Hao J J, Subbarao K V
Department of Plant Pathology, University of California, Davis, c/o United States Agricultural Research Station, Salinas, CA 93905.
Plant Dis. 2005 Jul;89(7):717-725. doi: 10.1094/PD-89-0717.
Temporal and spatial patterns of lettuce (Lactuca sativa) drop caused by Sclerotinia minor and S. sclerotiorum were determined in lettuce fields in the Salinas, Santa Maria, and San Joaquin Valleys in California during 1995 to 1998. Of the 25 commercial fields assessed, 14 had predominantly S. minor, 9 had predominantly S. sclerotiorum, and 2 had varying levels of both species. Sclerotinia infections were classified based on symptoms: those caused directly by eruptive germination of sclerotia (type I) and those caused by the airborne ascospores (type II). The precise location of diseased and healthy plants was mapped and lettuce drop progress was determined at different crop growth stages. Spatial patterns of disease incidence were analyzed using 1-by-1-, 2-by-2-, 3-by-3-, and 4-by-4-m quadrat sizes. Regardless of the analytical method employed, disease incidence with type I infection showed an aggregated pattern in a majority of the fields evaluated and random patterns in fields where incidence was low. In all fields with type I infection, disease progress followed the monomolecular model, typical of soilborne diseases. For fields with aggregated distribution, spatial dependence was observed up to 10 m and was either isotropic or random in direction, suggesting the potential influence of tillage operations on inoculum distribution and disease incidence. Lettuce drop incidence in fields with type II infection was erratic in time and peaked within a very short time. However, disease incidence showed an aggregated pattern in all fields evaluated. Spatial dependence of quadrats generally was detected in two adjacent directions, suggesting a directional gradient perhaps caused by wind direction during ascospore dissemination. Increasing quadrat sizes usually increased the degree of aggregation of lettuce drop, but not the distribution pattern itself. These results demonstrate that the source of inoculum and the type of infections they cause are most likely to determine spatial patterns of lettuce drop in the field.
1995年至1998年期间，在加利福尼亚州的萨利纳斯、圣玛丽亚和圣华金河谷的生菜田中，确定了由小核盘菌和核盘菌引起的生菜腐烂病的时空模式。在评估的25个商业田中，14个主要感染小核盘菌，9个主要感染核盘菌，2个两种菌的感染程度不同。核盘菌感染根据症状分类：由菌核爆发性萌发直接引起的（I型）和由气传子囊孢子引起的（II型）。绘制了患病和健康植株的精确位置，并确定了不同作物生长阶段生菜腐烂病的发展情况。使用1×1米、2×2米、3×3米和4×4米的样方大小分析病害发生率的空间模式。无论采用何种分析方法，I型感染的病害发生率在大多数评估田中呈聚集模式，在发病率低的田中呈随机模式。在所有I型感染的田中，病害发展遵循单分子模型，这是土传病害的典型特征。对于分布聚集的田块，观察到空间依赖性可达10米，且方向上要么各向同性要么随机，这表明耕作操作对接种体分布和病害发生率有潜在影响。II型感染田块的生菜腐烂病发病率随时间变化不稳定，且在很短时间内达到峰值。然而，在所有评估田中病害发生率均呈聚集模式。样方的空间依赖性通常在两个相邻方向上检测到，这表明可能是子囊孢子传播期间风向导致的方向梯度。增大样方大小通常会增加生菜腐烂病的聚集程度，但不会改变分布模式本身。这些结果表明，接种体来源及其引起的感染类型最有可能决定田间生菜腐烂病的空间模式。
