Hao J J, Subbarao K V
Department of Plant Pathology, University of California, Davis, c/o U.S. Agricultural Research Station, 1636 E. Alisal St, Salinas, CA 93905.
Plant Dis. 2006 Mar;90(3):269-278. doi: 10.1094/PD-90-0269.
Field experiments were conducted to determine the population dynamics of Sclerotinia minor and incidence of lettuce drop at two sites during 1995 to 1998. Rotation treatments at the Spence site, which had a low density of inoculum (<7 sclerotia per 100 cm of soil) that was distributed randomly, included: continuous lettuce (LLL), lettuce rotated with broccoli (LBL), and lettuce followed by a fallow period (LFL). Treatments at the Hartnell site, which had a high density of inoculum (>7 sclerotia per 100 cm of soil) that was distributed uniformly, included: continuous lettuce (LLLL), alternate crops of broccoli and lettuce (BLBL), continuous broccoli or lettuce (BBLL), and fallow-lettuce-fallow-lettuce (FLFL). Under continuous lettuce cropping (LLLL) at the Hartnell site, a progressively aggregated spatial pattern of inoculum distribution developed, despite the initial uniform distribution of high inoculum density. In the fallow treatment (FLFL), the spatial pattern tended to be aggregated following a lettuce crop and less aggregated or random when left fallow. In contrast to these two treatments, treatments involving rotations with broccoli (BLBL and BBLL) exhibited consistently random spatial patterns of inoculum regardless of the crop in the field. The marginal increases in the number of sclerotia contributed by the few diseased lettuce plants were offset by the significant reductions in the number of sclerotia by the broccoli residue. Spatial patterns of disease incidence reflected the pattern of inoculum distribution in the soil at the Hartnell site. Higher inoculum density coupled with an aggregated distribution was associated with an aggregation in disease incidence. At Spence, this correlation was poor in most seasons because of progressive decline in the lettuce drop incidence and lack of treatment differences. In greenhouse experiments, the competence volume for S. minor sclerotia was quantified, which was calculated to be 25 for 100% infection and 200 cm for 50% infection. Thus, in 100 cm of soil, a minimum of four to five sclerotia are needed for 100% of infection, explaining the high correlation between inoculum density and disease incidence.
1995年至1998年期间，在两个地点进行了田间试验，以确定小核盘菌的种群动态和生菜菌核病的发病率。在接种物密度较低（每100平方厘米土壤中<7个菌核）且随机分布的斯彭斯试验点，轮作处理包括：连作生菜（LLL）、生菜与西兰花轮作（LBL）以及生菜后接休耕期（LFL）。在接种物密度较高（每100平方厘米土壤中>7个菌核）且均匀分布的哈特内尔试验点，处理包括：连作生菜（LLLL）、西兰花和生菜交替种植（BLBL）、连作西兰花或生菜（BBLL）以及休耕-生菜-休耕-生菜（FLFL）。在哈特内尔试验点连作生菜（LLLL）的情况下，尽管初始接种物密度分布均匀，但接种物分布逐渐形成聚集的空间格局。在休耕处理（FLFL）中，生菜种植后空间格局趋于聚集，休耕时聚集程度较低或呈随机分布。与这两种处理不同的是，涉及与西兰花轮作的处理（BLBL和BBLL）无论田间种植何种作物，接种物始终呈现随机的空间格局。少数染病生菜植株产生的菌核数量的边际增加被西兰花残体导致的菌核数量显著减少所抵消。病害发病率的空间格局反映了哈特内尔试验点土壤中接种物的分布格局。较高的接种物密度加上聚集分布与病害发病率的聚集相关。在斯彭斯试验点，由于生菜菌核病发病率逐渐下降且处理间差异不明显，在大多数季节这种相关性较差。在温室试验中，对小核盘菌菌核的侵染有效体积进行了量化，计算得出100%侵染时为25立方厘米，50%侵染时为200立方厘米。因此，在100平方厘米的土壤中，100%侵染至少需要4至5个菌核，这解释了接种物密度与病害发病率之间的高度相关性。
