Spatial Pattern of Bacterial Leaf Blight of Rice in Commercial Fields

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae , is a major threat to rice production. To characterize the field-scale spatial structure of BLB under commercial conditions, disease incidence and disease index in 11 naturally infected rice fields in Taizhou, Zhejiang Province, China. Disease incidence ranged from 51.54% to 93.56%, and disease index ranged from 41.59 to 73.75. The index of dispersion was >1.0 in all fields and differed significantly from a random binomial expectation ( P < 0.0001), indicating overdispersion. Binary power law described the relationship between observed and binomial variances on logarithmic scales (R2 = 0.774); however, no consistent incidence-dependent aggregation pattern. Variance of moving window averages indicated positive spatial association in most fields at small to intermediate window sizes, particularly from 2×2 to 6×6 quadrats. Semivariogram analysis of trend-adjusted BLB incidence data detected significant spatial dependence in all 11 fields ( P < 0.05), with estimated ranges from 1.57 to 6.27 m. Spherical models fitted the empirical semivariograms well in several fields (R2>0.90), and the proportion of structural variation varied among fields from 0.248 to 1.000. Semivariograms based on disease-index data produced spatial patterns comparable to those based on incidence. Overall, BLB was found to have field-scale overdispersion and local spatial dependence as expected due to fine-scale clustering which could be linked to localized spread, water-mediated dispersal, or spatial heterogeneity in the field. These results confirm spatially distributed sampling designs and indicate that localized surveillance can enhance BLB monitoring in commercial rice fields.