Bucheli Erika, Shykoff Jacqui A
Experimental Ecology, Swiss Federal Institute of Technology, ETHZ-NW, CH-8092 Zürich, Switzerland, , , , , , CH.
Oecologia. 1999 Apr;119(1):55-62. doi: 10.1007/s004420050760.
The anther smut fungus Microbotryum violaceum is a pollinator-transmitted plant disease. As for other vector-borne diseases, frequency-dependent transmission patterns are predicted, in contrast to the density-dependent transmission of passively spread diseases. Frequency dependence will, however, only arise if vectors compensate for varying plant spacings. To test this assumption, we set up experimental populations of the host plant, Silene latifolia, with varying disease density (number of diseased plants per plot) and frequency (proportion of plants diseased), and three different plant spacings. We measured spore deposition on healthy flowers in these plots on two dates. Spore deposition decreased considerably from the first to the second census, perhaps related to the concomitant decrease in inflorescence sizes of diseased plants. At our first census, spore deposition rates varied with disease frequency, and the effect of frequency depended on plant spacing. While spore deposition was positively frequency dependent at the 1.5-m inter-plant spacing, no effect of disease frequency was found at a spacings of 0.5 m or 3 m. Nor was there an effect of disease density on spore deposition at the first census. At the later census, on the other hand, spore deposition increased almost significantly with increasing disease density (P = 0.08). This difference in deposition pattern together with a significant decrease in spore receipt indicates changes in pollinator spectrum and/or activity. The correlation of spore numbers among flowers within plants, an indication for intra-plant moves by vectors, was significant at 0.5 m and 1.5 m but not at 3 m. Floral traits and sex of individual plants influenced the number of spores they received. On the first census date, spore deposition increased with increasing inflorescence size in female but not in male plants. On the second census date, neither sex nor number of open flowers had an effect on spore receipt. None of the experimental plants became infected, however, probably because of the unusually hot and dry weather.
花药黑粉菌（Microbotryum violaceum）是一种通过传粉者传播的植物病害。与其他媒介传播的疾病一样，预计其传播模式为频率依赖型，这与被动传播疾病的密度依赖型传播形成对比。然而，只有当媒介能够补偿不同的植物间距时，才会出现频率依赖性。为了验证这一假设，我们建立了不同疾病密度（每块地患病植物的数量）和频率（患病植物的比例）以及三种不同植物间距的寄主植物宽叶蝇子草（Silene latifolia）实验种群。我们在两个日期测量了这些地块中健康花朵上的孢子沉积量。从第一次普查到第二次普查，孢子沉积量大幅下降，这可能与患病植物花序大小的相应减少有关。在我们的第一次普查中，孢子沉积率随疾病频率而变化，频率的影响取决于植物间距。在植株间距为1.5米时，孢子沉积呈正频率依赖性，而在0.5米或3米的间距下，未发现疾病频率有影响。在第一次普查时，疾病密度对孢子沉积也没有影响。另一方面，在后期普查中，孢子沉积量几乎随着疾病密度的增加而显著增加（P = 0.08）。这种沉积模式的差异以及孢子接收量的显著减少表明传粉者谱和/或活动发生了变化。植物内花朵间孢子数量的相关性，即媒介在植物内移动的一个指标，在0.5米和1.5米时显著，但在3米时不显著。个体植物的花部特征和性别影响它们接收的孢子数量。在第一次普查日期，雌性植物的孢子沉积量随着花序大小的增加而增加，而雄性植物则不然。在第二次普查日期，性别和开放花朵的数量对孢子接收均无影响。然而，没有一株实验植物被感染，可能是因为天气异常炎热干燥。
