Identification of the pink disease for longan fruit in Hainan province

YANG Jihui; LI Peng; ZHANG Long; ZENG Yu; YANG Ye; FAN Yongmei

doi:10.13925/j.cnki.gsxb.20150409

Abstract：[Objective] Longan (Dimocarpus longana Lour.) is one type of evergreen tree,which is widely grown in the subtropical zone of South China.Along with the development of the longan industry,the diseases associated with this tree increased gradually.A new disease was discovered in Hainan,which occurs in the endangered growth stage of the longan fruit.According to its symptoms,it was named the "pink disease." This disease has been the most important factor influencing the quality and production of longan fruit.The objective of this study is to identify the pathogen and supply a theory as the basis for scientific control of this disease in the future.[Methods] Investigated the prevalent situation of the longan new disease in the field for three years in succession from 2013 to 2015.The longan fruit which had the pink disease were collected from the main producing areas in Hainan province.We identified the pathogen on the unhealthy longan through morphology and recorded the spore identified through morphology.One-centimeter disks of the diseased longan fruit were collected from the field and were cut and surface-sterilized with 75％ ethanol and 1‰ HgCl2.The disks were placed on a potato dextrose agar (PDA) medium in order to establish cultures at a temperature of 26-28 ℃ for 7 days.Each pure culture was obtained by subculturing hyphal tips onto anther fresh PDA plates,and separating the pured pathogen single spores.To confirm 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× lO5 CFU· mL-1) of the isolates and incubated at 20 ℃ and 100％ relative humidity with plastic and incurring natural cycles of light and darkness.Approximately 1 mL of conidial suspension solution was used for each group of Iongan fruit.The groups of longan fruit were sprayed daily with sterile double-distilled water.As negative controls,five groups of longan fruit from the longan trees were sprayed with water.Four to five days after inoculation,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 the isolated spores from the tie-back fruit with the spores isolated from the diseased fruit collected from the field.We extracted the genomic DNA from the pathogen,which was identified through 28S rDNA and ITS rDNA 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 were different.in different years.We identified the isolated pathogen.Through isolation and purification of the pathogeny from the diseased fruit from the field,we obtained 4 strains.We inoculated back the pathogeny to 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 to that of Trichothecium roseum.Conidiophore is colorless,erect,not branched,with no membrane or a small number of membranes,and sometimes the top inflates.The sporogenous cells produce spores by the sequence of the inverted axis being gradually reduced.The conidiophore is colorless,but pink when pies.It is pear-shaped or ovate.Its topmost circle is blunt and base ministry gradually becomes thin,and it becomes 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 GenBank,the homology was 99％.These studies suggested that the pathogen causing the longan fruit rot in Hainan Province was Trichothecium roseum.[Conclusion]The studies suggest that the pathogen causing the longan fruit rot in Hainan province was Trichothecium roseum.