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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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G. A. Moore and R. E. Litz

Abstract

Isozyme markers for glutamate oxaloacetate transaminase (GOT), superoxide dismutase (SOD), peroxidase (PER), and malate dehydrogenase (MDH) were identified for Carica papaya L. and the related but sexually incompatible C. cauliflora Jacq. These markers were used to determine the nature of somatic embryos derived from papaya ovules cultured on modified Murashige and Skoog (MS) medium 65 days after controlled pollination with C. cauliflora. Zymograms of plantlets from somatic embryos contained bands specific to either C. papaya or C. cauliflora (PER, GOT) and a unique band not present in the zymogram of either species (PER). Zymograms of somatic embryo-derived plantlets were distinctively different from those of either of the Carica species for all the enzyme systems examined. Evidence from isozyme markers indicates that somatic embryos produced from cultured papaya ovules following pollination with C. cauliflora may be hybrids. The isozyme banding patterns of 60 plantlets derived from somatic embryos from the same ovule were very uniform and suggest genetic uniformity among the regenerated plantlets.

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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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Richard M. Manshardt and Timothy F. Wenslaff

Abstract

A study of reproductive barriers limiting interspecific hybridization between Carica papaya L. and C. cauliflora Jacq. was undertaken in four reciprocal interspecific crosses using two different lines of each species. Particular attention was focused on determining whether polyembryonic clusters produced in these crosses were of maternal or zygotic origin. Prezygotic barriers were unimportant; pollen tube penetration and zygote formation were similar in intra- and interspecific crosses. Substantial postzygotic disruptions were observed, including disorganized growth and abortion of hybrid embryos and lack of normal endosperm development. In most crosses, disorganized embryos aborted before differentiating into polyembryonic structures. However, crosses employing UH345 (C. cauliflora) as female parent produced some embryos that developed to maturity (6 months), and, in these crosses, embryogenic proliferation from zygotic tissue became evident as early as the beginning of the 3rd month. There was no evidence of somatic embryogenesis from maternal tissues in any cross. Embryos rescued 3 to 6 months after pollination continued embryogenic growth in vitro on basal Murashige and Skoog (MS) medium and germinated on medium containing 0.2 mg BA/liter and 0.5 mg NAA/liter. Zymograms assayed for isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase activity confirmed the zygotic origin of tissues taken from in vitro cultures and recovered plantlets. Vigor, viability, and fertility (< 1% stainable pollen) of hybrids recovered from embryo culture were low. Chemical names used: 6-benzylaminopurine (BA); 1-napthaleneacetic 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