Ryegrass (Lolium spp.) is a troublesome weed in major wheat (Triticum aestivum L.) production regions in the United States. High diversity and adaptive potential are known to contribute to its success as a weed species and also create difficulties in correct species identification in fields. The objective of this research was to characterize diversity for 16 different morphological traits among 56 Lolium populations collected from wheat production fields across the Texas Blackland Prairies region and identify Lolium species based on taxonomic characteristics. Populations were highly diverse (both at inter- and intrapopulation levels) for the traits studied, and a taxonomic comparison with USDA-GRIN reference samples revealed that all the populations were variants of Italian ryegrass [Lolium perenne L. ssp. multiflorum (Lam.) Husnot] with a few offtypes of perennial ryegrass (Lolium perenne L.) or probable hybrids between the two species. Hierarchical clustering grouped the populations into six clusters based on their similarities for the morphological traits investigated. Principal component analysis showed that the variability for yield traits greatly contributed to the total diversity. Pre-flowering plant height (stage 10 on Feekes scale) was positively correlated with tiller count, shoot biomass, and spike count, but not with total seed count per plant, whereas plant height at maturity (stage 11.3 to 11.4 on Feekes scale) was highly correlated with total seeds per plant. Further, basal node color was positively correlated with plant growth habit, regrowth rate, and leaf color. Leaf blade width was positively correlated with survival to pinoxaden and multiple herbicides, whereas, spike count was negatively correlated with survival to mesosulfuron. The high levels of intra- as well as interpopulation variability documented in this study indicate the potential of this species to rapidly adapt to herbicides and emphasize the need for implementing diverse management tactics, including the integration of harvest weed seed control.

中文翻译：

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德克萨斯黑地大草原黑麦草（黑麦草属）种群的物种鉴定和形态特征多样性评估

黑麦草 (黑麦草spp.) 是主要小麦 (小麦L.) 美国的生产地区。众所周知，高度的多样性和适应潜力有助于其作为杂草物种的成功，并且也为在田间正确识别物种造成困难。本研究的目的是描述 56 种不同形态特征的多样性。黑麦草从德克萨斯州黑地大草原地区的小麦生产田收集的种群并确定黑麦草基于分类特征的物种。对于所研究的性状，种群高度多样化（种群间和种群内水平），与 USDA-GRIN 参考样本的分类比较显示所有种群都是意大利黑麦草的变种 [黑麦草L. ssp。何首乌(Lam.) Husnot] 与一些多年生黑麦草 (黑麦草L.) 或两个物种之间可能的杂交种。层次聚类根据所研究的形态特征的相似性将种群分为六个集群。主成分分析表明，产量性状的变异性对总多样性有很大贡献。开花前的植物高度（Feekes 等级的第 10 阶段）与分蘖数、枝条生物量和穗数呈正相关，但与每株植物的种子总数无关，而成熟时的植物高度（Feekes 等级的 11.3 至 11.4 阶段）是与单株种子总数高度相关。此外，基部颜色与植物生长习性、再生率和叶色呈正相关。叶片宽度与对敌草胺和多种除草剂的存活率呈正相关，而 尖峰计数与甲磺隆的存活率呈负相关。本研究记录的高水平的种群内和种群间变异性表明该物种具有快速适应除草剂的潜力，并强调需要实施多种管理策略，包括整合收获杂草种子控制。