Emergence dynamics of Chinese sprangletop (Leptochloa chinensis (L.) Nees.) in wet direct-seeded lowland rice

Chinese sprangletop (Leptochloa chinensis (L.) Nees.) is a C4 grass that closely resembles rice at the seedling stage, often leading to delayed identification and significant yield losses. Understanding the conditions that favour emergence and survival is essential for characterising its growth dynamics in humid tropical systems; accordingly, seed germination was evaluated under a range of environmental stresses. Germination studies were conducted under laboratory conditions and as pot culture experiments at the College of Agriculture, Vellayani, which experiences a humid tropical climate. Although light triggered germination, it was not identified as an essential requirement for seedling emergence. The highest cumulative germination (87 %) occurred at a fluctuating temperature regime of 25/15 °C, indicating that alternating temperatures can favour germination of buried seeds of L. chinensis. The emergence pattern of the seed and rhizome differed markedly. Seeds exhibited higher emergence when placed on the soil surface and showed limited ability to emerge from deeper layers. In contrast, emergence from rhizomatous underground stems bearing nodal roots was observed up to a depth of 4 cm, but not beyond. Higher seed germination immediately after maturity (87 %) suggests options for soil seed bank management, with implications for stale seedbed techniques involving propagule exposure followed by shallow tillage for crop establishment. Seeds were observed to retain viability under prolonged flooding, with 45 % germination even after 30 days, demonstrating the resilient nature of the weed. However, aerobic conditions with alternate irrigation promoted higher germination (70 %) and establishment, suggesting that mild moisture fluctuations can trigger emergence, ascribing its dominance in direct-seeded rice systems. Continuous flooding or maintaining a shallow water layer substantially suppressed germination and emergence. The study identified deep seed burial and continuous flooding as factors that could limit the germination and establishment of L. chinensis in wetland rice.