麦瓶草种群中的花药黑粉菌感染:花的形态学变异、菌孢子散布式样及病原菌-传媒调节性选择

摘要

The anther-smut Microbotryum violaceum (Brandenburger and Schvinn) G. Deml. And Oberw.) causes a systemic infection of its host Silene dioica (L.) Clairv., resulting in sterility and production of teliospores (dispersal propagules) in flowers. These spores are transmitted to healthy plants mainly by flower visitors. The behavioral responses of flower visitors to a variation in floral characters, are not only likely to affect rates of pollen export/import, but also the rate of spore deposition and probability of disease. In a transplantation experiment, using plants from four different populations, we tested for correlation between variation in female floral morphology and patterns of spore and pollen deposition, and a resulting risk of disease. The source populations in this experiment were located on four islands in Skeppsvik archipelago in northern Sweden, and represented a gradient of disease incidence from completely healthy (Island 1), low incidence (Island 2) to high incidences (Islands 3 and 4) of disease. Fifty plants from each population were transplanted to the center of the population on Island 4. There were significant differences among the transplants in floral characters, I.e. Corolla size, style length and ovule number. Plants from the non-diseased population had larger flowers and longer styles than plants from the highly diseased populations. Numbers of pollen grains and spores deposited on flowers were strongly and positively correlated. We found that plants originating from the non-diseased population captured approximately 4 times more pollen and 9 times more spores per flower than the individuals from the resident population (Island 4, population 4). The incidences of disease among plants from the four populations differed significantly, and was 37%, 20%, 18% and 0 for populations 1, 2, 3 and 4 respectively. In a survey of ten populations we found a significant negative correlation between the mean style length (positively correlated with corolla size and ovule number) among healthy plants and incidence of disease in these populations. The potentiality for pathogen-pollinator mediated selection on floral characters and consequences for gene flow between populations of Silene dioica are discussed.%花药黑粉菌(Microbotryum violaceum)可系统侵染其寄主植物麦瓶草(Silene dioica),使其不育而代之以在植物花中布满菌孢子.这些菌孢子主要由花传媒昆虫带到健康植株.花传媒昆虫对花部特征变异的行为反应不仅可能影响花粉的输入/输出率,而且影响菌孢子的着落率和植株的发病与否.为研究S.dioica雌株花部性状特征与花粉传布、菌孢子着落及由此而导致的植株染病之间的相关性,用采自4个不同S.dioica种群的植物进行了移栽实验.该4个种群均位于瑞典北部的Skeppsvik群岛,代表了从健康(岛1,种群1),低度发病(岛2,种群2)到高度发病(岛3、4,种群3、4)的发病梯度.从上述4个不同种群中各采50个植株移栽至岛4的中部.来自健康种群的植株较来自高发病种群的植株具有较大的花,较长的花柱.研究发现,着落在花上的花粉粒数和菌孢子数呈强正相关.来自健康种群的植株每朵花上着落的花粉粒和菌孢子数分别是高发病种群(种群4)植株的4倍和9倍,导致来自4个不同种群的植株的发病率存在着显著差异,种群1、2、3、4的发病率分别为37%、20%、18%、0.在涉及10个种群的田间调查研究中,发现种群中健康植株的平均花柱长度(与花冠大小,胚珠数目正相关)与植株的发病率显著负相关.讨论了病原体-传媒调节的植物花部性状特征选择潜势及由其导致的麦瓶草S. dioica种群间的基因漂移.