Kenneth R. Woodard

Regional performance of tall tropical bunchgrasses in the Southeastern U.S.A.

Abstract This paper contains results of four research projects conducted over a five-year period (1986–1990), to evaluate high yielding perennial bunchgrasses as a renewable energy source. In peninsular Florida, tall bunchgrasses including elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.), have produced far greater annual dry biomass (DB) yields than forage and sweet sorghums (Sorghum bicolor (L.) Moench). In the colder locations in Floridas panhandle and at Auburn, Alabama, adapted elephantgrass and energycane genotypes produced comparable-to-much larger DB yields than the annual sorghums. A long near-linear period of DB accumulation, lasting 140 to 196 days, was responsible for the high yielding ability of the perennial bunchgrasses. However, the daily rate of DB accumulation of the bunchgrasses and the efficiency by which incoming solar energy was converted to chemical energy in plant biomass, were not unlike those of other C-4 grasses during active growth. The biomass of elephantgrass and energycane can be stored easily by ensiling because harvested herbage (before ensiling) has a low buffering capacity. Propagation quality of elephantgrass stems can be improved by applying high rates of fertilization to nursery plants.

Management of Perennial Warm-Season Bioenergy Grasses. II. Seasonal Differences in Elephantgrass and Energycane Morphological Characteristics Affect Responses to Harvest Frequency and Timing

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp. interspecific hybrid) are perennial C4 grasses with potential for use as bioenergy feedstocks. Their biomass production has been quantified, but differences in plant morphology and the relationship of morphology with biomass harvested and plant persistence are not well understood. The objective was to quantify monthly changes in morphological characteristics of elephantgrass (cv. Merkeron and breeding line UF1) and energycane (cv. L 79-1002) and relate these changes to biomass accumulation and plant responses to defoliation. All were evaluated monthly during full-season growth or when defoliated once in mid-season. Merkeron and UF1 elephantgrass generally showed similar morphological characteristics. Relative to energycane, elephantgrass had fewer tillers early in the growing season, less seasonal variation in tiller number, greater tiller mass and maximum leaf area index (LAI), and earlier spring development of LAI. Energycane showed slower leaf area development in spring, lower maximum LAI, and shorter period of increasing tiller mass and canopy height during the growing season relative to UF1. Elephantgrass had greater incidence of lodging than energycane when exposed to high wind, likely due to greater elephantgrass tiller mass. Morphological characteristics of tall-growing bioenergy grasses help to explain differences among them in biomass production and plant persistence responses to defoliation.

Genetic Diversity of Biofuel and Naturalized Napiergrass (Pennisetum purpureum)

Abstract Biofuel crops such as napiergrass possess traits characteristic of invasive plant species, raising concern that biofuels might escape cultivation and invade surrounding agricultural and natural areas. Napiergrass biofuel types are being developed to have reduced invasion risk, but these might be cultivated in areas where naturalized populations of this species are already present. The successful management of napiergrass biofuel plantations will therefore require techniques to monitor for escaped biofuels as distinguished from existing naturalized populations. Here we used 20 microsatellite DNA markers developed for pearl millet to genotype 16 entries of napiergrass, including naturalized populations and accessions selected for biofuel traits. Use of the markers showed a clear genetic separation between the biofuel types and naturalized entries and revealed naturalized populations undergoing genetic isolation by distance. These findings demonstrated the utility of microsatellite marker transfer in the development of an important tool for managing the invasion risk of a potential biofuel crop. Nomenclature: Napiergrass, Pennisetum purpureum Schumach., pearl millet, Pennisetum glaucum (L.) R. Br. Management Implications: Cellulosic biofuels offer opportunities for sustainable energy production, but many traits of biofuel crop species increase the potential for escape and invasion into surrounding natural areas. Biofuel crop accessions might be selected for high biomass and reduced invasion risk, but management of biofuel plantings will nevertheless require a means to monitor for the escape of cultivated varieties, especially in areas where naturalized populations of the same species are also present. DNA microsatellite markers offer technical and practical advantages for this purpose, including marker transferability. Markers that have already been developed for a crop or model species can be transferred to a related species, sparing the time and cost of marker development. Napiergrass (Pennisetum purpureum) is a crop that has tremendous potential for biofuel production in areas where naturalized populations are already present and creating weed problems. Exploiting napiergrass as a biofuel will require risk management strategies that include a means to genetically track both the cultivated and naturalized types. We found that microsatellite markers developed for pearl millet (Pennisetum glaucum) readily distinguished the naturalized populations of napiergrass collected across the state of Florida from the napiergrass selected for biomass traits. These findings demonstrate that naturalized, weedy populations of napiergrass have a different genetic origin from the biomass types and validate the transferred DNA markers as an effective management tool for distinguishing between the two.