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1) To confirm in the parents (SunUp and Kapoho), F1 progeny (Rainbow), and F2 segregating progeny (selfed seedlings from Rainbow) that SunUp (and Sunset) is highly resistant, Kapoho is highly susceptible, Rainbow is moderately resistant/susceptible, and the progeny range from resistant to susceptible to E. cloacae, the causal agent of internal yellowing of papaya fruit. 2) To calculate the ratio of RBF2 progeny that segregate for resistance and susceptibility to determine if the ratio is Mendelian indicative of genetic transmission of a disease resistance gene(s) and to use DNA data from 95 RBF2 individuals in another study to try to identify a resistance gene marker. 3) To carry out recurrent selection as well as initiate micropropagation of selections highly resistant to E. cloacae and exhibiting good handling characteristics and other high quality traits of Kapoho and other cultivars. 4) To analyze the food quality, microbial flora, and vitamin content of E. cloacae resistant and susceptible lines for use in value-added products, specifically fresh and frozen papaya cubes.
Non-Technical Summary: Internal Yellowing of papaya is caused by a coliform bacterium and causes an off-color and a bad smell of the flesh. It cannot be observed without cutting the fruit open. This project will identify and determine the inheritance of resistance to the bacterium so lines of papaya can be selected for commercial use to minimize its occurrence, especially in fresh and frozen papaya cubes. <P> Approach: 1) Fruits from parents and progeny will be collected from fields on Kauai, shipped to Hilo and inoculated with a tuberculin syringe with several strains (ginger, papaya, and Oriental fruit fly) of the causal bacterium. After inoculation, fruits will be boxed and incubated for 2-3 days and evaluated for symptom development. Data will be summarized and statistically analyzed. 2) Fruit from 95 individual progeny will be selected for DNA analysis in a QTL study and from other trees in the Kauai planting. Results will be submitted to chi-square analysis to determine if there is a single Internal Yellowing resistance gene. 3) Internal Yellowing resistant Rainbow F2 trees with good fruit and growth characteristics will be micropropagated and seeds will be conserved as well as planted to test F3 populations for inheritance of resistance. Papaya lines will be selected for quality traits such as full fruit columns of uniform, attractive fruit of about 600 g weight, low incidence of carpellody, firm flesh, smooth texture, attractive flesh color, and vigorous tree growth habit as well as resistance to Internal Yellowing. 4) Quality, microbial, and compositional analyses will be performed on fresh and frozen papaya cubes prepared from resistant and susceptible lines. Ascorbic acid (Vitamin C), carotenoids (provitamin A and lycopene) and sugar contents will be analyzed using HPLC. Surface color, flesh firmness, pH, microbial assays (standard plate counts, coliform counts, and E. coli counts) will be performed.