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Nicole Smith and Prem L. Bhalla

Brassica oleracea is an important vegetable crop, which includes fully cross-fertile cultivars such as broccoli, Brussels sprouts, cabbage, cauliflower, collard, kohlrabi, and kale. F1 hybrids are desirable, as plants grown from hybrid seeds benefit from the heterotic effect of crossing genetically distinct pure lines. But, there is no practical and reliable method to create male sterility for hybrid seed production that is suitable for Brassica vegetables. We have been working to induce nuclear male sterility in cauliflower (Brassica oleracea var. botrytis) by antisense inhibition of Bcp1, a unique anther-specific gene of Brassica. The production of nuclear male-sterile lines will enable male lines with superior agronomic traits to be converted to female parents. Thus, vegetative propagation of parent plants for hybrid seed production by tissue culture is desirable. To achieve this objective, we compared various plant tissues, including stem, petiole, leaf, leaf rib, flower stem, pedicel, flower bud, and petal as explants for tissue culture propagation of an Australian cultivar (B-4) of cauliflower, Brassica oleracea var. botrytis. Four different MS based media containing different amounts of BAP, NAA, GA3, and silver nitrate were used. The cultures were incubated at 25°C with a 16-hr photoperiod. Initial response was visible within 10 days, but percentage callus, root, and shoot formation was scored after 3 weeks of culturing. Of all the explants tested, pedicel explants showed maximum shoot initiation and leaf explant did not respond to regeneration under the conditions tested. The results from these on going experiments will be presented and discussed.

Open access

Chyun-Chien Liang, Tzu-Yao Wei, and Der-Ming Yeh

Neoregelia cultivars have been used in many areas for landscaping and indoors in a variety of creative ways, but scientific reports of their pollination and hybridization are presently limited. Cross-combinations of Neoregelia cultivars were created to define conditions for pollination timing and to evaluate cross-compatibility. Neoregelia cultivars have short-lived flowers. Hybrid seeds were obtained only when cross-pollination was performed before 1200 hr. Results of 19 cross-combinations including six reciprocal crosses revealed that hybrid seeds were obtained in the female parents with a 1.9- to 2.0-cm style length, but not in those with a 2.6- to 3.0-cm style length. The pollen tube penetrated the ovule as early as 1 day after pollination in the compatible cross, whereas swollen pollen tubes were observed at half and two-thirds of the style in the incompatible cross. Removal of 50% of the style length of the female parents could overcome the fertilization barrier for those incompatible crosses and hybrid seeds could be successfully obtained.

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M. Aneja, T.J. Gianfagna, S.A. Garrison, and E.F. Durner

Precocious flowering can be induced in asparagus (Asparagus officinalis L.) seedlings with N-phenylcarbamate herbicides, such as n-propyl N-(3,4-dichlorophenyl) carbamate (NPC); however, only ≈50% of the treated seeds produce flowering plants because these compounds inhibit germination and seedling emergence. We have improved the treatment method by determining the environmental conditions, timing, dose, and duration needed to maximize the percentage of germination, emergence, and flowering. Imbibing seeds in water for 5 days, and then treating germinated seeds with 0.4 mm NPC for 5 days after radicle emergence, with seedling aeration in the light, resulted in the production of flowering seedlings from >90% of the treated seeds. For freshly harvested seeds, in which germination rates are more variable than aged seeds, individual seedlings must be transferred to NPC within 1 day after radicle emergence to produce a high percentage of flowering plants. For seven male asparagus cultivars, chemical induction of flowering in seedlings with NPC produced a sex ratio similar to that of field-grown plants, demonstrating that NPC induces flowering without altering floral differentiation or sex expression. This method can be used for rapidly and accurately identifying the percentage of females in “male” cultivars.

Open access

Michael J. Havey and Sunggil Kim

Hybrid-onion (Allium cepa) seed is produced using systems of cytoplasmic male sterility (CMS) and two different CMS systems have been genetically characterized. S cytoplasm was the first source of onion CMS identified in the 1920s, followed by T cytoplasm that was described in the 1960s. Numerous studies have documented polymorphisms in the organellar DNAs differentiating S and T cytoplasms from the normal male-fertile cytoplasm of onion. There may be additional source(s) of onion CMS that have been described as “T-like” and appear to be more similar to N and T cytoplasms than S cytoplasm. In this study, onion breeding lines from commercial entities were evaluated for molecular markers distinguishing sources of onion CMS. Our results reveal that bona fide T cytoplasm is rarely used commercially to produce hybrid-onion seed, and both S cytoplasm and “T-like” cytoplasm are widely used. We propose that this “T-like” cytoplasm be labeled as “R” cytoplasm because it may have originated from population(s) of ‘Rijnsburger’ onion in the Netherlands. The results of this study also help to clarify inconsistent reports regarding nuclear male-fertility restoration for different sources of onion CMS.

Free access

David A. Dierig, Pernell M. Tomasi, and Dennis T. Ray

Lesquerella fendleri (Gray) Wats. (lesquerella, Brassicaceae), native to the southwestern United States, is a potentially useful industrial oilseed crop. The seed oil contains hydroxy fatty acids, similar to castor (Ricinus communis L.) seed oil. The unique properties of the oil, along with coproducts, allow additional applications that would not compete with castor oil. Plants with vestigial anthers (male-sterile) were discovered in a greenhouse-grown, nonselected population in 1993. The inheritance of the trait was investigated through four crop seasons. Crosses were made among male-sterile and male-fertile plants from an open pollinated population, thus, they were heterozygous for many traits. Statistical analysis indicated that male sterility is expressed as a result of two nonlinked nuclear genes with epistatic relations and different cytoplasms, which cause partial or total fertility restoration. These ratios fit a 13:3 epistatic ratio, indicating that male sterility is controlled by homozygous recessive alleles at one locus in combination with at least one dominant allele at the second locus, i.e., ms1ms1 Ms2_. Some cross results were skewed in favor of fertile phenotypes presumably due to cytoplasmic effects causing partial fertility restoration. Male-sterile lines could be used for hybrid development and this information will be helpful in implementing a strategy for hybrid development. Hybrid plants and higher yields will enhance the potential for commercialization of this new alternative crop.

Free access

Jane Kahia, Margaret Kirika, Hudson Lubabali, and Sinclair Mantell

importantly it offers potential environmentally friendly approach to the long-term control of coffee diseases and in production of organically grown coffee. The propagation of Ruiru 11 is by F 1 hybrid seed, production through hand artificial cross

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Edward C. Tigchelaar

The coupling phase linkages have been synthesized between the gene aw (without anthocyanin) and the male sterile gene ms15 (and its alleles ms26, ms47, and an Israeli source of male sterility). Less than 2 map units separate aw and ms15 on chromosome 2, providing a convenient seedling marker gene to rapidly identify male sterility for both inbred development and hybrid seed production. The seedling marker also provides a convenient marker to rapidly assess hybrid seed purity. Unique features of each of the alleles involved in male sterility and their use in inbred and hybrid development will be described.

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Michael E. Compton, D.J. Gray, and G.W. Elmstrom

Tetraploid individuals were identified among plants regenerated from cotyledons of diploid watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] cultured in vitro. Tetraploid and diploid plants were distinguished by counting the number of chloroplast per guard cell pair. The mean number of chloroplasts was 19 and 11 for tetraploid and diploid plants, respectively. Self-fertile tetraploids were obtained from the diploid cultivars Mickylee, Jubilee II and Royal Sweet. `Dixielee' and `Minilee' tetraploids failed to set fruit. Progeny obtained from self-fertile tetraploids were crossed with diploid pollinators to produce triploid hybrid seed. All triploid plants produced seedless fruit that was superior or equal to fruit produced by currently available triploid hybrids. This demonstrates that tissue culture can be used to produce high quality tetraploid plants for use in triploid hybrid seed production.

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Soon O. Park, Kevin M. Crosby, Rongfeng Huang, and T. Erik Mirkov

Male sterility is an important trait of melon in F1 hybrid seed production. Molecular markers linked to a male-sterile gene would be useful in transferring male sterility into fertile melon cultivars and breeding lines. However, markers linked to the ms-3 gene for male sterility present in melon have not been reported. Our objectives were to identify randomly amplified polymorphic DNA (RAPD) markers linked to the ms-3 gene controlling male sterility using bulked segregant analysis in an F2 population from the melon cross of line ms-3 (male-sterile) × `TAM Dulce' (male-fertile), convert the most tightly linked RAPD marker to the ms-3 gene into a sequence characterized amplified region (SCAR) marker based on a specific forward and reverse 20-mer primer pair, and confirm the linkage of the RAPD and SCAR markers with the ms-3 gene in an F2 population from the cross of line ms-3 × `Mission' (male-fertile). A single recessive gene controlling male sterility was found in F2 individuals and confirmed in F3 families. Two RAPD markers that displayed an amplified DNA fragment in the male-sterile bulk were detected to be linked to the ms-3 gene in the F2 population from the cross of line ms-3 × `TAM Dulce'. RAPD marker OAM08.650 was closely linked to the ms-3 gene at 2.1 cM. SCAR marker SOAM08.644 was developed on the basis of the specific primer pair designed from the sequence of the RAPD marker OAM08.650. The linked RAPD and SCAR markers were confirmed in the F2 population from the cross of line ms-3 × `Mission' to be consistently linked to the ms-3 gene at 5.2 cM. These markers were also present in 22 heterozygous fertile F1 plants having the ms-3 gene. The RAPD and SCAR markers linked to the ms-3 gene identified, and confirmed here could be utilized for backcrossing of male sterility into elite melon cultivars and lines for use as parents for F1 hybrid seed production.

Free access

X.P. Zhang, B.B. Rhodes, W.V. Baird, H.T. Skorupska, and W.C. Bridges

Hybrid seed production can be facilitated by using male sterility coupled with a seedling marker. This research was initiated to combine the ms male sterility and dg delayed-green seedling marker into watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] lines. Male-sterile plants of the male-sterile line G17AB were crossed with plants of delayed-green breeding line Pale90, which has yellow cotyledons and pale-green, newly developed, true leaves. The double-recessive recombinants, male sterile and delayed green, from the F2 population were backcrossed to the male-fertile plants of G17AB. The pedigree method was used for selection in the progenies. The segregation ratios obtained from F2 and BC1F2 populations suggest that the male-sterile and delayed-green traits are inherited independently and that delayed green is inherited as a single recessive nuclear gene. Two male-sterile watermelon lines with delayed-green seedling marker have been developed. These lines will provide a convenient way to introduce male sterility and the delayed-green seedling marker into various genetic backgrounds. These two lines can be used for testing the efficiency of a new, hybrid, watermelon, seed production system.