Investigation On Disease And Insect Pests On Citrus In Jiangshan And Occurrence And Management Of Melanose

Citrus is an important economic crop in China,and melanose is one of the main diseases on it.In recent years,melanose is prevalent in citrus-producing areas,seriously decline the quality of fruit appearance and the value of commodity.This study investigate the variety of pests and diseases on citrus and occurrence regularity of citrus melanose in Jiangshan,Zhejiang Province,isolate and identify the Diaporthe spp.from citrus disease samples,determine the fungicide resistance to carbendazim of Diaporthe citri,carry out the fungicides screening against citrus melanose in vitro and in fields.The results provide scientific basis and reference for the research about diversity of Diaporthe spp.from citrus and prevention and control of citrus melanose.The main research results are summarized as follow:1.Investigation on species of citrus diseases and pests in Jiangshan.Based the investigation of the diseases and pests in the main citrus-producing areas of Jiangshan from 2020 to 2021,there are 26 kinds of pests,among them,the most serious pests were Aleurocanthus spiniferus,Toxoptera citricidus,Ricania speculum and Panonychus citri.There are 9 kinds of diseases,among them,the most serious disease was citrus melanose,followed by citrus anthracnose.2.Investigation on occurrence regularity of citrus melanose in Jiangshan.The results showed that the melanose of ponkan fruits began to appear in mid-May,its peak of disease occurred from mid-May to June,and there was no difference on disease index after mid-September.The highest of growth rate of disease index occurred from early April to early May on new leaves in spring shoot of ponkan and there was no difference on disease index after mid-October.The melanose of new leaves in spring shoot of grapefruit began to appear in mid-April.The growth rate of disease index increased quickly from mid-April to mid-May on new leaves of grapefruit and reached a peak in mid-August.Different species of citrus infected with citrus melanose have different situations.The morbidity of new leaves of grapefruit was heavier than that of ponkan,melanose also developed more rapidly.3.Isolation and identification of Diaporthe spp.from citrus in Jiangshan.In total,56 Diaporthe strains were derived from typical diseased samples in Jiangshan’s citrus orchards,16 representative strains were selected for morphological characteristics and multi-locus（ITS,tef1 and tub2）phylogenetic analysis.The results showed that these 16 strains belonged to 5 species of Diaporthe spp.,including D.citri（12 strains）,D.sennae（1 strain）,D.hongkongensis（1 strain）,D.unshiuensis（1 strain）,D.discoidispora（1 strain）.The results of in vitro inoculation experiments showed that all the five Diaporthe species could infect citrus.D.citri is the dominant pathogen of Diaporthe spp.on citrus in Jiangshan,D.sennae was first reported on citrus in Zhejiang Province.4.Resistance monitoring of D.citri to carbendazim and indoor fungicides screening.Differential dose method is used to determine the resistance levels of 35 D.citri strains from Jiangshan to carbendazim.The frequency of resistance to carbendazim is 37.04%,among them,8 strains were low resistance,8 strains were medium resistance,high resistance strain was not found.Making D.citri as the researching object,adopting mycelial growth rate method to fungicide screening in vitro,the results showed that the toxicity to D.citri from high to low is fluazinam,pyraclostrobine,difenoconazole,imazalil,mancozeb,with the EC₅₀of 0.133,0.166,1.41,2.132,82.769μg/m L.The EC₅₀of fluazinam and pyraclostrobine were both less than 1μg/m L,which can significantly inhibit the growth of mycelium.5.Field experiment on chemical control of citrus melanose.The results showed that the treatment with 80%mancozeb EW 600 had better control effect on citrus melanose.The second was the treatment with 1000 diluted multiples solution of 30%pyraclostrobine SC,the treatment with 1000 diluted multiples solution of 50%fluazinam SC,the treatment with 80%mancozeb EW 600 diluted multiples liquid and 30%pyraclostrobine SC 1000 diluted multiples liquid alternate use.In the cost comparison of fungicides,80%mancozeb EW and 30%pyraclostrobine SC cost were lower,so 80%mancozeb EW is current economical and effective fungicides for the control of melanose,30%pyraclostrobine SC can be used as an alternative fungicide.In the field control of melanose,the spring shoot germination stage of the fungicide control can effectively enhance the effectiveness of prevention and control.