Investigation And Control Of Citrus Postharvest Diseases In The Main Producing Areas

Citrus is favored by consumers for high nutritional value and pleasant flavor.Postharvest rot caused by fungi during growth,processing,transportation,and storage is very serious and brings great economic losses to the citrus industry.In order to clarify the pathogen population structure and disease occurrence rule of main citrus varieties in various areas this study,seven varieties of Satsuma mandarin,Shatang mandarin,Ponkan mandarin,Nanfengmiju,Lane late navel orange,Newhall navel orange and Valencia orange were sourced from 13 areas,such as Wuhan,Yichang,Chenggu,Zigui,Lianshan,Dangyang,Xiangxi,Nanfeng,Ganzhou,Taizhou,Quanzhou,and Luodian,from 2019 to2021 and the postharvest diseases was identified.The results are as follows:1 、 The incidence of postharvest diseases: A total of 6609 citrus fruits and 1545 diseased fruits from 7 varieties in 13 areas were investigated from 2019 to 2021.The incidence ranged from 1.95% in Lianshan,Guangdong Province in 2021 to 87.18% in Chenggu,Shaanxi Province in 2019.The overall incidence reached 23.38%.2、Pathogen diversity of postharvest diseases of citrus: A total of 1483 fungal strains were isolated from 1545 diseased fruits.Based on the ITS sequences,they were identified to the genera Penicillium,Colletotrichum,Fusarium,Diaporthe,Clonostachys,Alternaria,Botryotinia,Geotrichum,Nigrospora,Lasiodiplodia,Neofusicoccum,Rhizopus,Cladosporium,Aspergillus,Phyllosticta,Aschersonia and Zasmidium.Among them,Penicillium,Colletotrichum,Alternaria and Fusarium were the dominant populations,accounting for 33.85%,24.75%,14.30% and 13.76%,respectively.3 、 Postharvest diseases of different varieties of citrus are different.Among the loose-skin citrus,the average incidence of Satsuma mandarin was 28.94%,19.42% for Ponkan mandarin,5.91% for Shatang mandarin,and 14.62% for Nanfengmiju.The average incidence of orange was 17.68% with 15.80% for Newhall navel orange and4.65% for Valencia orange.The main diseases of loose-skin mandarin fruit were blue/green mold and anthracnose,while blue/green mold and Fusarium stem rot for oranges.The postharvest diseases of the same citrus variety in different producing areas were significantly different.For Satsuma mandarin,the lowest incidence was 2.92% in Yichang,Hubei Province in 2020,and the highest was 87.18% in Chenggu,Shaanxi Province in 2019.The main disease was blue/green mold(32.40%)in Chenggu Shannxi while anthracnose(23.40%)in Wuhan,Hubei.In addition,black rot disease was also very serious in Chenggu,Shaanxi Province.As for Ponkan mandarin,the incidence in Xiangxi in Hunan Province was almost 40% in 2019 and 2020,while 5.33% in Dangyang Hubei Province in 2020.The main disease was blue/green mold in Xiangxi Hunan and Dangyang Hubei,while Fusarium stem rot and stem rot in Quanzhou Fujian.As for New navel orange,the incidence was 32.99% in Luodian Guizhou and as low as 8.7% in Zigui.The interannual occurrence dynamics of postharvest diseases in different varieties of citrus fruits.The incidence rate was more than 40% in the three years tested in Chenggu,Shaanxi,while was less than 6% in Dangyang Hubei.The incidence rates of postharvest diseases of Ponkan mandarin in Xiangxi Hunan and Quanzhou Fujian,Lane late navel orange in Zigui Hubei,Satsuma mandarin in Guilin Guangxi,and Newhall navel orange in Ganzhou Jiangxi were stable during the three years.The incidence varied from year to year in other areas.4、Identification of dominant pathogens.Based on the morphological characteristics and phylogenic analysis results,13 representative strains in the main pathogen group,Geotrichum,Diaporthe and Lasiodiplodia were identified as Fusarium lateritium,F.fujikuroi,Geotrichum citri-aurantii,Diaporthe citri,Lasiodiplodia citricola and L.theobromae.Among them,F.fujikuroi and L.citricola were first found to cause citrus fruit rot in China.5、Control of postharvest diseases of citrus: A study was conducted on the control of postharvest diseases in Satsuma mandarin from Yichang,Hubei in 2021.It was found that Prochloraz 1000 mg/L+Bellkute 800 mg/L significantly reduced the occurrence of postharvest diseases,while hot water,low concentration(Prochloraz 250 mg/L+ Bellkute200 mg/L)and medium concentration(Prochloraz 500 mg/L+ Bellkute 400 mg/L)showed no significant effects.In this study the occurrence of citrus postharvest diseases in the main producing areas was studied and the results provide important theoretical guidance for scientific control of citrus postharvest diseases.