Abstract: In order to reveal the spatial distribution and infection characteristics of PCR positive strains of Citrus Huanglongbing in Zhejiang Province, PCR method was used to sample and detect 2 900 orange trees scattered in 7 different locations where Citrus Huanglongbing occurred during the year 2017 and 2018. Ten strains were clustered as a group, 290 groups of sample data were obtained. The spatial distribution pattern of Citrus Huanglongbing was determined by aggregation index method. The results showed that C>1, I>0, K>0, C_A>0, M^*/$\bar{x}$>1, were aggregation distribution patterns, indicating that the distribution of Citrus Huanglongbing PCR-positive plants tended to aggregation distribution. The regression test of Iwao's M^*-$\bar{x}$ linear model indicated that the basic components of spatial distribution of Citrus Huanglongbing PCR-positive plants were individual groups. The PCR-positive plants attract to each other, thus making a clear distributive focus of diseases in the citrus orchard. The analysis of Taylor's V-$\bar{x}$ power law model showed the spatial distribution to be density-dependent, the higher the density of positive plants, the more tendency to aggregate distribution, meaning the intensity of aggregation increases with growing positive rate. The theoretical sampling model was N=1.962/D²[1.6976/$\bar{x}$-0.9296], while the sequential sampling formula was T_n=1.6976/[$D^{2}_{0}$+0.9296/n]. The application of these parameters was of great significance in improving monitoring efficiency and early-warning of Citrus Huanglongbing, as well as making control decisions.

Key words: Citrus Huanglongbing pathogen, PCR-positive plant, distribution pattern, sampling techniques