Genome size analysis in the genus Cucurbita and its use for determination of interspecific hybrids obtained using the embryo-rescue technique

Abstract

The investigation includes the analysis of genome sizes of 11 Cucurbita species (some represented by several botanical varieties). In the majority of species, the genome size was measured for the first time. Values obtained by flow cytometry were based on propidium iodide (PI) staining technique. In contrast to the uniform chromosome number, the genome size differences within this genus appeared to be large, 2C values ranging from 0.686 pg in C. foetidissima to 0.933 in C. ficifolia. PI determined genome sizes of five cultivated species were 0.864 pg ( C. pepo) , 0.887 pg ( C. maxima) , 0.933 pg ( C. ficifolia) , 0.708 pg ( C. moschata) and 0.748 pg ( C. argyrosperma). The investigation also included several interspecific crosses among cultivated species, using embryo rescue technique. F 1 hybrid plants were obtained from crosses: C. maxima× C. pepo (and vice versa), C. pepo× C. moschata, C. ficifolia× C. maxima, (C. maxima×C. moschata)× C. pepo, C. argyrosperma× C. moschata (and vice versa). The formation of plantlets in the last combination, where C. moschata was used as the female parent, had not been previously reported. The interspecific origin of regenerants was confirmed by evaluating relative nuclear DNA content, estimated by DAPI staining. In all hybrid combinations, the relative nuclear DNA contents in interspecific hybrids was intermediate and differed significantly from those determined in parental species. The results show that differences in genome size within the genus Cucurbita are big enough to be used efficiently in determination of interspecific hybrids.