Studies On The Distribution And Control Technology Of Citrus Huanglongbing In Hunan Province

Citrus is one of the most important fruits in China and even in the world.It is the third largest global traded agricultural product after wheat and corn.China,as a big country of citrus production,has the largest production and planting area in the world.Citrus Huanglongbing(HLB)is the most destructive citrus disease in the world,which seriously threatens the yield and quality of citrus and causes huge economic losses.At present,there was no specific agent to cure the disease,and aslo there was no specific disease resistant citrus varieties for cultivation.Therefore,it was mainly through digging out diseased trees,controlling citrus psyllid and planting disease-free seedlings to prevent and control citrus HLB by now.As one of the main production areas of dominant citrus,Hunan province is located in the golden zone of citrus industry development in China.Therefore,the prevention and control of citrus HLB and its research in Hunan province are very important.In recent years,through field investigation and literature review,we had conducted preliminary investigation and analysis on the planting distribution of citrus,the main occurrence areas of HLB,the impact of HLB on citrus production and the main control measures taken in Hunan province.And combined with field experiments,the combination of control agents had been screened.The main research results are as follows.1.In recent years,the occurrence area of citrus HLB in Hunan province had been expanding,from 13 counties(districts)where the disease occurred in 2012 to 28 counties(districts)in 2019.At present,the occurrence area of citrus HLB had reached more than180,000 mu,and more than 7 million diseased trees had been cut down in Hunan province from 2015 to 2018.The status of prevention and control was very serious.2.The results of field trials showed that the contents of chlorophyll a,chlorophyll b and carotenoids in citrus infected with HLB were generally lower than those in healthy plants,and the net photosynthetic rate,transpiration rate and instantaneous water use efficiency decreased significantly with the development of the disease.In contrast,starch and soluble sugar accumulated in leaves of the affected plants,and the electrical conductivity increased significantly which resulted from cell membrane damaged.3.In the early stage of citrus HLB infection,the No.4 treatment of agent combination "(600 times golande + Hainan oligosaccharide)spray + eurogge 100 times root irrigating" and the No.3 treatment of agent combination "(600 times golande +14-hydroxybrassicin sterol 98%)spray + eurogge 100 times root irrigating" could effectively inhibit the development of HLB and reduce the hurts of citrus HLB.The treatment effect of other combination was not obvious.For the severe infection plants,the five treatment combinations could not effectively inhibit the development of HLB.To sum up,in order to realize the healthy development of citrus industry in Hunan province and even in China,although there is no specific agents for eradicating HLB at present,according to the pathogenesis regularity and the way of pathogen transmission of citrus HLB,at the beginning of infected HLB,the agents screened could be used effectively restrain the development of HLB germs.At the same time,the comprehensive and control measures by strengthening the quarantine and supervision of seedling,prevention psyllid,and thoroughly clean up severely infected plants,had been proved to be effective in practice.