Progress 09/01/10 to 08/31/13
Outputs
Target Audience: Presentations of project objectives and preliminary results were offered to local Hawaii growers at the annual meeting of the Hawaii Tropical Fruit Growers Association in Kona, Hawaii, on September 10, 2011. More complete information was presented to research peers at the 3rd International Symposium on Papaya in Chiang Mai, Thailand, December 19-21, 2011, and at the annual meeting of the Hawaii Tropical Fruit Growers Association at the University of Hawaii Manoa Campus on September 15, 2012. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? In October 2011, our Australian collaborator, Dr. Roderick Drew, visited the experimental field trial at Waimanalo, Oahu, in Hawaii and was given an update on progress in evaluating PRSV resistance in his plant materials. Two days of discussions involving Dr. Drew, the PI, and Co-PIs produced a plan of action for the completion of the project. In November 2011, the experimental field trial was used by the PI to demonstrate papaya breeding techniques to 8 students in TPSS453 Plant Breeding and Genetics. Subjects included pollination techniques, evaluation of virus disease symptomology, ELISA assays for PRSV detection, and fruit quality evaluation. How have the results been disseminated to communities of interest? Field tour and project overview for Society of American Foresters, November 2011. Field tour and project overview for Joint Meeting of the Second International Soil Sensing Technology Conference, the Soil Physics Technical Committee Annual Meeting, and the ASA Sensor-based Water Management Community, January 3-7, 2012. Presentations of project objectives and preliminary results were offered to local Hawaii growers at the annual meeting of the Hawaii Tropical Fruit Growers Association in Kona, Hawaii, on September 10, 2011. More complete information was presented to research peers at the 3rd International Symposium on Papaya in Chiang Mai, Thailand, and at the annual meeting of the Hawaii Tropical Fruit Growers' Association in Honolulu on September 15, 2012. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
The major findings included 1) plants inoculated at 5 mo. develop PRSV symptoms faster than those inoculated at 9 mo., 2) Hawaiian solo genotypes become infected more quickly and more severely than inter-generic BC progenies, and 3) no important differences were noted between mean ratings for inter-generic BCs and papaya recurrent parent line 5648 with regard to days to symptom expression, symptom severity, ELISA Abs. @ 405nm, or percentage of symptomless plants 4 mo. or 1 year after first inoculation.At the end of the project, all test plants had PRSV symptoms. Thus, while the test materials displayed generally good tolerance to PRSV relative to Hawaiian solo papayas, and remained productive throughout the trial, there was no evidence that BC lines that were presumed to have inherited the inter-generic resistance from Vasconcellea quercifolia were any more resistant than the negative control (recurrent parent line 5648) lacking those genes.
Publications
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Progress 09/01/11 to 08/31/12
Outputs
OUTPUTS: The field trial established at Waimanalo Experiment Station in May 2011 was manually inoculated with PRSV at monthly intervals in August, September, and October, when seedlings in the two blocks were 5 or 9 months old, respectively. Date of disease symptom onset and rating of symptom severity were recorded for each of the 354 plants, starting in September 2011. Objectives and early progress in the field trial were reported at the annual meeting of the Hawaii Tropical Fruit Growers Association, September 10, 2011, in Kona, Hawaii. Symptom development was documented with canopy photos in October and November 2011. In October, our Australian collaborator, Dr. Roderick Drew, visited the field trial and was given an update on progress in evaluating PRSV resistance in his plant materials. By late October 2011, with about 25 to 50% of the test plants showing PRSV symptoms, we began making crosses between symptomless selections and solo papayas. Crossing with solo varieties and some sibbed crosses continued throughout the reporting period. The 162 test plants in the first block were assayed by ELISA in November and December 2011 to confirm PRSV resistance or susceptibility and in an attempt to use the ELISA value as a quantitative estimate of virus titer and disease resistance. The results of evaluations conducted through 2011 were presented at the 3rd International Symposium on Papaya in Chiang Mai, Thailand, December 19-22, 2011. From March to May 2012, further ELISA were conducted, but results were found to be somewhat unreliable, with both false positives and false negatives appearing. Changing the extraction buffer did not correct these problems, so ELISA was discontinued as either qualitative or quantitative indicator of PRSV infection. By the end of the reporting period in August 2012, all but two test plants had developed at least mild PRSV symptoms. One of the symptomless plants was an individual of the backcross recurrent parent line (5648) used in these experiments as negative control for the Vasconcellea-derived PRSV-resistance. Seeds from a total of 49 fruits of selected symptomless or mildly symptomatic plants crossed with solo parents Sunset, Kapoho, or KpL8 were harvested and cleaned for storage. Three sib-crosses of the dioecious BC lines were also harvested for seed during the reporting period. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: Presentations of project objectives and preliminary results were offered to local Hawaii growers at the annual meeting of the Hawaii Tropical Fruit Growers Association in Kona, Hawaii, on September 10, 2011. More complete information was presented to research peers at the 3rd International Symposium on Papaya in Chiang Mai, Thailand, December 19-21, 2011. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
The major findings included 1) plants inoculated at 5 mo. develop PRSV symptoms faster than those inoculated at 9 mo., 2) solo genotypes become infected more quickly and more severely than inter-generic BC progenies, and 3) no important differences were noted between mean ratings for inter-generic BCs and papaya recurrent parent line 5648 with regard to days to symptom expression, symptom severity, ELISA Abs. @ 405nm, or percentage of symptomless plants 4 mo. after first inoculation. Thus, while the test materials displayed generally good tolerance to PRSV relative to solo papayas and remained productive throughout the trial, there was no evidence that BC lines that were presumed to have inherited the inter-generic resistance from Vasconcellea quercifolia were any more resistant than the negative control (recurrent parent line 5648) lacking those genes.
Publications
- No publications reported this period
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Progress 09/01/10 to 08/31/11
Outputs
OUTPUTS: During this initial reporting period, we addressed Objective 1: To determine the level and type of resistance to Hawaii strains of papaya ringspot virus (PRSV) operating in papaya plants from four segregating BC3 and BC4 populations derived by inter-generic hybridization with PRSV-resistant Vasconcellea quercifolia. Test seed was germinated in two equal batches temporally offset by four months (Dec 2010 and March 2011), and all potentially resistant materials were placed in tissue culture from shoot-tip explants to ensure protection of the unique germplasm. The seed had excellent germination, but because the first batch of seedlings had poor growth due to a toxic reaction to fungicide treatment (Ridomil Gold), we decided not to inoculate with PRSV in the greenhouse, but instead to move plants to the field before challenging with virus. The first batch of seedlings was planted in the field in a randomized complete block design in May 2010, five months after germination, together with susceptible controls (Kapoho and Davao Solo), a transgenic resistant control, and the backcross recurrent parent (5648). Each genotype was replicated three times with six plants per replication. The second batch followed into the field in July 2010, three months after germination, with a similar experimental design, except that each rep contained eight plants and the transgenic control was replaced with a third susceptible control, Sunset. Border rows included PRSV-susceptible solo cultivars Kapoho, Sunset, and KpL8 for use as crossing parents to achieve Objective 2: To make hybrids between the resistant BC3 and BC4 selections and non-transgenic Hawaii cultivars to begin transferring PRSV resistance to a solo genetic background. The first of three manual inoculations of the test materials with PRSV, made at one-month intervals, was accomplished in mid-August, using inoculum prepared by grinding leaf tissue of papayas infected with a local virus isolate in a mortar and pestle with 20 mM phosphate buffer (~1 : 30, wt./vol.). Two recently expanded leaves on each plant were lightly dusted with Carborundum and carefully rubbed with the pestle dipped in inoculum. PARTICIPANTS: Dr. Richard Manshardt, fruit crops breeder at the University of Hawaii at Manoa, is responsible for overall management of the project. He, Karen Pitz, and Steve Ferreira are executing the papaya ringspot virus resistance screening project at Waimanalo on Oahu. Dr. Steve Ferreira is a plant pathologist in the Plant and Environmental Protection Services Dept. at the University of Hawaii. He is responsible for overseeing the evaluation of the test plants for virus resistance. Karen Pitz, Junior Researcher in the Plant and Environmental Protection Services Dept. at the University of Hawaii, is responsible for assisting the PIs in inoculating and evaluating virus resistance in the test materials. Dr Maureen Fitch, consultant plant physiologist at the Hawaii Agriculture Research Center, is responsible for establishing and maintaining tissue cultures for safekeeping of irreplacable germplasm obtained from Drs. Drew and Siar, our collaborators in Australia and the Philippines, respectively. Dr. Rod Drew is a horticulturist in the School of Biomolecular and Physical Sciences at Griffith University in Brisbane, Australia and is a cooperator in our project as the developer of the intergeneric hybrid papayas. Dr. Simeona Siar is a plant breeder at Institute for Plant Breeding at the University of the Philippines in Los Banos, Philippines, and is a collaborator with Dr. Drew on the development of the PRSV-resistant backcrosses from the intergeneric hybrids. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
There are no outcomes to report at this point.
Publications
- No publications reported this period
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