Etiology, Occurrence And Control Of Papaya (Chaenomeles Lagenaria) Brown Rot

Papaya (Chaenomeles lagenaria) is a perennial plant native to China with an important role in the traditional medicine of several Oriental cultures. It is well-known for blood-dressed, antitumor, heart-strenghened and antiphlogistic activities. In recent years, a serious disease with brown rot on Papaya has been occurring and caused 60% yield losses in Changyang county, Hubei province, directly reducing local economic development and affected the exploitaiton of Papaya. The purpose of the current research was to identify the causal agent of the brown rot on papaya in China, to test the biological characteristics of the pathogen, and to determine the control techniques of this disease. The results were reported as follows:Monilia sp. was isolated from the diseased flowers, diseased fruits and diseased leaves of Papaya in the nursery of Changyang county, Hubei province, and then was proved as the pathogen of Papaya brown rot by inoculating mycelial plugs or conidial suspension of Monilia sp. onto healthy fruits. The colonies that cultivated on PDA were grey and the mycelium with septate and branches, the size of spores is 14-18×5-8um. The sequence of ribosomal DNA-ITS of this isolate was blasted to the Genbank, and the result showed a 99% homology to Moniliai. Therefore, the isolate was identified as Monilia mumecola based on the morphological characteristics and rDNA-ITS sequence.The results of biological characteristic showed that the pathogen could grow on PDA medium with or without illumination while the continuous illumination was the most suitable condition for the mycelia growth. The temperature range for mycelia growth was 10-30℃while 25℃was found to be the optimal one. The favorable pH value for mycelia growth was 3.0-11.0, with the optimal pH 5.5. The isolate could utilize various carbon and nitrogen sources, yeast and galactose were best for mycelial growth. The lethal temperature for mycelia and conidia was 55℃for 10 min and 65℃for 20 min, respectively. To determine the host range of Monilia mumecola, mycelial plugs were inoculated onto the healthy fruits of 12 plant . The result showed that the pathogen could infect Prunus salicina, Pyrus pyrifolia, Ziziphus jujuba and Malus pumilaThe observation on occurrence of Papaya brown rot in 2007,2008 and 2009 showed that the symptoms of flower rot occurred in early of March, peak of flower rot is from the mid-march to the end of March, the symptoms of fruit rot occurred in mid-April or end of April. At different elevations,the disease occurred date that the low elevations situation was earlier than the high elevations situation. The disease incidences of flowers and leaves were about 15 to 20 percent. The disease incidence of fruits was about 40 percent, and the highest is above 60 percent.Inhibition of mycelia growth of P. mumecola by four fungicides was assayed on amended PDA medium. 10% Score GR had the highest inhibitory effect with the 50% effective concentration (EC₅₀) at 0.21μg/ml whereas Chitosan had no inhibitory effect with the 50% effective concentration (EC₅₀) at 56837μg/ml. Field experiment for disease control indicated that the significant effect was observed with 500 times Score GR of 87.09% in blooming period, 83.97% in fruit setting and 37.88% in fruit developing. Effect of 1500 times Chitosan on control of the disease were the worst, with 32.95% in blooming period, 34.95% in fruit setting and 5.95% in fruit developing.