Progress 09/28/00 to 09/27/05
4d Progress report. This report documents research conducted under a Grant agreement between ARS and the University of Hawaii at Manoa. Additional details of research can be found in the report of the associated in-house CRIS 5320-22430-021- 00D, Detection, Control, and Areawide Management of Fruit Flies. Pest Status of White Peach Scale (Pseudalulacapspis pentagonia, Homoptera; Diaspididae) in Hawaii and Biological Control Opportunities: White peach scale has not yet invaded Oahu. All plantations on Oahu, irrespective of variety grown, locality, and conditions of plants are free from infestation. Papaya fruit infested with dead white peach scale have been found in stores on Oahu. Unfortunately, all growers on Hawaii are experiencing extensive problems with this pest on the Big Island. Surveys were conducted in the Hilo and Pahoa area to determine density of infestation. Surveys of biological control agents have shown that there are a number of ladybug species that
prey on the scales. Some minute aphelinid wasps have also been reared from scales. Permission is being sought to implement biological controls using an imported parasitoid wasp. With the recent discovery of papaya mealybug (Pseudococcidae, Paracoccus marginatus) on Maui, monitoring surveys will include this potential devastating pest of papaya. Comparison of Yield and Quality of Papaya Ringspot Virus (PRSV) Resistant, Micropropagated Papaya Selections in Different Environments: Problems were encountered with culture contamination and were solved by adjusting tissue culture media and micropropagation protocols. Losses that had been high were reduced; transplant survival from tissue culture to greenhouse was more than 90% due to improved shoot and root development in tissue culture. The addition of a new step, the rooting of cuttings of large micropropagated plants maintained in the greenhouse, increased the output of plants for the three location field test of Laie Gold that was
installed in Kahaluu, Kahuku and Haleiwa in February 2005. The Kapoho hybrid clones will not be tested. Use of cloned hermaphrodites could result in savings despite the cost of cloned plants (current $1.50 for a small Rainbow plant) because farmers would be freed of the need to purchase see, sow and care for the seedlings during germination (sometimes it is poor or pests, re-seeding is required), multiple plant and thin to a single hermaphrodite. These costs would be eliminated to the farmer. An article on papaya micropropagation, Papaya! High-tech tactics enhance a tropical favorite was featured in the USDAs Agricultural Research magazine, January 2004, Vol 52, No. 1, ISSN 0002-161X, pp.1,2, 4-7, that is published monthly: www.ars.usda.gov/is/AR. Handling, Storage and Simulated Shipment of Transgenic Ringspot Resistant 'Rainbow' and 'Sunup': This years focus has been the continued application of the ethylene inhibitor, 1-methylcyclopropene (MCP) to papaya in stimulated post
harvest handling. MCP has the potential to extend the post harvest handling period and add efficiency to papaya supply chain management. We have found continued problems in MCPs application to papaya and have had hesitation to recommending it to Hawaiis packers and shippers. An explanation of the problems would enable us to make reliable recommendations. This would be of direct benefit to all Hawaiis papaya packers and shippers. MCP has been approved for post harvest use on fruits and vegetables. MCP-treated papaya had delayed ripening when compared to the non-MCP treated fruit. When fruit were treated with MCP at different stages of skin color (yellow): 10%, 20-30%, 40-50% and 60- 70%, ripening was delayed by approximately 7, 5, 2 and 1 day, respectively. MCP treated fruit at 10 % and 30% skin yellowing (after cold storage) showed delayed ripening of approximately 4 and 2 days, respectively. Fruit treated with MCP at different stages resulted in different firmness when full
ripened. The 10 % yellow fruit gave the highest firmness and had a rubbery texture. Fruit treated at riper stages were slightly firmer than the control without the rubbery texture. There was no difference in weight loss between MCP-treated fruit and the non-treated control fruit. Post harvest disease control was essential in order to gain the benefit of MCP treatment. Control was obtained by using hot water at 49 oC for 20 minutes followed by immersion in 650 ppm of TBZ before starting the experiment. Even following this treatment there was slightly higher disease incidence in MCP treated fruit than non-treated control fruit at full ripeness.
Progress 10/01/03 to 09/30/04
4. What were the most significant accomplishments this past year? This report serves to document research conducted under a grant agreement between ARS and the University of Hawaii. Additional details of research can be found in the report for the parent CRIS 5320-22430-020-00D, Biology, Control, and Areawide Management of Fruit Flies and Other Pests. Pest Status of White Peach Scale (Pseudalulacapspis pentagonia, Homoptera; Diaspididae) in Hawaii and Biological Control Opportunities. Project is assessing the extent of infestation and impact of P. pentagonia on papaya production in Hawaii. A large scale infestation of white peach scale on papaya was discovered in Keeau region of Hawaii. Environmental characteristics that encourage white peach scale infestations, such as wet weather encourages infestations are under investigation. Search for parasitoids is underway. Developing and utilizing synthetic genes for broad and stable resistance to Papaya ringspot virus. Two
synthetic gene constructs that correspond to the variable and the constant regions of the coat protein gene of Hawaii, Thailand, and Taiwan papaya ringspot virus (PRSV) isolates were designed, synthesized, and cloned into vectors. New this year is that it appears that these transgenic papayas are resistant to more than one PRSV strains. In addition, some lines gave resistance to not only all three major PRSV strains but were resistant to a new disease papaya leaf distortion virus - a disease that causes similar destruction to papaya trees but is not related to the PRSV virus. Virus Resistant Kapoho with Higher Level of Resistance to Post Harvest Fungal Diseases Through Development of Transgenic Plants with Delayed Fruit Softening Characteristics. Eight different constructs were developed and used to engineer Kapoho and Sunrise varieties with constructs that combine both the coat protein gene from papaya ringspot virus (PRSV) and a beta-galactosidase gene from papaya. These
transformations should provide protection from disease as well as silencing the beta-galactosidase gene resulting in firmer fruit with delayed softening characteristics. Additional transformants were selected and planted in the greenhouse for screening for resistance of PRSV. Resistant plants were planted in the field to produce R1 and R2 lines. This work is ongoing. Homozygous lines will be characterized for fruit ripening and compared to Kapoho and Sunrise controls. Comparision of Yield and Quality of Papaya Ringspot Virus (PRSV) Resistant, Micropropagated Papaya Selections in Different Environments. Selections of papaya trees bearing full fruit columns of relatively large, well-formed, uniform fruit were made on the same trees during different seasons of the year. Since weather conditions affect fruit production, multiple observations gave a more accurate assessment of the trees' overall performance. About 100 trees of the Laie Gold (Kamiya) and 50 Kapoho type were selected
after 2-6 observations at different times of the year. Branches from the trees were collected and placed into tissue culture with the intent to reproduce thousands of the same clones. By the end of the first year, 29 superior Laie Gold and 18 superior Kapoho hybrids were in micropropagation. These trees will be evaluated in the field once they are ready. Selections of Kapoho backcross (Poamoho Gold x Kapoho progeny) continue to be made on trees on farms in Keeau and Haleiwa. The Haleiwa clones were planted for further observation. Backcross selections for low bearing height in addition to good quality. The backcross clones produced carpellodic fruit but the Rainbow did not. Handling, Storage and Simulated Shipment of Transgenic Ringspot Resistant 'Rainbow' and 'Sunup'. Use of MCP for 24 hours resulted in papayas that were firmer and the time to reach edible stage was always longer. However, the onset of disease, though later than controls and lesser in severity, negated the
advantages of MCP treatment on shelf life. Inconsistent responses to MCP treatments were observed.