Oriental lily hybrids engineered to resist aphid attack

Establishing in vitro bulb scale cultures of lily cultivars followed by callusing and regeneration after gene transfer was found to be not very successful in our hands, except for ‘Snow Queen’. Identifying a more generally applicable system to generate callus with the ability to regenerate and amenable to Agrobacterium-mediated gene transfer was the goal of the research described here. Callus was induced on style and filament explants of 26 cultivars of lily. The cultivars were chosen from the hybrid groups longiflorum, asiatics and orientals of the genus Lilium but also interspecific hybrids were represented. Most cultivars were diploids but some were of triploid level and one was tetraploid. In general once callus was induced, it could relatively easily be maintained and propagated for further use. Regeneration was observed on both callus types from all cultivars tested with an efficiency ranging from 40 to 100%. Gene transfer as demonstrated by positive reporter gene uidA activity was found in all cultivars tested. Transgenic plants could be obtained in the first series of transformations and the applicability of a marker-free system was proven in lily. The protocol can now be used for the introduction of genes aiming at conferring resistance to aphids

Interspecific lily hybrids: a promise for the future

In order to introduce new characters such as resistances, flower shape and colour, from wild species into the cultivar assortment of lily it is necessary to overcome interspecific crossing barriers.. Several techniques have been used for wide interspecific lily crosses with species and cultivars from the different sections of the genus Lilium (L. longiflorum, L. henryi, L. canadense L. concolor, L. dauricum, L. candidum, L. rubellum, L. martagon, Asiatic and Oriental hybrids). Hybrids originating from intersectional crosses (e.g. L. longiflorum x L. concolor, L. longiflorum x L. dauricum, L. longiflorum x L. henryi, L. longiflorum x L. martagon, L. longiflorum x L. candidum, L. longiflorum x Asiatic hybrids (LA), L. longiflorum x Oriental hybrids (LO), L. longiflorum x L. rubellum, L. longiflorum x L. canadense, Oriental x Asiatic hybrids (OA) and L. henryi x L. candidum) have been produced. Especially the Oriental x Asiatic hybrids are a break-through in lily breeding and a promise for the future. In general wide interspecific lily hybrids show F1-sterility. Using chromosome doubling techniques tetraploids with restored fertility are produced from these diploid hybrids. At this moment a crossing programme at polyploid level with these hybrids is being carried out

Introgression of Lilium rubellum Baker chromosomes into L. longiflorum Thunb.: a genome painting study of the F1 hybrid, BC1 and BC2 progenies

Interspecific hybrids between Lilium longiflorum (L, 2n = 2x = 24) and Lilium rubellum (R, 2n = 2x = 24) were produced with the aim of transferring desirable horticultural traits from L. rubellum to L. longiflorum. All F1 hybrids (LR, 2n = 2x = 24) and BC1 individuals (LLR, 2n = 3x = 36) were phenotypically uniform for plant height, flowering time, leaf shape and flower colour. The BC1 plants were, in spite of their triploid nature, fertile and could be used as a female parent in backcrossmgs with autotetraploid L. longiflorum (LLLL, Zn = 4x = 48). Twelve BC2 individuals were obtained and three of them were selected for further chromosome analysis. As L. longiflorum and L. rubellum chromosomes were indistinguishable in the hybrids, genomic in-situ hybridization (GISH) was applied to establish the parentage of the chromosomes of the F1 hybrids and the BC1 and BC2 progenies. GISH confirmed the LLRR constitution of the doubled amphimonoploid (allodiploid), and the LLR constitution of all BC1 plants. The three selected BC2 plants were, as expected, aneuploid, containing three complete sets of L. longiflorum chromosomes and six, seven or eight L. rubellum chromosomes, respectively. However, L/R translocation or recombinant chromosomes could not be demonstrated in the mitotic metaphase complements of the F1, BC1 and BC2 plants. In spite of the high frequencies of homoeologous recombination in the F1 hybrids (LR) pollen was found to be sterile in all cases. At metaphase I of the pollen mother cells of the BC1 plants, genome painting did not reveal any cases of homoeologous pairing and recombination between L and R chromosomes. This lack of exchange between homoeologous chromosome segments indicates complete preferential pairing of the L and R chromosomes in the F1 (amphidiploid) and BC1 plants. It seems that the preferential pairing in the F1 and BC1 hybrids hinder the introgression of the chromosome segments or species-specific genes into the recipient for breeding purposes