Germination biology of three populations of Navua sedge (Cyperus aromaticus)

Abstract

Navua sedge [Cyperus aromaticus (Ridley) Mattf. & Kük.] is an aggressive perennial sedge native to equatorial Africa which has become problematic in many Pacific islands and wet tropical Queensland, Australia. It has had a significant impact on livestock grazing industry, sugarcane (Saccharum officinarum L.) and banana (Musa acuminata Colla) plantations and various other ecosystems. A laboratory-based research investigation was conducted to understand germination and emergence requirements under various environmental conditions, of three geographically varied populations sourced from South Johnstone (SJ), Mackay (M) and Nyleta Creek (NC) in Queensland. Germination was identified to be stimulated by light with no germination recorded under darkness. Populations SJ and NC had optimal germination at alternating temperatures of 25/15, 30/20 and 35/25 C whereas population M had optimal germination at 25/15 and 30/20 C. All populations recorded over 85% germination in all pH levels tested. Seeds of population SJ was more sensitive to salinity compared to populations M and NC, with SJ showing no germination at 100 mM whereas populations M and NC had 23% and 9% germination, respectively. An inverse relationship was observed between osmotic potential and germination, with no germination recorded at osmotic potentials below -0.8 MPa in any population indicating moisture availability is a critical requirement for germination. Exposing seeds to 120 C radiant heat completely inhibited germination in populations M and NC, whereas 3% of population SJ germinated following a 180 s exposure at 120 C. Seedling emergence decreased as planting depth increased. Emergence was greatest for seeds on the soil surface or at 0.5 cm burial depth, consistent with germination being stimulated by light. Knowledge of these biological characteristics of C. aromaticus seed germination will assist in investigation of suitable control actions for this species particularly in the early stage of its invasion into new areas, and contribute to significant reduction in the soil-stored seed bank.

Biology, Ecology and Management of the Invasive Navua Sedge (Cyperus aromaticus)—A Global Review

“…It possesses a robust perennial, creeping rhizome and densely set culms (stems). It has a continuously growing underground stem (rhizome) that produces shoots at regular intervals along its length [ 6 , 10 ]. The rhizome possesses scales about 5 mm thick, pale brown to dark purple or blackish, and less than 10 mm long ( Figure 1 c) [ 10 , 24 ].…”

“…Navua sedge can be found along roadsides, railways, lawns, grassland, wastelands, grazed pastures, construction sites, creek banks and forests ( Figure 2 ). Navua sedge is a perennial monocot, producing flowers and seeds throughout the year, and the seeds can also germinate at a range of temperatures, soil moisture, pH levels, salinity, radiant heat treatment, osmotic potential and light intensity [ 6 ]. It can be found in all types of soils, including black, sandy, alkaline and clay soils, but it is noted that seedling emergence decreases with increased seed burial depth [ 6 ].…”

“…& Kukenth) is native to equatorial African, the Seychelles, Mauritius and Madagascar and has been declared as a weed in Singapore and several island nations of the Pacific including French Polynesia and Fiji [ 1 , 2 , 3 ]. Since its introduction in the 1970s into the wet tropical regions of northern Queensland in Australia [ 4 , 5 ], Navua sedge has become an aggressive perennial, causing negative impacts in the beef, dairy and cropping industries [ 4 , 5 , 6 ]. It has spread along many roadsides and into grazing pastures across the wet tropics in northern Queensland.…”

“…It has spread along many roadsides and into grazing pastures across the wet tropics in northern Queensland. In this latter respect, Navua sedge has a low nutrient value and, as a consequence, cattle do not like to feed on them, thus contributing to its unfettered spread [ 6 , 7 ]. Navua sedge has been recognised as a problematic invasive weed for decades in pastures, roadsides, lawns, and crops, including banana ( Musa acuminata Colla), sweet potato ( Ipomoea batatas L.) and sugarcane ( Saccharum officinarum L.) farms of wet tropical areas within Australia [ 6 ].…”

“…Currently, mechanical and chemical control options are mainly used to manage Navua sedge in Australia and Fiji [ 4 , 5 , 6 ]. However, it has been found that these approaches are not sustainable due to short-term effectiveness and adverse impacts to the environment of the management tactics.…”