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United States Department of Agriculture

Agricultural Research Service

Research Project: POSTHARVEST TREATMENT OF TROPICAL COMMODITIES FOR QUARANTINE SECURITY, QUALITY MAINTENANCE, AND VALUE ENHANCEMENT Title: Production of Internal Yellowing Symptoms on Resistant and Susceptible Papaya Cultivars by Enterobacter cloacae at Varying Inoculum Concentrations

Authors
item Nishijima, Kate
item Keith, Ronald - UH MANOA - CTAHR
item Fitch, Maureen
item Wall, Marisa
item Sugiyama, Lionel
item Nishijima, Wayne - UH MANOA - CTAHR

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 2, 2007
Publication Date: July 1, 2007
Citation: Nishijima, KA, RC Keith, MM Fitch, MM Wall, LS Sugiyama, and WT Nishijima. 2007. Production of internal yellowing symptoms on resistant and susceptible papaya cultivars by Enterobacter cloacae at varying inoculum concentrations. Phytopathology 97 (7): S84

Interpretive Summary: Internal yellowing (IY) is a bacterial disease of papaya characterized by yellow discoloration and tissue softening in ripening fruit. Populations of the causal agent, Enterobacter cloacae, may differ in resistant (R) or susceptible (S) cultivars and identifying R cultivars may help value-added products such as fresh or frozen papaya cubes conform to food safety guidelines. Fruit of four cultivars were examined to determine the population of E. cloacae in naturally infected fruit. Additionally, fruit of six cultivars were inoculated with two E. cloacae strains to evaluate for IY responses, rated IY1, IY2, or IY3 for slight, moderate, or severe symptoms, respectively. A naturally occurring population of E. cloacae was recovered at 4.17 x 10^5 colony forming units (CFU) per g from a Kapoho Solo fruit with IY3 symptoms. IY was absent in surveyed fruit of Rainbow, Sunrise and SunUp cultivars. Inoculations in the 10^9 to 10^10 CFU per ml range produced the most consistent results that clearly separated R and S cultivars. Sunrise was the most R (3% IY) followed by Rainbow F6 and SunUp (< 5% IY). Kapoho (90% IY) and Laie Gold and Kamiya (50 to 57% IY) were the most S. IY was absent in fruit of R cultivars Rainbow F6 and Sunrise when inoculated at low dose range 10^3 to 10^4 CFU per ml. Combining data for all dose treatments, Kapoho, Laie Gold, and Kamiya produced IY1, IY2 and IY3 symptoms, but R cultivars were never IY3. In reisolations from inoculated fruit, regardless of R or S cultivar the final E. cloacae populations increased by 3 to 6 Log10 orders from the initial dose treatments, except when the initial dose treatment was above 10^9 CFU per ml. At the high dose range, final populations decreased 2 to 3 Log 10 orders and may represent a saturation range for E. cloacae population.

Technical Abstract: Internal yellowing (IY) is a bacterial disease of ripening papaya flesh caused by Enterobacter cloacae and characterized by yellow softening tissue. IY restricts food safety of value-added products like fresh or frozen papaya cubes. The incidence of E. cloacae presumably differs in resistant (R) and susceptible (S) cultivars. Use of R cultivars could reduce food safety concerns. Fruit (140) of four papaya cultivars were examined for the presence of E. cloacae. Additionally, six cultivars were inoculated to establish their IY response. Sixty fruit per cultivar were inoculated (10^1 to 10^12 CFU/ml) with two E. cloacae strains or water, incubated at 28 ºC for 3 days, and scored IY1, IY2, or IY3 for slight, moderate, or severe symptoms, respectively. A naturally occurring population of E. cloacae was recovered at 4.17 x 10^5 CFU/g from a Kapoho fruit with IY3 symptoms. Rainbow, Sunrise, and SunUp were IY free. Inoculations in the 10^9 to 10^10 CFU/ml range produced the most consistent results that clearly separated R and S cultivars. Sunrise was the most R (3% IY) followed by Rainbow F6 and SunUp (< 5% IY). Kapoho (90% IY) and Laie Gold and Kamiya (50 to 57% IY) were the most S. The low dose range 10^3 to 10^4 CFU/ml produced IY in the three S cultivars and SunUp, but not in Rainbow F6 or Sunrise. Kapoho, Laie Gold, and Kamiya were IY1, IY2 and IY3, but R cultivars were never IY3. In all cultivars, final E. cloacae populations increased by 3 to 6 Log10 orders from the initial treatments except for those above 10^9 CFU/ml. At the high dose range, final populations decreased 2 to 3 Log10 orders and may represent a saturation range for E. cloacae.

Last Modified: 10/21/2014
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