Development of Advanced Interspecific-bridge Lines among Cucurbita pepo, C. maxima, and C. moschata

Abstract

<jats:p>Interspecific hybridization among the three most economically important cultivated species of Cucurbita spp., <jats:italic>Cucurbita pepo</jats:italic>, <jats:italic>C. moschata,</jats:italic> and <jats:italic>C. maxima</jats:italic> can be made but not readily. By means of various pollination measures, different mating systems, and varying selection methods, nine advanced interspecific-bridge lines were developed, in which the crossing barrier among the species and the male sterility of the F<jats:sub>1</jats:sub> and subsequent generations were overcome over a 12-year period from 1999 through 2011. Despite the considerable influence of parental cultigens and environmental factors on the incompatibility of interspecific crosses, the plant and population compatibility significantly increased when a backcross with a recurrent parent in the same species or a multiple-way cross with a parent in the different species was made. As the generations advanced, the percentage of fertile seeds (PFS) significantly increased in all the sib- and self-families. The four advanced interspecific-bridge lines out of nine not only have gained the normal crossability of interspecific hybridization, but also could eliminate the sexual obstacles of the subsequent generations. The results demonstrate that a two- or three-species bridge line with crossing compatibility can be created by two- or three-species recombination and continuous selection. More importantly, the breakthrough of the advanced interspecific-bridge lines could provide a powerful platform for breeders to transfer favorable traits freely among the species and create more valuable and unique types or varieties through a conventional breeding process.</jats:p>

Interspecific Hybridization between Cucurbita Maxima Duch. and Cucurbita Moschata Duch. for High Efficient Development of Cucurbit Rootstocks

“…Conversely, very low fruit set percentage (33.3%) and fruit set percentage with normal seeds (5.5%) was obtained when C. moschata (Alseiny) was used as male parent and crossed with C. maxima MAX3. Other studies have also succeed to obtain interspecific hybrid plants from the crosses between C. pepo, C. maxima, and C. moschata (Baggett, 1979;Korakot et al, 2010;Karaagac and Balkaya, 2012;Rakha et al 2012;Zhang et al, 2012). Whitaker and Davis (1962) summarized that C. moschata occupies a central position among Cucurbita species and can be crossed with some difficulties with C. pepo, C. maxima, and C. mixta.…”

“…are the most commonly cultivated species of Cucurbita genus which also includes other domesticated species C. argyrosperma Huber, C. ficifolia Bouché, and C. pepo L. A wide genetic diversity have been reported among these species for morphology, disease and insect resistance, and adaptation to abiotic stresses (Whitaker and Bemis 1964;Saade and Hernandez, 1994;Loy, 2004;Hajjar and Hodgkin, 2007). Interspecific hybridization between cucurbit species is an effective way to develop new Cucurbit types and also for crop improvement by transferring important traits such as disease and insect resistance into cultivated crops from their wild relatives (Zhang et al, 2012). However, challenges such as crossing barriers, male sterility, and incompatibility of the interspecific F 1 complicate transfer of useful traits among Cucurbit species (Rhodes 1959;Hiroshi 1963;Shifriss 1987;Zhang et al, 2012).…”

“…Interspecific hybridization between cucurbit species is an effective way to develop new Cucurbit types and also for crop improvement by transferring important traits such as disease and insect resistance into cultivated crops from their wild relatives (Zhang et al, 2012). However, challenges such as crossing barriers, male sterility, and incompatibility of the interspecific F 1 complicate transfer of useful traits among Cucurbit species (Rhodes 1959;Hiroshi 1963;Shifriss 1987;Zhang et al, 2012). Crosses between Cucurbit species were successfully made to obtain fruit and fertile seeds through additional techniques such as embryo rescue, protoplast fusion, mixed pollen pollination, and bud pollination (Hiroshi, 1963;Bemis, 1973;Cheng et al, 2002;Plazas et al, 2016;Rakha et al, 2012).…”

Genomics-based strategies for the use of natural variation in the improvement of crop metabolism

“…Given two candidate incompatible genotypes, for example, a third "bridge" species (compatible to both candidate species) may overcome the fertility barrier and can thus be crossed first to one of the parents; the resulting hybrid may be then crossed to the second species. Bridge and double-bridge crosses have been used widely in breeding of various Solanaceae (especially potato [148]), Brassicacae [149] and Cucurbitaceae [150]. Also, exogenous application of various plant hormones to the flowers, or the use of a mixture of compatible and incompatible pollen on the stigmas, proved successful in increasing pollination and breaking fertilization barriers in Nicotiana spp., wheat, apple, pear and Cucumis spp.…”

Genetic Diversity Among Accessions of Cucurbita pepo Resistant to Phytophthora Crown Rot

“…Currently, there are no commercial C. pepo cultivars immune to P. capsici, but sources of resistance to Phytophthora crown rot have been identified in C. moshata Duchesne (Chavez and Kabelka, 2010) and noncultivated species of squash [C. lundelliana Bailey and C. okeechobeensis (Small) Bailey] (Padley et al, 2009). However, transfer of this resistance into C. pepo is difficult because of wide genetic distances between the species that require resource-intensive techniques, such as embryo rescue and bridge crossing (Rakha et al, 2012;Zhang et al, 2012).…”