The distribution of genetic diversity in invasive plant populations can have important management implications. Alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] was introduced into the United States around 1900 and has since spread throughout much of the southern United States and California. A successful biological control program was initiated in the late 1960s that reduced A. philoxeroides in the southern United States, although control has varied geographically. The degree to which variation among genotypes may be responsible for variation in control efficacy has not been well studied due to a lack of genetic data. We sampled 373 plants from 90 sites across the United States and genotyped all samples at three chloroplast regions to help inform future management efforts. Consistent with clonal spread, there was high differentiation between sites, yet we found six haplotypes and high haplotype diversity (mean h = 0.48) across states, suggesting this plant has been introduced multiple times. Two of the haplotypes correspond to previously described biotypes that differ in their susceptibility to herbicides and herbivory. The geographic distribution of the three common haplotypes varied by latitude and longitude, while the other haplotypes were widespread or localized to one or a few sites. All the haplotypes we screened are hexaploid (6n = 102), which may enhance biological control. Future studies can use these genetic data to determine whether genotypes differ in their invasiveness or respond differently to control measures. Some states, for instance, have mainly a single haplotype that may respond more uniformly to a single control strategy, whereas other states may require a variety of control strategies. These data will also provide the basis for identifying the source regions in South America, which may lead to the discovery of new biological control agents more closely matched to particular genotypes.

中文翻译：

---

美国克隆水草空心莲子草的高遗传多样性

入侵植物种群中遗传多样性的分布可能具有重要的管理意义。鳄鱼草 [空心莲子草(Mart.) Griseb.] 于 1900 年左右被引入美国，此后传播到美国南部和加利福尼亚的大部分地区。1960 年代后期启动了一项成功的生物控制计划，该计划减少了空心莲子在美国南部，尽管控制在地理上有所不同。由于缺乏遗传数据，基因型之间的变异可能导致控制效果变异的程度尚未得到很好的研究。我们从美国 90 个地点对 373 株植物进行了采样，并对三个叶绿体区域的所有样本进行了基因分型，以帮助为未来的管理工作提供信息。与克隆传播一致，位点之间存在高度分化，但我们发现了六种单倍型和高单倍型多样性（平均H= 0.48) 跨州，表明该工厂已被多次引入。其中两种单倍型对应于先前描述的生物型，它们对除草剂和食草动物的敏感性不同。三种常见单倍型的地理分布因纬度和经度而异，而其他单倍型广泛分布或局限于一个或几个地点。我们筛选的所有单倍体都是六倍体（6n= 102），这可能会增强生物控制。未来的研究可以使用这些遗传数据来确定基因型的侵袭性是否不同或对控制措施的反应是否不同。例如，一些州主要具有单一的单倍型，可能更一致地响应单一的控制策略，而其他州可能需要多种控制策略。这些数据还将为确定南美洲的来源地区提供基础，这可能会导致发现与特定基因型更匹配的新生物控制剂。