Progress 10/01/98 to 09/30/04

Outputs
Work toward the development of a large fruited high quality transgenic papaya with resistance to papaya ringspot virus made great advances. Papaya ringspot virus resistance has been obtained in transgenic papaya containing the coat protein of the local strain of PRV. Transgenic R1 lines were grown out and selections were made for virus tolerance, fruit production and quality. The lines segregated out to produce susceptible plants within a line. Resistant lines sustained resistance after being inoculated twice with papaya ringspot virus. Selections were made to develop homozygous lines for virus resistance. Inbreeding of virus resistant lines was conducted to develop homozygous papaya lines with virus resistance. All plants were hand inoculated with the virus twice starting when the plants reached one meter. This method of hand inoculation has potential to spread bacterial and other viral diseases from the source plants to the new papaya field. Virus resistant transgenic R2 lines were selected and the plant and fruit quality recorded. Flowers were self pollinated to obtain the next generation seeds. Due to the time and effort required to hand inoculate the plants, a system was used to apply Kanamycin in combination with DMSO to young seedlings. The transgenic lines were developed and selected for Kanamycin resistance originally in vitro. Through this method, segregating heterozygous and uniform homozygous papaya lines were elucidated and selected prior to planting in the field. Susceptible nontransgenic papaya seedlings incur yellow spots from the kanamycin spray. Susceptible seedlings are visually recognized and rouged from the seedling trays. Transgenic homozygous lines can be easily recognized from the heterozygous segregating seed lines. Through controlled pollinations, the virus resistant transgenic homozygous papaya lines can be maintained.

Impacts
Workshops on papaya production were conducted that attracted over 30 local farmers. Tours of the transgenic papaya field plots by local farmers and back yard gardeners have produced favorable responses. The tour groups could easily distinguish the healthy transgenic papaya plants from the virus-infected plants. They were encouraged by the technology and could see first hand that the transgenic plants grow normally as a papaya and isn't some freaky plant in appearance. All growers were eager to try the transgenic lines when the seeds are approved for release. By providing tours of the transgenic field plots to the local residents, they become educated on what genetically modified plants are and their impact in their lives. Farmers and backyard gardeners have used the colorful picture oriented fact sheet to identify and remove male trees at the flower bud stage of development,within three feet off the ground, saving them resources and time. Development of a system to screen transgenic papaya seedlings reduces the cost to farmers and increases the efficiency for obtaining stable virus resistant papaya.

Publications

• Zimmerman, T.W., J. Richards and I. James. 2003. Papaya somatic embryogenesis. UVI Food & Agriculture Research 8:12-13.
• Zimmerman, T.W. 2003. Determining the sex of papaya plants for successful management of backyard and commercial production. UVI-AES Factsheet 4p.
• Zimmerman, T.W. 2000. Papaya trees selected for the U.S. Virgin Islands. International Society for Tropical Horticulture. 44:36-38.
• Zimmerman,T.W. and J.A. Kowalski. 2001. Selection for early bearing papayas in the Virgin Islands. Proc. 37th Caribbean Food Crops Society 349-350.
• St.Brice, N. and T.W. Zimmerman. 2002. Selection of Transgenic Papaya Seedlings utilizing Kanamycin and DMSO. Annual Biomedical Research Conference for Minority Students, November 13-16, New Orleans. Pp.406.

Progress 01/01/03 to 12/31/03

Outputs
Transgenic papaya lines have been developed that contain the Papaya Ringspot Virus coat protein from the local strain of the virus. Breeding and selection has been ongoing to develop inbred lines that are homozygous for the virus resistance to negate the segregation and field selection of the virus susceptible, non-transgenic. A system has been developed to select the transgenic papayas at the seedling stage using a combination of DMSO and kanamycin. Susceptible non-transgenic papaya seedlings incur yellow spots from the kanamycin spray. Susceptible seedlings are visually recognized and rouged from the seedling trays. Transgenic homozygous lines can be easily recognized from the heterozygous, segregating seed lines. Through controlled pollinations, the virus resistant transgenic homozygous papaya lines can be maintained.

Impacts
Farmers and backyard gardeners have used the picture oriented fact sheet to identify and remove male trees at the flower bud stage of development, within three feet of the ground, saving them resources and time.

Publications

• Zimmerman, T.W., J. Richards and I. James. 2003. Papaya somatic embryogenesis. UVI Food & Agriculture Research 8:12-13.
• Zimmerman, T.W. 2003. Determining the sex of papaya plants for successful management of backyard and commercial production. UVI-AES Factsheet 4p.

Progress 01/01/02 to 12/31/02

Outputs
Papaya ringspot virus resistance has been obtained in transgenic papaya containing the coat protein of the local strain of PRV. Inbreeding of virus resistant lines to develop homozygous papaya lines with virus resistance. All plants were hand inoculated with the virus twice starting when the plants reached one meter. This method of hand inoculation has potential to spread bacterial and other viral diseases from the source plants to the new papaya field. Virus resistant transgenic R2 lines were selected and the plant and fruit quality recorded. Flowers were self pollinated to obtain the next generation seeds. Due to the time and effort required to hand inoculate the plant, a system was used to apply Kanamycin in combination with DMSO to young seedlings. The transgenic lines were developed and selected for Kanamycin resistance in vitro. Through this method, segregating heterozygous and uniform homozygous papaya lines were elucidated and selected prior to planting in the field.

Impacts
Development of a system to screen transgenic papaya seedlings will speed the development and increase the efficiency for obtaining stable virus resistant papaya.By providing tours of the transgenic field plots to the local residents, they become educated on what genetically modified plants are.

Publications

• St. Brice, N. and T.W. Zimmerman. 2002. Selection of Transgenic Papaya Seedlings utilizing Kanamycin and DMSO. Annual Biomedical Research Conference for Minority Students, November 13-16, New Orleans. P.406.

Progress 01/01/01 to 12/31/01

Outputs
Work toward the development of a large fruited high quality transgenic papaya with resistance to papaya ringspot virus made great advances during this year. Transgenic R1 lines were grown out and selections were made for virus tolerance, fruit production and quality. The lines segregated out to produce susceptible plants within a line. Resistant lines retained resistance after being inoculated twice with papaya ringspot virus. Selections were made to develop homozygous lines for virus resistance.

Impacts
Farmers and guests from Trinidad touring the transgenic papaya plot were impressed with the viral resistance and the quality of fruit. They were eager for the research to develop to a point when seeds will be released for public use.

Publications

• Zimmerman, TW, JA Kowalski. 2001. Selection for early bearing papayas in the Virgin Islands. Proc. 37th Caribbean Food Crops Society (in press).

Progress 01/01/00 to 12/31/00

Outputs
Breeding and selection has been ongoing to develop papayas with tolerance to papaya ringspot virus and fruit production starting at or less than 70 cm from the ground. This is the first time in six years that a hurricane didn't destroy the crop. This has allowed for production data to be collected for the full fruiting period. Nine varieties have been selected and maintained as breeding lines. Self-pollinations were made on these lines to obtain seeds, which were made available to farmers and backyard growers. F1 hybrid papayas, generated from crosses between the inbred lines the previous year, were grown. Three F1 hybrid combinations have shown potential and were self-pollinated to obtain F2 seeds.

Impacts
A workshop on papaya production was conducted that attracted over 30 local farmers. Seeds were made available to farmers and backyard gardeners from the nine selected papaya varieties. The University of the Virgin Islands Agricultural Experiment Station is the only source for papaya seeds in the Virgin Islands.

Publications

• Zimmerman, TW and JA Kowalski. 2000. In vitro selection of transgenic immature zygotic papaya embryos. Congress on In Vitro Biology in San Diego, June 10-15, 2000, vol. 36 (in press).
• Zimmerman, TW. 2000. Papaya trees selected for the U.S. Virgin Islands. International Society for Tropical Horticulture, Homestead, September 24-29, 2000, vol. 44 (in press).

Progress 01/01/99 to 12/31/99

Outputs
Demand for locally produced papaya fruit far outweighs the supply in the U.S. Virgin Islands. Due to the high incidence of Papaya Ringspot Virus (PRSV), papayas are grown as an annual crop. The need exists in the Virgin Islands for papayas with early production to ensure a marketable crop before being devastated by PRSV. Breeding and selection has been ongoing for 5 years to develop papayas with tolerance to PRSV and fruit production starting at or less than 70 cm from the ground. The height at first fruit set, of 15 papaya cultivars recommended for the Virgin Islands, ranges from 58 cm to 253 cm. Generally, female plants start setting fruit lower on the stem than hermaphroditic plants. Through breeding and selection, three papaya lines have been developed which set fruit between 40 and 70 cm from the ground. These lines have also been selected for their tolerance to PRSV. These low-bearing papaya lines produce fruit that are marketable one month earlier than other cultivars.

Impacts
Local farmers and backyard growers of papaya will benefit from the low-bearing virus tolerant lines with reduced time to get production on the market to satisfy consumer demand.

Publications

• Zimmerman, T.W., J.A. Kowalski. 1999. Breeding and selection of low-bearing papayas in the Virgin Islands. HortScience 34:482-483.
• Kowalski, J.A., T.W. Zimmerman. 1999. The uses of papayas in the West Indies. Proc. 2nd International Medicinal Herb Conference (in press).