恶性入侵植物豚草的繁育系统特性

Breeding system of a noxious invasive alien plant,Ambrosia artemisiifolia L.

豚草(Ambrosia artemisiifolia L.)是原产于北美的一年生恶性入侵植物,目前已广泛分布在我国东北、华北、华中和华东等地,威胁农业、生态和民众健康。该种雌、雄头状花序同株,以种子繁殖,因而其有性繁殖特性对其扩散和爆发具有重要影响。运用套袋授粉和联苯胺-过氧化氢法等实验方法,对入侵江苏常熟的豚草种群的繁育系统特性进行了研究。结果表明,豚草花粉活力在开花后第4天开始出现,第8天到第10天花粉活力比较高;柱头可授性在开花第2天开始出现,第5天到第8天柱头可授性较高;同植株上同一时期开花的雌花的柱头可授性和雄花的花粉活力有5d左右的重叠期。不套袋处理(自然条件)和异株授粉处理下,豚草的结实率都比较高,分别达48.4%和44.4%,两者间无显著差异(P>0.05);而同株授粉处理的结实率较低,仅3.4%,极显著低于不套袋处理和异株授粉的结实率(P<0.01)但显著大于0(P<0.05)。分析表明,豚草属于自交不亲和种,但又可部分自交亲和,不具有无融合生殖特性。因此,对在新分布区的零星豚草植株进行及时防除,将取得事半功倍的效果。

Ragweed （Ambrosia artemisiifolia L. ）, a member of the Asteraceae （ Compositae）, to North America. The species is a noxious invasive plant worldwide, with infestation by is an annual species native ragweed frequently posing challenges to protection and functioning of local ecosystems, crop production in agricultural areas, and public health. In North America, Europe, and Australia, ragweed is a major nuisance in arable areas and other habitats. At present, ragweed is relatively rare in agricultural areas of China compared with corresponding regions of other countries; nevertheless, the species is broadly distributed throughout many regions of China, including 21 of 34 provinces. Because ragweed is a monoecious annual that reproduces with high fecundity via seeds, its mating patterns may be closely related to its invasiveness and dissemination ability. In China, alien invasive plants in the family Asteraceae that are characterized by high fecundity tend to retain a high potential for self-compatibility, while many self-incompatible invasive alien plant species are perennials with high vegetative reproduction ability. Although ragweed does not reproduce vegetatively, its breeding system has not been fully elucidated. Some studies have indicated that ragweed can readily generate mature seeds autogamously and allogamously, whereas other experimental evidence implies that this species is self-incompatible. To shed further light on the breeding system of ragweed, we transplanted plants from an invasive ragweed population in Changshu, Jiangsu Province, China, and used them in a series of common garden experiments. We studied patterns of pollen viability and stigma receptivity. We also investigated the ragweed breeding system and apomixis by measuring seed sets of different individual plants subjected to four different treatments： self-pollination, cross-pollination, open-pollination, and bagging of female capitula. Viable ragweed pollen was first detected four days after flowering, with viability peaking eight to ten days post-anthesis. Viable stigmas were observed on the second day, with viable levels reaching a maximum five to eight days after flowering. The overlapping period of pollen viability and stigma receptivity was thus about five days. Seed set of ragweed individuals was highest under open-pollination （48.4%, on average） and cross-pollination （44.4%, on average） treatments, although the difference between these two treatments was not significant （P 〉 0.05）. Seed set of self-pollinated individuals was much significantly lower （ P 〈 0.01 ） than values obtained under open pollination and cross pollination, but the average value, 3.4%, was significantly higher than zero （ P 〈 0.05）. In addition, no seed set was observed from female capitula. Taken together, our results suggest that compatibility and no apomictic ability. Over the long run, bagged ragweed is mainly self-incompatible, but possesses slight self- self-incompatibility enhances ragweed diversity and adaptation to newly invaded areas; initially, however, this characteristic does not promote its spread, as it is obviously difficult for a few individual ragweed plants to form a large population via seeds relying solely on hybridization. Self-incompatibility may thus be one of the major reasons why ragweed seldom infests small croplands subjected to intensive weed management practices. Consequently, removal of sporadic individuals from new ragweed distributional areas should be made a priority to prevent serious invasion.