Interspecific hybridisation and genome size analysis in Buddleja

Abstract

Interspecific hybrids Buddleja davidii x Buddleja weyeriana, Buddleja weyeriana x Buddleja davidii and Buddleja davidii x Buddleja lindleyana were generated using in vitro embryo rescue 10-11 weeks after manual pollination. The morphological variation within the F1 populations was limited. The F1 progeny of B. davidii x B. lindleyana was almost sterile and no F2 generation was obtained. From the other hybrids, F2 generations were made by self pollinations and back crosses. Hybrid nature of all F1 and F2 seedlings was confirmed by AFLP. Chromosome counting and genome size measurement for B. weyeriana (F2 selection of (diploid) B. globosa x (tetraploid) B. davidii) revealed a higher chromosome number (76 chromosomes) and genome size than expected, indicating 2n-gametes formation occurred during meiosis of B. globosa. The F1 hybrids B. weyeriana x B. davidii (76 chromosomes) had an intermediate genome size compared with the genome size of the parent plants, proving their hybrid nature. However, the F1 and F2 hybrids of B. davidii x B. weyeriana all had 76 chromosomes but had a lower genome size than expected, suggesting the occurrence of chromosome rearrangements in the genome of the hybrids. B. lindleyana had 38 chromosomes, while the F1 hybrids of B. davidii x B. lindleyana had 76 chromosomes. Also genome size measurements revealed that the F1 seedlings B. davidii x B. lindleyana had higher genome sizes than expected. Both the results of chromosome counting and genome size measurement indicate that 2n-gametes formation took place during meiosis of B. lindleyana

Introgression of yellow flower colour in Buddleja davidii by means of polyploidisation and interspecific hybridisation

“…Buddleja species exist with 38 (B. globosa), 76 (B. davidii) and even up to 228 chromosomes. Great variation in interspecific genome size was also reported (Moore 1960;Hanson et al 2001;Zonneveld et al 2005;Van Laere et al 2009). The high genetic variability in Buddleja presents considerable opportunities to develop novel cultivars through interspecific crosses.…”

“…The ploidy levels of treated seedlings and shoots and genome sizes of parent plants and F1 progeny were measured according to Van Laere et al (2009). For the measurements of the genome sizes, the reference plant Pisum sativum cv.…”

“…Interspecific crosses were performed as described in Van Laere et al (2009). Chromosome doubled B. globosa GLO9 (obtained via droplet method with 0.3mM TRI) and GLO34 (obtained via seed sowing method with 1mM ORY) were used as male parent.…”

“…On 10 fully developed inflorescences of a genotype (parental species and F1 hybrids) the length and/ or diameter of the inflorescence was measured. Fertility of a genotype was evaluated by analysing seed set and pollen germination capacity according to the protocol described in Van Laere et al (2009).…”

“…The high genetic variability in Buddleja presents considerable opportunities to develop novel cultivars through interspecific crosses. Controlled interspecific hybridisation in Buddleja was first reported by Van De Weyer (1920) (Moore 1949;Leeuwenberg 1979;Tobutt 1993;Dirr 1998;Elliott et al 2004;Lindstrom et al 2004;Van Laere et al 2009). Nevertheless, the differences in ploidy level and genome sizes within Buddleja species can limit the success rate of interspecific hybridisation.…”