Abstract
Saccharum spontaneum L. is an invasive grass that has spread extensively in disturbed areas throughout the Panama Canal watershed (PCW), where it has created a fire hazard and inhibited reforestation efforts. Currently physical removal of aboveground biomass is the primary means of controlling this weed, which is largely ineffective and does little to inhibit spread of the species. Little is known about reproduction of this species, although it is both rhizomatous and produces abundant seed. Here we report a series of studies looking at some of the basic reproductive mechanisms and strategies utilised by S. spontaneum to provide information to support development of better targeted management strategies.We found that seed produced between September and November was germinable both in the lab and in situ. Genetic diversity of mature stands was assessed using microsatellite markers and found to be high, even at small scales. Studies of vegetative reproduction showed that buds on stems that had been dried for up to six weeks were still capable of sprouting. Separate experiments showed that stem fragments could sprout when left on the surface or buried shallowly and that larger pieces sprouted more readily than smaller pieces.Collectively these results demonstrate that S. spontaneum in the PCW has the capability to produce many propagules that can successfully recruit and it is likely that seed dispersal drives the spread of the species. Timing of management actions to reduce flowering would significantly reduce the seed load into the environment and help to prevent spread to new sites. Similarly, where biomass is cut, cutting stems into smaller pieces will allow the stems to dry out and reduce the ability of buds to sprout. Additionally, attention should be paid to prevent accidental transport to new sites on machinery.
Highlights
Many of the “World’s Worst Weeds” are perennial species with the ability to spread with both seeds and vegetative structures (Holm et al 1977) and perennial grasses are notorious invaders of both agricultural and natural areas (D’Antonio and Vitousek 1992)
To examine if the patterns we found at these sites were consistent across large stands, we sampled parallel transects separated by 20 m at two independent stands in Soberania National Park within an area dominated by S. spontaneum (Sites 5 and 6, Fig. 1, Appendix 1; see Saltonstall and Bonnett 2012 for a description of the stands)
Flowering across the landscape is extensive and our results suggest that seed dispersal clearly plays a major role in this spread
Summary
Many of the “World’s Worst Weeds” are perennial species with the ability to spread with both seeds and vegetative structures (Holm et al 1977) and perennial grasses are notorious invaders of both agricultural and natural areas (D’Antonio and Vitousek 1992). It is a highly adaptable polyploid that grows in a wide range of habitats across southern Asia and east Africa to the Mediterranean, spanning the tropics to temperate regions from latitudes 8° S to 40° N (Daniels and Roach 1987; Tai and Miller 2001) It is both wind-pollinated and -dispersed, it reproduces vegetatively, through clonal spread either from underground rhizomes or culm fragments. Because of S. spontaneum’s potential to propagate via seeds and its propensity for aggressive rhizomatous spread, it is considered a weed, even in countries to which it is native such as India (Panje 1970, Yadav et al 2007) and Thailand (Pichitkul 2009) It has been introduced into other countries for use in sugarcane breeding programs (Bonnett et al 2008) and is considered a noxious weed in many countries including the USA (USDA 2010). In India, flowering is initiated at the end of the rainy season, with diurnal variations in humidity and temperature likely influencing both pollen and seed dispersal (Panje and Srinivisan 1959)
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