Progress 09/15/04 to 09/14/07
Outputs
Papaya from the trees remaining in our commercial planting of the Slow ripening Line 4-16 were harvested every two weeks. Fruit stored at 10oC became more susceptible to postharvest disease than non-stored fruit as the length of storage time increased. Fungi decay was not immediately noticed upon removal from storage in fruit stored only for 2 weeks, decay developed subsequently during ripening at ambient temperature. The decay rate was recorded two days after fruit were removed to ambient temperature and increased dramatically from 12% to near 40% when storage period increased from 2 to 4 weeks. The decay rate was not significantly different due to the high standard variation. The susceptibility to decay varied greatly from season to season. Papaya fruit lost average 0.75 to 0.85% of fresh weight per day when ripen at ambient temperature. During cold storage, the weight loss was limited to less than 2% regardless the length of the storage. The weight loss increased to
1.2% to 1.45% per day when fruit were removed from cold storage to ambient temperature. Fruit stored at 10oC colored faster (7 to 8 days) when removed from 10oC and ripen at ambient temperature, than those without cold storage (8 to 10 days). This faster degreening and softening in flesh of cold stored fruit than non-stored fruit has been previously observed in Sunset papaya. Abnormal softening caused by chilling injury was observed in papaya stored for more than 3 weeks at 10oC. Chilling injury symptoms developed in fruit only after removal from cold storage and left to ripen at ambient temperature. The chilling injury symptoms were less obvious in fruit harvested during the warm season. Papaya harvested in spring showed a high rate of chilling symptom. The higher field temperature could have a preconditioning effect to prevent chilling injury. More fruit are needed to study the respiration, ethylene evolution and deformation changes following cold storage. The old field is not
producing enough healthy fruit for that part of the study due to the loss of 70% of the trees in 2006 after forty days of rain. We are waiting for fruit from a new field that has just started to set fruit. The effort to map the SSR markers for hard and soft papaya fruit is nearing completion. A total of 556 primers sets have been screened against hard and soft papaya parents, and 124 of these were found to show polymorphisms. Of these, 44 primers were selected at about 10 cM intervals throughout the 12 linkage groups. Two papaya parents producing hard fruit and two papaya parents producing soft fruit were chosen and compared to 176 F2 papaya plants chosen to represent the full range of fruit firmness phenotypic data as obtained from the field trial. To date, 39 primer sets have been completed on these 180 individuals. It is expected that all 44 primers will be done by the end of September. A spreadsheet containing all the summarized data is being developed and will be completed by the
end of September.
Impacts
The first outcome is the availability of naturally slow-ripening papaya lines that will enhance production and expand the marketing area. A second outcome is the acquisition of unique genetic markers for the slow-softening trait. Identifying these markers would be the first essential steps in a forward genetic approach to the isolation of the gene(s) involved in this unique character. If this character is controlled by a single gene, then it could become the basis for research on the control of fruit ripening. This has potential applications to other fruit.
Publications
- Chen, N. J., A. Manenoi, R. E. Paull. 2007. Papaya postharvest physiology and handling - problems and solutions. Acta Horticulturae 740:285-294.
- Thumdee, S., A. Manenoi, R. E. Paull. 2007. Activity of papaya fruit hydrolases during normal and modified ripening. Acta Horticulturae 740:317-322.
- Manenoi, A., R. E. Paull. 2007. Papaya fruit softening, endoxylanase gene expression, protein and activity. Physiologia Plantarum 131:470-480.
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Progress 10/01/05 to 09/30/06
Outputs
The two large experiments associated with this project were installed and data is being taken. On Poamoho Experimentation Station the slow ripening parents, F2 population and F1 backcross material was planted. On a private contractors property a large planting of two of the slow ripening lines was made and reached the fruiting stage. Fruit were harvested from parents and segregating populations and parents and evaluated for ripening rate and firmness. A minimum of ten fruit have been harvested from each tree with more than 90% of the trees already sampled. Ripening rate was evaluated on a softening index based upon the days taken relative to full yellow stage to become soft. The index therefore can be positive or negative; a negative value indicating the fruit became soft before it reach full yellow skin color. Some variation was found with fruit from the same tree. The average softening score was used to compare tree softening. The softening index varied from -2.9 to
+5.2 with the mean being 0.37. When the frequency distribution was plotted it showed a central peak with a normal distribution with a median value of 0.29. On either side of this main central peak there were two smaller peaks. From the 401 F2 trees, about 50 of each F1 backcross trees and eight of each parent, young leaf samples were harvested and stored at -80C. DNA was then extracted from the leaf samples. We have screened 630 primer sets from selected parents and F2 tree leaf samples for polymorphisms. Another 175 primer sets that have been mapped are now being evaluated. One primer set shows possible linkage to the slow ripening trait. In the block planting in the contractor's field the establishment and early growth was excellent. As the trees began to set fruit individual tree we marked as early fruiting and these and other trees were evaluated for column compactness and fruit size. By January, most of the trees were fully laden with developing fruit and we began to harvest a
few fruit. In February/March we had almost continual rain with at period of about two weeks in which the rain was incessant. It was difficult to get into the field during this period even though the area was very well drained. By the time, we were able to easily get back into the field on a regular basis, it became clear that Phytophthora stem canker and root rot were having an effect. The adjoining grower's field was also going down as the area was SunUp which has the same variety Sunset in its background as our slow ripening line that is known to be susceptible to Phytophthora. Only about 20% in the trees in the end survived. We have been marking the remaining trees for the slow ripening trait and selfing flowers if the trees have no summer sterility. To carry out the storage studies, we have had to resort to replication though weekly sampling. Initial results suggest that the slow ripening material has a similar storage characteristic as the parent. We are replanting a small repeat
of this experiment on Poamoho though it will not been available before the end of this project.
Impacts
The first outcome is the availability of naturally slow-ripening papaya lines that will enhance production and expand the marketing area. A second outcome is the acquisition of unique genetic markers for the slow-softening trait. Identifying these markers would be the first essential steps in a forward genetic approach to the isolation of the gene(s) involved in this unique character. If this character is controlled by a single gene, then it could become the basis for research on the control of fruit ripening. This has potential applications to other fruit.
Publications
- Chen, N. J., Paull, R. E., 2006. Applicacoes do biotechnologia na pos-colheita de frutos: progressos e limitacoes. Proceeding of the XIX Congresso Brasileiro de Fruticultura, Cabo Frio, RJ. Brazil, 17 to 22 September. p 87-94.
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Progress 10/01/04 to 09/30/05
Outputs
The primary objectives of this proposal are to determine the performance of natural slow ripening lines in a semi-commercial field planting, make additional selections, and carry out in-depth storage studies. The secondary objectives are to determine the inheritance of the trait and to isolate markers using amplified fragment length polymorphisms (AFLPs). Rain in November and again in February and March delayed land preparation and field plantings for Objective 1 with a cooperator and Objective 2 (Poamoho Experiment Station). The two lines of 4-16 were planted in the cooperating grower's field in late April. The plants have flowered and were thinned in late August/early September, fruit are being set. Initial selections have been made for early fruiting, column density, fruit shape and summer sterility. Sixteen trees out of 240 have been marked. Selfing of these trees has started. The parents and F2 segregating population of a cross of line #8 and line #4-16 were
planted at Poamoho Experiment Station in May. Plant growth were initially slow due to the delay in field planting due to wet weather and magnesium deficiency. The plants, after remedial action, are growing well and flowering. Some of the early F2 and parents have fruit at the color break stage. Once flowering is more uniform and fruiting more advanced, leaf samples will be taken for DNA extraction. When fruit begin to ripen the trees will be evaluated for ripening rate and the DNA bulked for AFLP analysis.
Impacts
The first outcome is the availability of naturally slow-ripening papaya lines that will enhance production and expand the marketing area. A second outcome is the acquisition of unique genetic markers for the slow-softening trait. Identifying these markers would be the first essential steps in a forward genetic approach to the isolation of the gene(s) involved in this unique character. If this character is controlled by a single gene, then it could become the basis for research on the control of fruit ripening. This has potential applications to other fruit.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
The project was initiated by the planting of the F-1 seeds, the parents and two back-cross lines at Poamoho Experiment Station on Oahu. Leaf sampling will take place after transplanting. The planting of the slow-ripening line (4-16) in a commercial field is being coordinated with the grower. The planting is scheduled for the new year on the north shore of Oahu.
Impacts
The objective of this project is to determine the inheritance of the slow-ripening trait. This would open a door to our understanding the regulation of fruit ripening. AFLP markers may provide unique information as to the genetic loci involved in this altered ripening pattern. This information (inheritance and molecular markers) could lead to the isolation of the gene(s) involved in this trait that may have potential applications in other fruits.
Publications
- No publications reported this period
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