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Maureen M.M. Fitch, Paul H. Moore, Terryl C.W. Leong, Leslie Ann Y. Akashi, Aileen K.F. Yeh, Susan A. White, Amy S. Dela Cruz, Lance T. Santo, Stephen A. Ferreira and Leslie J. Poland

Papaya seedlings segregate for sex expression as females or hermaphrodites. Typically only hermaphrodite fruit are marketed in Hawaii. The agronomic practice of growing multiple seedlings that are later thinned to a single hermaphrodite tree is wasteful of seed, labor, and resources, especially when seed is costly. We compared growth of plants propagated by the clonal methods of micropropagation or rooting vegetative cuttings versus plants initiated as seedlings and transplanted. The seedlings were either single-planted hermaphrodites as identified by the polymerase chain reaction (PCR) or multiple-planted, thinned seedlings. The experiments were carried out in three different locations on two islands in Hawaii. Clonally propagated plants were significantly shorter than seedlings and bore flowers earlier and lower on the trunk at all locations. Stem diameter differences were not significant even though plant size was different at planting time. Percentage of trees in bud varied significantly in the third month after transplanting when about 90% of the rooted cuttings and large micropropagated plants had formed flower buds while only one multiple-planted seedling developed a bud. Overall, the clonally propagated plants were more vigorous and earlier bearing than were the seedling plants. There is good potential for adoption of clonal propagation when production becomes efficient enough to compete in price with the current practice of over planting and thinning.

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Maureen M.M. Fitch, Paul H. Moore, Terryl C.W. Leong, Leslie Ann Y. Akashi, Aileen K.F. Yeh, Susan A. White, Amy S. Dela Cruz, Lance T. Santo, Stephen A. Ferreira and Leslie J. Poland

Gynodioecious papaya (Carica papaya L.) seedlings in commercial cropping systems in Hawaii are typically multiple-planted and thinned upon flowering to a single hermaphrodite because seedlings segregate for sex expression. Use of clonally propagated hermaphrodites would eliminate the over-planting practice and may provide other advantages. Yields of clonally propagated hermaphrodites were compared with single- and multiple-planted seedlings in three fields on two islands in Hawaii. Cloned hermaphrodites were either rooted cuttings or in vitro micropropagated plants. Clonally propagated plants bore ripe fruit 1 to 3 months earlier than thinned seedlings and had significantly higher early and cumulative yields. At each site, cumulative yields of thinned seedlings never reached the same level as those of clonally propagated plants. The yield benefit from clonally propagated plants was greatest at Keaau, the lowest sunlight and least productive test site.

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Richard M. Manshardt, Cathy Mello, Sharon D. Lum and Leanne Ta

Genetically engineered (GE), virus-resistant papaya cultivars in Hawaii are easily identified by a colorimetric assay for the β-glucuronidase (GUS) marker transgene. We used GUS to track pollen movement from a central 1-acre plot of gynodioecious GE `Rainbow' plants into seeds on surrounding border rows of non-GE `Sunrise' papaya. GUS evidence of cross-pollination occurred in 70% of female plants (43% of assayed seeds), compared with only 13% of the predominantly self-pollinating hermaphrodite plants (7% of seeds) segregating in the gynodioecious `Sunrise' border rows. The percentage of GUS+ seeds in border row plants showed a weak negative correlation (r = –0.32) with distance from the nearest GE tree (30 m maximum). In a non-GE papaya field located less than a mile downwind from the `Rainbow' source, no evidence of GUS was found in 1000 assayed seeds. In a separate study, the origin of GUS+ seed discovered in papaya fruits from an organic farm was investigated. Leaf GUS assays revealed that 70% of trees were GE, indicating that the grower had planted GE seed. The impact of pollen drift from GE trees in the same field was determined by screening seed samples from 20 non-GE hermaphrodites for GUS expression. Only three hermaphrodites (15%) showed GUS+ seeds, at low levels ranging from 3% to 6% of contaminated samples. These data indicate that the major source of GE contamination in organic fields is seeds of unverified origin, rather than pollen drift from neighboring GE fields. Organic growers are advised to: 1) plant only seed that is known to be non-GE, preferably obtained by manual self-pollination of selected non-GE hermaphrodites; 2) avoid open-pollinated seed; and 3) grow only hermaphrodite (self-pollinating) trees, removing any female or male plants from production fields.

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Tracie K. Matsumoto, Francis T.P. Zee, Jon Y. Suzuki, Savarni Tripathi, James Carr and Bruce Mackey

.M. Gonsalves, D. Slightom, J.L. Sanford, J.C. 1992 Virus resistant papaya plants derived from tissues bombarded with the coat protein gene of papaya ringspot virus BioTechnology 10 1466 1472 Freese, L

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Kelly A. Zarka, Ria Greyling, Inge Gazendam, Dean Olefse, Kimberly Felcher, Gurling Bothma, Johan Brink, Hector Quemada and David S. Douches

Commission ( BASF, 2010 ). Golden rice ( Oryza sativa ) is another example; however, it has not yet been released ( Golden Rice Humanitarian Board, 2009 ). Currently, the only example of a publicly released GM crop is papaya ringspot virus-resistant papaya

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Richard Manshardt

, D. 2002 Virus coat protein transgenic papaya provides practical control of Papaya ringspot virus in Hawai’i Plant Dis. 86 101 105 Fitch, M. Manshardt, R. Gonsalves, D. Slightom, J. Sanford, J. 1992 Virus resistant papaya plants derived from tissues

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Jean-Michel Hily, Michel Ravelonandro, Vern Damsteegt, Carole Bassett, Cesar Petri, Zongrang Liu and Ralph Scorza

806 811 Fitch, M.M.M. Manshardt, R.M. Gonzalves, D. Slightom, J.L. Sanford, J.C. 1992 Virus resistant papaya plants derived from tissues bombarded with the coat protein gene of papaya ringspot