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Dianiris Luciano-Rosario, Luis A. Cruz-Saavedra and Dimuth Siritunga

-Bonilla et al., 2014 ; Wendel et al., 1992 ). Papaya is a tropical fruit crop belonging to the Caricaceae family. It is thought to be native to Central America and is cultivated in most of the world’s tropical areas ( Arumuganathan and Earle, 1991 ; Food

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Jenjira Chumpookam, Huey-Ling Lin and Ching-Chang Shiesh

from a wide variety of biotic sources, including wood, straw, mixtures of dry and fresh plant material, and charred wood, can stimulate germination ( Brown and Van Staden, 1997 ). Papaya ( Carica papaya ) seed germination is affected by many

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Juan Carlos Álvarez-Hernández, Javier Zaragoza Castellanos-Ramos and Cesar Leobardo Aguirre-Mancilla

In Mexico, Carica papaya L. is cultivated in 19 states, with a harvested area of 16,684 ha, concentrated mainly in Veracruz (3196 ha), Colima (2850 ha), Oaxaca (2702 ha), Michoacan (2368 ha), and Guerrero (1124 ha) ( SIAP-SAGARPA, 2017 ). Despite

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B. Castillo, M.A.L. Smith, D.L. Madhavi and U.L. Yadava

Interactions between irradiance levels (5–40 μmol·m-2·s-1) and iron chelate sources (FeEDTA and FeEDDHA) were observed for Carica papaya shoot tip cultures during both the establishment and proliferation stages of microculture. Reduced levels of irradiance (5 μmol·m-2·s-1) favored shoot tip establishment regardless of the source or level of iron. However, the highest percentage of successful explant establishment (100%), and significantly greater leaf length (1.16 cm; over double the size attained in any other treatment), resulted when a low concentration of FeEDTA alone was used at low irradiance. During the subsequent shoot proliferation stage, however, higher irradiance levels (30 and 40 μmol·m-2·s-1) were required, and FeEDTA failed to support culture growth when used as the sole iron source. The highest multiplication rates (3.6 shoots per explant) and leaf chlorophyll concentrations (0.22 mg/g fresh mass), and significantly improved shoot quality were achieved at 30 μmol·m-2·s-1 irradiance when both iron chelate formulations were combined (each at a 100 μM concentration) in the proliferation medium. Chemical names used: benzylamino purine (BA); ferric disodium ethylenediamine tetraacetate or FeNa2EDTA (FeEDTA); ferric monosodium ethylenediamine di(o-hydroxyphenylacetate), (FeNaEDDHA) or Sequestrene 138Fe (FeEDDHA); indoleacetic acid (IAA); 1-naphthaleneacetic acid (NAA).

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Manoel T. Souza Jr., Paula F. Tennant and Dennis Gonsalves

Line 63-1 is a `Sunset'-derived transgenic papaya expressing the coat protein (CP) gene from a mild mutant of a Hawaiian isolate of Papaya ringspot virus (PRSV). Previous work showed that line 63-1 R1 plants exhibited a range of resistance to severe PRSV isolates from Hawaii (HA), Jamaica (JA), Thailand (TH), and Brazil (BR). Genetic and molecular data obtained in this study confirm that line 63-1 has two CP transgene insertion sites; segregation analysis shows that the CP and the npt II genes are present at both loci. To study the potential effect of gene dosage on resistance, various populations of R1, R2, and R3 seedlings were challenged by PRSV HA, BR, and TH. A R1 population obtained by self-pollination of line 63-1 hermaphrodite R0 plant exhibited resistance to all three isolates. The percentage of plants resistant to all three PRSV isolates increased in 63-1-derived populations as a result of recurrent selection. Additional genetic studies demonstrate that the number of resistant plants in a 63-1-derived population is directly correlated with the number of plants with multiple transgene copies. We conclude that transgene dosage plays a major role in affecting the resistance of 63-1 to PRSV isolates from various geographical locations.

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Richard Manshardt

The papaya ( Carica papaya ) is a member of the Caricaceae, which consists of five New World genera and one African genus. In 2000, the genus Carica was split to better reflect molecular and morphological differences between a group of ≈21

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S. Lius, R. Manshardt, D. Gonsalves, M. Fitch, J. Slightom and J. Sanford

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

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Claudinei Andreoli and Anwar A. Khan

Products Corp., Denver, for MicroCel E; Imperial Chemical Industries for gibberellin (GA 4+7 ); and the Known-You Seed Co., Kaohsiung, Taiwan, for papaya seeds. The cost of publishing this paper was defrayed in part by the payment of page charges. Under

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Cristina Zambrana-Echevarría, Lorriane De Jesús-Kim, Rocio Márquez-Karry, Dimuth Siritunga and David Jenkins

PRSV is the most serious, widespread, and damaging virus affecting papaya ( Carica papaya L.) worldwide ( Gonsalves, 1998 ; Teixeira da Silva et al., 2007 ). The PRSV belongs to the species-rich genus Potyvirus in Potyviridae and has a

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Huey-Ling Lin, Jenjira Chumpookam, Ching-Chang Shiesh and Wen-Hsin Chung

Papaya is one of the most important tropical fruit crops with annual production of ≈9.1 million tones and economic value of U.S. ≈$6097 million ( FAOSTAT, 2012 ). Damping-off is a major disease of papaya ( Carica papaya L.) seedling in nurseries