1a. Objectives (from AD-416):
The objectives of this SCA are: 1) to characterize transgenic line 63-1 for its potential as papaya ringspot virus (PRSV) resistant breeding stock, and 2) to characterize hybrids from transgenic SunUp and a nontransgenic Sunrise selection with excellent appearance and shipping quality.
1b. Approach (from AD-416):
Objective 1. Transgenic line 63-1 is resistant to PRSV and has been deregulated in the US. Unlike line 55-1, which is the parent of the commercial Rainbow papaya, line 63-1 has two coat protein gene inserts and shows broad resistance to other strains of PRSV. Evidence from genetic crosses indicates that the two coat protein transgene inserts segregate independently. Line 63-1 will be characterized for its border sequences in order to clearly distinguish the coat protein gene inserts, and will be used as a crossing parent to broaden the resistance of transgenic lines. Objective 2. The relatively short shelf-life and speckled surface of the transgenic SunUp papaya make it difficult for Hawaii to effectively export papaya to the mainland US east coast especially. A nontransgenic Sunrise papaya selection was identified to have good shelf-life and lacked fruit blemishes. The papaya will be crossed to transgenic SunUp papaya and the progenies evaluated for PRSV resistance, good shelf life, and lack of fruit blemishes. Promising progenies will be further crossed and evaluated. Formerly 5320-21000-013-09S (05/13).
3. Progress Report:
The objectives of this cooperative agreement to improve virus resistance, horticulture, and shipping of Hawaiian papaya directly contributes to objective 1 of the inhouse parent project. This is the final report for this project. This has been an extremely productive project in terms of obtaining deregulation of the transgenic “Rainbow” papaya for shipment to Japan. All technical steps and necessary paperwork was also completed for consideration by China for import of “Rainbow.” As previously reported, significant advances were also made in analysis of transgenic papaya line 63-1. Transgenic line 63-1 is resistant to papaya ringspot virus (PRSV) and was deregulated by the Animal and Plant Health Inspection Service (APHIS) and the Environmental Protection Agency (EPA), but was not further pursued for commercialization because it had large segments of vector sequences. However, it has two coat protein transgenes and thus is an attractive model for basic studies to explore the impact that these coat protein transgenes would have on resistance to papaya ringspot virus. Border sequences were obtained and deep sequencing of the transgenic papaya genome is progressing. A further objective of this project was to develop transgenic papaya with less fruit blemishes. Fruits of the blemish free papaya (presumably ‘Golden Sunrise’) were obtained from a market in California and seeds of the fruit were grown on the Hamakua coast of Hawaii; this line was designated N08-75. Fruit from those plants showed similar characteristics to the commercial variety and indeed were blemish free. The trees were self pollinated and harvested seeds were also grown in the Waiakea region of the Hawaii island that resemble the ‘lava’ type of soil and moisture conditions of Puna, where 90 percent of Hawaii’s papaya are grown. The resulting fruit of these trees were also free of freckles. To incorporate PRSV-resistance to the line, the freckle free line was crossed with ‘SunUp’, which is a PRSV-resistant transgenic cultivar that was derived by transforming a nontransgenic ‘Sunset’, a sibling line to ‘Sunrise’. Recipricol crosses were made using ‘SunUp’ and N08-75 and seeds of the cross have been planted out in Waiakea and also in Puna at a commercial papaya farm. In the current year, protocols were developed to evaluate the impact of post-harvest handling on quality of the fruit, when it is ready for harvest.