Abstract
Prospects for deploying perennial grasses that are currently considered leading candidates for dedicated energy crops over large acreages are debatable because of several limitations, including vegetative propagation or small seed size, low biomass production during the first growing season, and incomplete assessments of crop invasiveness risk. Pearl Millet-Napiergrass hybrids (“PMN”; Pennisetum glaucum [L.] R. Br. × P. purpureum Schumach.), in contrast, are large-seeded, sterile feedstocks capable of high biomass production during establishment year. Novel methods are warranted for confirmation of PMN hybrids, as traditional morphological observations can be inconclusive and chromosome number determination using cytological methods is laborious and time consuming. Six putative PMN lines were produced in this study, and 10 progeny from each line were evaluated using morphological traits, seed fertility, flow cytometry, and expressed sequence tag-simple sequence repeat (EST-SSR) markers. All putative hybrid lines were sterile and failed to produce seed. The PMN hybrids could not be distinguished from either parent using flow cytometry due to highly similar nuclear genome DNA contents. A number of paternal napiergrass-specific EST-SSRs were identified for each PMN line, and four paternal-specific EST-SSRs conserved across all napiergrass accessions were selected to screen the putative PMN hybrids. These EST-SSRs confirmed that all F1 individuals analyzed were PMN hybrids. The use of paternal-specific markers therefore provides a valuable tool in the development of both “Seeded-yet-Sterile” biofuel PMN feedstocks and additional PMN cultivar-and parental species-specific markers.
Highlights
Sustainable strategies are needed to develop biofuel systems that have high-energy efficiencies, low food security trade-off risks, and significant environmental conservation components
Six putative Pearl Millet-Napiergrass hybrids (PMN) lines were produced in this study, and 10 progeny from each line were evaluated using morphological traits, seed fertility, flow cytometry, and expressed sequence tag-simple sequence repeat (EST-SSR) markers
A number of paternal napiergrass-specific EST-SSRs were identified for each PMN line, and four paternal-specific EST-SSRs conserved across all napiergrass accessions were selected to screen the putative PMN hybrids
Summary
Sustainable strategies are needed to develop biofuel systems that have high-energy efficiencies, low food security trade-off risks, and significant environmental conservation components Because of their ability to efficiently utilize water and nutrients, perennial grasses such as Pearl Millet-Napiergrass hybrids × P. purpureum Schumach.) are promising sources of germplasm that can be grown for biomass production on more than 445 million hectares of marginal and abandoned agricultural lands worldwide [1,2,3] This can be done without affecting native prairie conservation programs because a vast majority of these marginal grasslands no longer contain native species and can provide a resource towards improved agricultural productivity via low-input, perennial grass cropping systems. Intercropping napiergrass with climbing legumes has been reported to increase soil nitrogen, soil carbon, and overall biomass yields [13,14], demonstrating the potential of legumes in providing renewable nutrient sources for PMN hybrids in reduced-input management systems
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