Data from: Surveying the spatial distribution of feral sorghum (Sorghum bicolor L.) and its sympatry with johnsongrass (S. halepense) in South Texas

Sorghum (Sorghum bicolor) is an important grain and forage crop grown across the US. In some areas, sorghum can become feral along roadsides and other ruderal areas, as a result of seed spill during harvest or transport. In some of these situations, feral sorghum grows in or near established johnsongrass (S. halepense) populations. Johnsongrass, a wild relative of sorghum and an incredibly noxious weed, is capable of hybridizing with cultivated sorghum. Because commercial hybrid sorghum cultivars are produced with cytoplasmic male sterility, progeny of the hybrid crop which compose the founder feral populations also segregate for male sterility. Consequently, male sterility in feral sorghum may increase the risk of outcrossing with johnsongrass. Using field surveys and spatial modelling, the present study aimed at documenting the occurrence of feral sorghum and understanding the anthropogenic and environmental factors that influence its distribution. Further, this research documented the sympatry of feral sorghum and johnsongrass in the roadside habitat. A total of 2077 sites were visited during a systematic field survey conducted in fall 2014 in South Texas. Feral sorghum and johnsongrass were found in 360 and 939 sites, while the species co-existed at 48 sites (2.3% of all surveyed sites). The binary logistic analysis showed a significant association between the presence of feral sorghum and road type, road body-type, micro-topography of the sampling site, nearby land use, and the presence of johnsongrass, but no association with the distance to the nearest grain sorting facility. The probability of finding feral sorghum away from johnsongrass patches was generally higher than finding them co-occur in the same location. A probability map for spatial distribution of feral sorghum was developed using the nearby land use type and the regional habitat suitability for johnsongrass as two key predictors. Overall, results show that feral sorghum and johnsongrass co-occur at low frequencies in the roadside habitats of South Texas, but these low levels still present a significant opportunity for hybridization between the two species outside of cultivated fields.高粱（Sorghum bicolor）是美国广泛种植的重要粮饲兼用作物。在部分区域，由于收获或运输过程中种子散落，高粱可在路边及其他荒地区域逸生为野生种群。在部分此类场景中，逸生高粱会生长在已建立的约翰逊草（S. halepense）种群中或其附近。约翰逊草是高粱的野生近缘种，同时也是极具危害性的恶性杂草，可与栽培高粱发生杂交。由于商业化杂交高粱品种是通过细胞质雄性不育（cytoplasmic male sterility）系统繁育的，作为逸生种群创始群体的杂交作物后代同样会发生雄性不育性状分离。因此，逸生高粱的雄性不育特性可能提升其与约翰逊草发生异交的风险。本研究通过野外调查与空间建模（spatial modelling），旨在记录逸生高粱的发生情况，并解析影响其分布的人为与环境因子。此外，本研究还调查了路边生境中逸生高粱与约翰逊草的同域分布（sympatry）情况。2014年秋季，研究团队在南德克萨斯州开展系统性野外调查，共走访2077个样点。其中，逸生高粱和约翰逊草分别在360个和939个样点中被发现，两物种共存在48个样点中，占所有调查样点的2.3%。二元逻辑回归（binary logistic analysis）分析结果显示，逸生高粱的存在与道路类型、道路断面类型、样点微地形、周边土地利用类型以及约翰逊草的存在情况存在显著关联，但与距最近谷物分选设施的距离无显著关联。相较于两物种同域分布的样点，在远离约翰逊草斑块的区域发现逸生高粱的概率普遍更高。研究以周边土地利用类型和约翰逊草的区域生境适宜性作为两个关键预测因子，构建了逸生高粱空间分布的概率预测图。总体而言，研究结果表明，在南德克萨斯州的路边生境中，逸生高粱与约翰逊草的同域发生频率较低，但即便如此，这一低频率仍为两物种在栽培田块之外发生杂交提供了显著的潜在机会。