Identification of the pink disease for longan fruit in Hainan province

Abstract: 【Objective】Longan(Dimocarpus longana Lour.) is one type of evergreen tree, which is widelygrown in the subtropical zone of South China. Along with the development of the longan industry, the dis-eases associated with this tree increased gradually. A new disease was discovered in Hainan, which oc-curs in the endangered growth stage of the longan fruit. According to its symptoms, it was named the“pinkdisease.”This disease has been the most important factor influencing the quality and production of longanfruit. The objective of this study is to identify the pathogen and supply a theory as the basis for scientificcontrol of this disease in the future.【Methods】Investigated the prevalent situation of the longan new dis-ease in the field for three years in succession from 2013 to 2015. The longan fruit which had the pink dis-ease were collected from the main producing areas in Hainan province. We identified the pathogen on theunhealthy longan through morphology and recorded the spore identified through morphology. One-centi-meter disks of the diseased longan fruit were collected from the field and were cut and surface-sterilizedwith 75% ethanol and 1‰ Hg Cl2. The disks were placed on a potato dextrose agar(PDA) medium in orderto establish cultures at a temperature of 26-28 ℃ for 7 days. Each pure culture was obtained by subcul-turing hyphal tips onto anther fresh PDA plates, and separating the pured pathogen single spores. To con-firm the Trichothecium roseum isolates as the causative pathogen, healthy longan fruit(five bunches of longan fruit) from longan trees were sprayed with a conidial suspension(approximately 1.0×105CFU·mL^-1) ofthe isolates and incubated at 20 ℃ and 100% relative humidity with plastic and incurring natural cyclesof light and darkness. Approximately 1 m L of conidial suspension solution was used for each group of lon-gan fruit. The groups of longan fruit were sprayed daily with sterile double-distilled water. As negativecontrols, five groups of longan fruit from the longan trees were sprayed with water. Four to five days afterinoculation, lesions started to form on the longan fruit which were sprayed with the putative Trichothecium roseum isolates and the symptoms were quite similar with that of the other fields. We then compared theisolated spores from the tie-back fruit with the spores isolated from the diseased fruit collected from thefield. We extracted the genomic DNA from the pathogen, which was identified through 28 S r DNA and ITSr DNA sequence analysis. We sequenced using the NCBI database, to obtain the results of the Blast alignment.【Results】The investigation results showed different regions of the disease incidence and index weredifferent.in different years. We identified the isolated pathogen. Through isolation and purification of thepathogeny from the diseased fruit from the field,we obtained 4 strains. We inoculated back the pathogenyto the longan fruit. The disease symptoms after inoculation were the same as that on the collected samples,which showed that the fungus was the pathogen. The conidia' morphology of the pathogen were similar tothat of Trichothecium roseum. Conidiophore is colorless, erect, not branched, with no membrane or a smallnumber of membranes, and sometimes the top inflates. The sporogenous cells produce spores by the se-quence of the inverted axis being gradually reduced. The conidiophore is colorless, but pink when pies. Itis pear-shaped or ovate. Its topmost circle is blunt and base ministry gradually becomes thin, and it be-comes bispore. The size of the spores are usually(13.9-22.4) μm×(7.5-12.5) μm and the average is 18.6 μm×11.0 μm. Comparing the measured sequence with the related sequence in the Gen Bank,the homolo-gy was 99%. These studies suggested that the pathogen causing the longan fruit rot in Hainan Provincewas Trichothecium roseum.【Conclusion】The studies suggest that the pathogen causing the longan fruit rotin Hainan province was Trichothecium roseum.