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Zenaida Viloria and Jude W. Grosser

Interploid hybridization was conducted using `Key' lime [Citrus aurantifolia (Cristm.) Swing.], `Lakeland' limequat hybrid [C. aurantifolia × Fortunella japonica (Thumb.) Swing.], Palestine sweet lime (C. limettioides Tan.), `Etrog' citron (C. medica L.), and seven lemon [C. limon (L.) Burm. F.] varieties as female progenitors and five allotetraploid somatic hybrids {`Hamlin' sweet orange [C. sinensis (L.) Osbeck] × `Femminello' lemon (C. limon)]; `Key' lime × `Valencia' sweet orange (C. sinensis); `Valencia' sweet orange × rough lemon (C. jambhiri Lush); Milam lemon (purported C. jambhiri hybrid) × `Femminello' lemon (C. limon); and `Valencia' sweet orange × `Femminello' lemon} and two autotetraploids [`Giant Key' lime (C. aurantifolia) and `Femminello' lemon] as pollen progenitors. A few tetraploid × diploid crosses were also performed. Thirty-five parental cross combinations were accomplished in 2000, 2001, and 2002. The breeding targets were seedlessness, cold-tolerance, and disease resistance. Triploid hybrids were recovered through embryo culture. Generation of triploid citrus hybrids was affected by several factors including sexual compatibility, cross direction, embryo developmental stage, pollen viability, as well as horticultural practices and climatic conditions. Efficiency of triploid hybrid production was higher in diploid × tetraploid crosses than the reciprocal. Many more triploid hybrids were generated from lemon seed progenitors compared to the other acid citrus fruit progenitors. `Todo el Año', `Lisbon', and `Limonero Fino 49' showed the highest sexual compatibility. Embryo germination rate and normal plant recovery were also higher in lemons as compared to the other seed progenitors. Low winter temperatures might have affected the hybrid production efficiency from tropical acid fruit progenitors. A total of 650 hybrids (mostly triploid) were transferred to soil. The novel genetic combinations of these progenies should be valuable for the genetic improvement of acid citrus fruit (lemons and limes).

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Darren Touchell, Zenaida Viloria and Thomas Ranney

Weigela Thunb. consists of 12 species distributed throughout Northeast Asia. Diervilla Mill. is a closely related genus containing three species endemic to North America. Taxa from both of these genera are important nursery crops. Hybrids between these genera could potentially combine the excellent cold hardiness and adaptability of Diervilla with diverse forms, foliage colors, and flower colors found in Weigela. Prior attempts to create intergeneric hybrids between these genera were unsuccessful and resulted in embryo abortion before seeds matured. To overcome this barrier, ovule culture and micropropagation procedures were used to develop intergeneric hybrids. Cleaved amplified polymorphic sequences (CAPS) analysis was used to verify hybrids. Intergeneric crosses, D. lonicera × W. middendorfiana, D. sessilifolia × W. florida (two clones), and D. lonicera × W. florida were attempted. Crosses of D. lonicera × W. middendorfiana did not produce viable hybrids. From the remaining three crosses, a total of 544 plants were obtained from 1278 ovules. About 85% of the 544 plants appeared very chlorotic or had low vigor, and senesced when transferred to multiplication medium. Only 80 of the 544 plants were successfully maintained in tissue culture, of which 10 have been successfully transferred ex vitro. CAPS analysis indicated that a majority of these plants were hybrids. Further studies are focused on improving tissue culture procedures and other methods to develop tetraploids to increase plantlet vigor and fertility.

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John M. Dole, Zenaida Viloria, Frankie L. Fanelli and William Fonteno

Vase life of ‘Karma Thalia’ dahlia (Dahlia ×hybrida), ‘Lace Violet’ linaria (Linaria maroccana), ‘Sunrise’ lupine (Lupinus hartwegii ssp. cruickshankii), ‘Temptress’ poppy (Papaver nudicaule), ‘Indian Summer’ rudbeckia (Rudbeckia ×hybrida), ‘Jemmy Royal Purple’ trachelium (Trachelium caeruleum), and ‘Benary's Giant Scarlet’ and ‘Sun Gold’ zinnias (Zinnia elegans) was determined after being subjected to postharvest handling procedures. Cut dahlia, lupine, poppy, rudbeckia, trachelium, and ‘Sun Gold’ and ‘Benary's Giant Scarlet’ zinnia flowers could be held in unamended tap or deionized (DI) water with no effect on vase life. Vase life of linaria was longest when placed in DI water with 8-hydroxyquinoline citrate and a solution pH of 3.5. A vase solution of 2% sucrose without foam extended consumer vase lives for linaria, trachelium, and ‘Benary's Giant Scarlet’ zinnia. Floral foam or 2% or 4% sucrose had no effect on the consumer vase life of dahlia, lupine, rudbeckia, and poppy. Trachelium and rudbeckia did not tolerate a 20% sucrose treatment for 24 h, whereas linaria and ‘Benary's Giant Scarlet’ zinnia had a longer vase life with a 10% sucrose pulse than a water-only pulse. For trachelium, the longest (17.5 days) consumer vase life occurred when the Chrysal Professional 2 Processing solution (CP2) was used after pretreatment with DI water. Either of two commercial holding solutions, CP2 or Floralife Professional (FLP), similarly extended the vase life of linaria. The use of FLP or CP2 improved consumer vase life of dahlia, lupine, and poppy compared with DI water. Dahlia, trachelium, and zinnia flowers could not be cold stored at 2 °C. Lupine and poppy could be stored at 2 °C wet or dry for 2 weeks. Linaria and rudbeckia could be cold stored for 3 weeks. Lupine and trachelium were susceptible to 1 μL·L−1 exogenous ethylene, which induced floret abscission in lupine and stopped floret opening in trachelium. 1-Methylcyclopropene and silver thiosulfate similarly suppressed the ethylene effect. Cut linaria, zinnia, dahlia, rudbeckia, and poppy flowers were unaffected by exogenous ethylene.

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Richard T. Olsen, Thomas G. Ranney and Zenaida Viloria

A series of studies were conducted to determine medium components necessary for ovule and embryo culture of ×Chitalpatashkentensis Elias & Wisura hybrids in order to improve recovery of interploid crosses. Ovules were collected at 2, 3, 4, 5, and 6 weeks after pollination (WAP) from selfed tetraploid × Chitalpa (S) and tetraploid × Chitalp × diploid Catalpabignonioides Walt. (3×) hybrids. Excised ovules were placed in petri dishes with Schenk and Hildebrandt (SH) medium and 0.7% agar, with or without coconut-water (2%) and three sucrose concentrations (20, 40, or 80 g·L-1). No ovules germinated for either cross in any treatment at 2, 3, and 4 WAP. Selfed ovules germinated at 5 WAP, in both 20 and 40 g·L-1 sucrose. At 6 WAP, 3× ovules germinated in 20 g·L-1 sucrose. Coconut water provided no apparent benefit. Embryos were apparent at 6 WAP, so a new study was initiated to compare ovule vs. embryo culture at this sample date. Excised embryos germinated in greater percentages than ovules, in all treatment combinations at 6 WAP. Germination in 80 g·L-1 sucrose was observed only for S embryos without coconut water. Greatest 3× germination (16.7%) was observed for embryos in 20 g·L-1 sucrose without coconut water. A final study was conducted to investigate the effect of gibberellic acid (GA3) on embryo germination. Embryos were harvested at 7 WAP for both crosses and grown in SH medium supplemented with 20 g·L-1 sucrose and 0, 1, 2, or 4 μm GA3. The addition of GA3, regardless of concentration, increased germination from 30.6% to 99.1% for S embryos and from 11.1% to 99.1% for 3× embryos.

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Richard T. Olsen, Thomas G. Ranney and Zenaida Viloria

×Chitalpa tashkentensis Elias & Wisura is a sterile intergeneric hybrid [Catalpa bignonioides Walt. × Chilopsis linearis (Cav.) Sweet]. To restore fertility in ×Chitalpa the following were evaluated: 1) oryzalin as a polyploidization agent, 2) fertility of induced polyploids, and 3) in vitro culture methods for embryo rescue of interploid crosses. Meristems of ×Chitalpa `Pink Dawn' were submerged in an aqueous solution of 150 μm oryzalin for 0, 6, 12, or 24 hours and ploidy analyzed via flow cytometry. As treatment duration increased, recovery of diploids decreased as mixoploids and shoot mortality increased. Two tetraploid shoots occurred in the 24-hour treatment. Four tetraploids and two cytochimeras were stabilized in total. Tetraploids flowered sparsely; however, cytochimeras flowered profusely and these were used to study fertility at the tetraploid level. Diploid ×Chitalpa `Pink Dawn' pollen was essentially nonviable, but cytochimera pollen stained and germinated equal to or greater than pollen of C. bignonioides and C. linearis `Bubba'. Cytochimera ×Chitalpa were selfed yielding tetraploid seedlings, crossed with C. bignonioides to yield triploids, but failed in reciprocal crosses with C. linearis `Bubba' and `Burgundy Lace'. To increase recovery of triploids, germination of triploid and tetraploid embryos was investigated, as either intact ovules or excised embryos, on Schenk and Hildebrandt (SH) basal salts supplemented with sucrose at 20, 40, and 80 g·L-1, presence or absence of 2% coconut-water, and gibberellic acid (GA3) at 0, 1, 2, or 4 μm, and harvested weekly beginning 2 weeks after pollination (WAP). Germination of triploids (cytochimera ×Chitalpa × diploid C. bignonioides) and tetraploids (selfed cytochimera ×Chitalpa) were greatest with excised embryos at 7 WAP on SH supplemented with sucrose at 20 g·L-1 and ≥1 μm GA3. Germination of triploids (diploid C. linearis × cytochimera ×Chitalpa) was <5% at 4, 5, or 6 WAP on the same medium as above. Oryzalin effectively induced polyploidy and restored fertility in ×Chitalpa `Pink Dawn'. Successful crosses between hybrid and parental taxa of different ploidy levels, coupled with embryo culture will facilitate a ×Chitalpa breeding program. Chemical names used: 4(dipropylamino)-3,5-dinitrobenzenesulfonamide (oryzalin).

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Kelly M. Oates, Thomas G. Ranney, Darren H. Touchell and Zenaida Viloria