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nucellar or zygotic origin, although most citrus genotypes produce nucellar seeds at a very high rate. In conclusion, we have successfully used protoplast fusion to produce several new allo- and autotetraploids that can be used as breeding parents in future

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Citrus: Genetics, Breeding and Biotechnology . Iqrar Ahmad Khan (editor). 2007. CABI, CABI North American Office, 875 Massachusetts Ave., 7th Floor, Cambridge, MA 02139, www.cabi.org . 370 p., incl. index. $160.00, hardback, ISBN 9780851990194

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interploid crosses for triploid production ( Grosser and Gmitter, 2009 ). In fact, citrus somatic hybridization has proven to be a key tool to generate allotetraploid breeding parents for use in interploid crosses to generate seedless triploids for mandarin

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one-fourth of that in 1975. To maintain and develop the citrus industry in Japan, it is indispensable to develop new mandarin cultivars with large fruits and high sugar content in addition to ease of eating. The citrus breeding program in Japan began

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flavor. A citrus cross-breeding program was begun in 1937 at the then National Horticulture Research Station of the Ministry of Agriculture and Forestry [now Okitsu Citrus Research Station of the National Agriculture and Food Research Organization

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175 ORAL SESSION 51 (Abstr. 360-366) Rose and Tree Fruits (Citrus and Papaya): Breeding and Genetics

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Citrus rootstocks resistant to decline induced by citrus tristeza (CTV) have been developed using resistance found in Poncirus trifoliata (L.) Raf. A breeding line with resistance to CTV infection, US119 [Citrus paradisi Macf. cv. Duncan × P. trifoliata (L.) Raf. × C. sinensis cv. Succory], was developed and crossed with `Ambersweet' orange [C. reticulata Blanco × (C. paradisi × C. reticulata) × C. sinensis] to develop scions resistant to CTV infection. Fifty-one progeny were tested for CTV resistance by grafting each to rough lemon [C. limon (L.) Burm. f.] seedlings infected with CTV. These propagations were assayed repeatedly by ELISA. Seventeen progeny consistently tested negative for CTV (resistant), 24 were consistently positive (susceptible), and 10 gave weak or inconsistent reactions. These results confirm the feasibility of developing CTV-resistant scions by use of US119 to solve the stem pitting disease caused by CTV.

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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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‘Minnie Finger Lime’ is a new citrus cultivar released 15 Feb. 2018 ( Bowman, 2018 ) by the Agricultural Research Service (ARS) of the U.S. Department of Agriculture (USDA). The major positive attributes of this new citrus scion are the combination

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Abstract

Nearly all commercial citrus trees are grafted, and the rootstock has a major effect on the performance of the scion cultivar. A citrus tree’s resistance to or tolerance of disease, nematodes, salt, cold, and other factors may be influenced by the rootstock. Also, the rootstock affects the tree’s adaptability to various environmental factors, as well as the quantity and quality of fruit that it produces. No available rootstock possesses all of the desirable traits needed by the citrus industry. Also, changes in culture and production problems create new demands.

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