Abstract:

【Objective】 To effectively control citrus huanglongbing (HLB, yellow shoot disease), the distribution, damage and epidemics of the disease were investigated in Fujian Province. 【Method】 The distribution of “Candidatus Liberibacter asiaticus”, the putative pathogen, the Asian citrus psyllid (Diaphorina citri), the insect vectors, and the incidence of HLB were investigated in 245 citrus-producing towns in 48 counties in Fujian Province. Polymerase chain reaction (PCR）assay was carried out to verify the existence of HLB in the collected blotchy mottle leaves and color inversion fruits to analyze the epidemics of HLB. Sliding correlation analysis was applied to select climatic factors associated with HLB occurrence. 【Result】 HLB and D. citri could be observed in all citrus-producing towns and all counties in Fujian with the northern limit of N28°07′ and the altitude of 880 m. The average incidence rate of HLB was 16.59% in Fujian. Significant difference in incidence rate was observed in different varieties with an increasing order of pummelo, sweet orange, mandarin (Citrus reticulata Blanco.) The incidence of HLB was negatively correlated with latitude, altitude, slope of orchard. The field incidence was only related to the climate of the last 2 springs in Changtai county (N24°7′) in subtropical zone, with a positive correlation with the sunshine in spring flush period and a negative correlation with the humidity in young fruit period. Therefore, drought in spring could be related to the epidemic of HLB. The color inversion fruits and blotchy mottle leaves are the typical characteristics of HLB, in which “Candidatus Liberibacter asiaticus” were detected in 93.8% and 73.1% of the samples by Nested-PCR, respectively. The reliability of the former is higher than the latter. 【Conclusion】“Candidatus Liberibacter asiaticus”and D. citri could be observed in all citrus-producing areas in Fujian. The outbreak of HLB could occur in severe drought areas in spring. The color inversion fruit could be used to diagnose HLB in fields.

Key words: Huanglongbing, field incidence rate, epidemic, epidemic climate, color inversion fruit