Seed germination ecology of Echinochloa glabrescens and its implication for management in rice (Oryza sativa)

Echinochloa glabrescens is a C4 grass weed that is very competitive with rice when left uncontrolled. The competitive ability of weeds is intensified in direct-seeded rice production systems. A better understanding is needed of factors affecting weed seed germination, which can be used as a component of integrated weed management in direct-seeded rice. This study was conducted to determine the effects of temperature, light, salt and osmotic stress, burial depth, crop residue, time and depth of flooding, and herbicide application on the emergence, survival, and growth of two populations [Nueva Ecija (NE) and Los Banos (IR)] of E. glabrescens. Seeds from both populations germinated at all temperatures. The NE population had a higher germination rate (88%) from light stimulation than did the IR population (34%). The salt concentration and osmotic potential required to inhibit 50% of germination were 313 mM and -0.24 MPa, respectively, for the NE population and 254 mM and -0.33 MPa, respectively, for the IR population. Emergence in the NE population was totally inhibited at 4-cm burial depth in the soil, whereas that of the IR population was inhibited at 8 cm. Compared with zero residue, the addition of 5 t ha-1 of rice residue reduced emergence in the NE and IR populations by 38% and 9%, respectively. Early flooding (within 2 days after sowing) at 2-cm depth reduced shoot growth by 50% compared with non-flooded conditions. Pretilachlor applied at 0.075 kg ai ha-1 followed by shallow flooding (2-cm depth) reduced seedling emergence by 94 to 96% compared with the nontreated flooded treatment. Application of postemergence herbicides at 4-leaf stage provided 85 to 100% control in both populations. Results suggest that integration of different strategies may enable sustainable management of this weed and of weeds with similar germination responses.

Echinochloa glabrescens（无毛稗）是一种C4草本杂草，在未实施防控的情况下与水稻的竞争性极强。在直播稻种植体系中，该杂草的竞争能力会进一步增强。亟需深入解析影响杂草种子萌发的各类因素，此类信息可作为直播稻杂草综合管理体系的组成部分。本研究旨在探究温度、光照、盐胁迫、渗透胁迫、埋土深度、作物残体、淹水时长与淹水深度，以及除草剂施用对无毛稗两个种群——新怡惹拉（Nueva Ecija，简称NE）与洛斯巴尼奥斯（Los Banos，简称IR）——的出苗、存活与生长的影响。两个种群的种子均可在所有测试温度下萌发。经光照刺激后，NE种群的发芽率（88%）显著高于IR种群（34%）。抑制NE种群50%萌发所需的盐浓度与渗透势分别为313 mM与-0.24 MPa，IR种群对应的抑制参数则分别为254 mM与-0.33 MPa。当土壤埋土深度达4 cm时，NE种群的出苗完全被抑制；而IR种群的出苗抑制则发生在埋土深度8 cm处。与无残体处理组相比，施加5吨·公顷⁻¹的水稻残体可分别使NE与IR种群的出苗率降低38%与9%。相较于未淹水对照，播后2天内进行2 cm深度的早期淹水处理，可使植株地上部生长量降低50%。以每公顷0.075千克有效成分的剂量施用丙草胺（pretilachlor）后，辅以2 cm深度的浅淹水处理，相较于未施药的淹水对照组，可使幼苗出苗率降低94%~96%。在四叶期施用苗后除草剂，可使两个种群的杂草防效达到85%~100%。研究结果表明，整合多种防控策略，可实现该杂草以及萌发响应特征相似的杂草的可持续防控。