomic recombinant chromosomes caused by other crossover events are confirmed in diploid BC1 progenies (Chapter 4).Based on GISH analysis of 19 BC1 cultivars from the Dutch lily breeding companies, 17 of the BC1 cultivars are eutriploid and two hypertriploid (Chapter 3). Nevertheless, among 45 new BC1 progenies, 10 of them are diploid, while the others are triploid (Chapter 4). This is the first reported finding that LA hybrid can produce functional haploid gametes. This finding might be valuable for lily introgression breeding. Only limited BC2 progenies, which originated from crosses between triploid BC1 cultivars and diploid Asiatic cultivars, were analyzed with GISH. They were predominantly diploid and they contained very few Longiflorum chromosomes or segments (Chapter 5).Allopentaploid lilies have relatively good male fertility as determined from their pollen germination. They were successfully crossed with Asiatic cultivars and Longiflorum cultivars. Most of the BC3 progenies were pseudoeuploids that possessed euploid chromosome numbers (2n=3x=36) but the parental genomes were aneuploid as a result of chromosome substitutions. Apart from this, one aneuploid (2n=3x+1=37) was also present. Both the pseudoeuploids and the aneuploids might contribute to genetic variation and are potentially useful for selection. Based on the results of lily interploid crosses (2x-3x, 2x-4x, 2x-5x and their reciprocals), diploid, triploid, tetraploid, and pentaploid lilies could be used as male parents when they had some degree of male fertility. Most diploid and triploid lilies could be used as female parents regardless of their male fertility. On the contrary, allotetraploid and allopentaploid lilies could hardly be used as female parents even though they had good fertility as estimated from pollen germination tests. The success and failure of interploid crosses in lilies depends on the viability of the gametes and the ploidy level of the secondary nucleus. From the process of tetrasporic eight-nucleate embryo sac formation in Lilium , it is derived that diploid, triploid, tetraploid, and pentaploid lilies produce tetraploid, hexaploid, octaploid and decaploid secondary nuclei in their embryo sacs respectively. Thus, It is suggested that tetraploid secondary nucleus might be ideal for lily endosperm development; hexaploid secondary nucleus are acceptable; but octaploid or higher secondary nuclei are not ideal (Chapter 5).The difference between 2x-4x and 4x-2x or 2x-5x and 5x-2x is obvious, because one was successful and the other not. A clear difference was also observed between 2x-3x and 3x-2x and between AA x LA and LA x AA. The difference is possibly caused by the frequency of functional gametes, ploidy level of endosperm and the interaction between embryo development and endosperm development (Chapter 5).2n gametes and n gametes might play different roles in lily breeding. The former is more useful for polyploid breeding; the latter may be valuable for introgression breeding. We could not over- or underestimate either of them, because the LA hybrids which could produce functional 2n gametes or n gametes are very limited. Especially, it is more difficult to find LA hybrids which produce functional n gametes. The advantages of 2n gametes over mitotic doubling in lily breeding have been well confirmed (Chapters 3 and 4). One of the further tasks is how to use the LA hybrids which produce viable n gametes in lily breeding.
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| Format: | Doctoral thesis biblioteca |
| Language: | English |
| Subjects: | crosses, crossing, genomes, interspecific hybridization, introgression, lilium, plant breeding, recombination, sporogony, genomen, introgressie, kruisen, kruisingen, plantenveredeling, recombinatie, soortkruising, sporogenie, |
| Online Access: | https://research.wur.nl/en/publications/intergenomic-recombination-and-introgression-breeding-in-longiflo |
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