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Elisabet Claveria, Jordi Garcia-Mas, and Ramon Dolcet-Sanjuan

Homozygous doubled haploid lines (DHLs) from new cucumber (Cucumis sativus L.) accessions could be useful to accelerate breeding for resistant varieties. DHLs have been generated by in vitro rescue of in vivo induced parthenogenic embryos. The protocol developed involves the following: 1) induction of parthenogenic embryos by pollinating with pollen irradiated with a Co60 γ-ray source at 500 Gy; 2) in vitro rescue of putative parthenogenic embryos identified by their morphology and localized using a dissecting scope or X-ray radiography; 3) discrimination of undesirable zygotic individuals from the homozygous plants using cucumber and melon SSR markers; 4) determination of ploidy level from homozygous plants by flow cytometry; 5) in vitro chromosome doubling of haploids; and 6) acclimation and selfing of selected lines. Codominant markers and flow cytometry confirmed the gametophytic origin of plants regenerated by parthenogenesis, since all homozygous lines were haploids. No spontaneous doubled haploid plants were rescued. Chromosome doubling of haploid plants was accomplished by an in vitro treatment with 500 μm colchicine. Rescue of diploid or chimeric plants was shown by flow cytometry, prior to their acclimation and planting in the greenhouse. Selfing of colchicine-treated haploid plants allowed for the perpetuation by seed of homozygous lines. The high rate of seed set, 90% of the lines produced seed, facilitated the recovery of inbred lines. Despite some limiting factors, parthenogenesis is routinely used in a cucumber-breeding program to achieve complete homozygosity in one generation. Breeding for new commercial hybrid cultivars will be accelerated. DHLs are ideal resources for genomic analyses.

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Maria Jose Gonzalo, Elisabet Claveria, Antonio J. Monforte, and Ramon Dolcet-Sanjuan

hybrid production. This process can be shortened by the generation of inbred lines from doubled haploid (DH) plants. Because the complete genome of DH plants is in a homozygous state, no heterozygous genomic regions are found, and completely homozygous

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Mohammed Elsayed El-Mahrouk, Mossad K. Maamoun, Antar Nasr EL-Banna, Soliman A. Omran, Yaser Hassan Dewir, and Salah El-Hendawy

lines can be obtained by the resulting haploid plant. Haploid, a plant that has a basic chromosome number [gametic chromosome number of diploid plant ( n )], represents a good method to accelerate plant breeding. Consequently, the importance of haploids

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Mohammad Sadat Hosseini Grouh, Kourosh Vahdati, Mahmoud Lotfi, Darab Hassani, and Nejat Pirvali Biranvand

crossing and selection) is time-consuming and limited by available space for field experiments. Biotechnological techniques such as production of haploids offer new opportunities for genetic research in breeding programs ( Höfer and Grafe, 2003 ). Haploids

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Ralph Scorza and Margaret Pooler

We gratefully acknowledge the work of T. Toyama in developing the haploid and doubled haploid lines and providing these lines for use in this study. We thank M. Demuth for assistance in data collection and analysis, M. Brown for consultation

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Kristina Košmrlj, Jana Murovec, and Borut Bohanec

modern cultivars with outstanding characteristics such as high yield, disease resistance, bush growth habit, and uniformity. The most recently released cultivars are hybrids, so the development of an efficient haploid induction protocol for creating

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Davut Keleş, Ceren Özcan, Hasan Pınar, Atilla Ata, Nihal Denli, Namık Kemal Yücel, Hatıra Taşkın, and Saadet Büyükalaca

, haploidization offers a great advantage by shortening the breeding cycle. Haploid plants can be obtained using various tissue culture techniques and full homozygosity can be achieved in quite a short time using these methods. Since the heterozygosity rate is high

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Davut Keleş, Hasan Pınar, Atilla Ata, Hatıra Taşkın, Serhat Yıldız, and Saadet Büyükalaca

of pepper production. The most significant way to increase yield per unit area is to develop cultivars that are resistant to such problems. Haploid plant production methods accelerate plant breeding studies and thus, play an important role in

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Marijana Jakše, Pablo Hirschegger, Borut Bohanec, and Michael J. Havey

Haploid induction via unpollinated flowers or ovaries in onion has been practiced for 20 years, since the discovery that haploid plants can be obtained via gynogenesis ( Muren, 1989 ). Following this major breakthrough, much effort has been made

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Peter T. Hyde, Elizabeth D. Earle, and Martha A. Mutschler

inbred lines ( Bong and Swaminathan, 1995 ; Maluszynski et al., 2003 ; Röber et al., 2005 ). DH plants can be produced in vitro by generating plantlets from gynogenic or androgenic haploid cells. These haploid plantlets either spontaneously double their