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The explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a major component of munitions, is used extensively on military training ranges. As a result, widespread RDX pollution in groundwater and aquifers in the United States is now well documented. RDX is toxic, but its removal from training ranges is logistically challenging, lacking cost-effective and sustainable solutions. Previously, we have shown that thale cress ( Arabidopsis thaliana ) engineered to express two genes, xplA and xplB , encoding RDX-degrading enzymes from the soil bacterium Rhodococcus rhodochrous 11Y can break down this xenobiotic in laboratory studies. Here, we report the results of a 3-year field trial of XplA/XplB-expressing switchgrass ( Panicum virgatum ) conducted on three locations in a military site. Our data suggest that XplA/XplB switchgrass has in situ efficacy, with potential utility for detoxifying RDX on live-fire training ranges, munitions dumps and minefields. Switchgrass engineered to express two enzymes that degrade the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) detoxifies military sites contaminated with the munition when grown on these plots in a 3-year field trial.

Leymus cinereus (Scribn. & Merr.) Á. Löve and L. triticoides (Buckley) Pilg. are tall caespitose and short rhizomatous perennial Triticeae grasses, respectively. Circumference of rhizome spreading, proportion of bolting culms, anthesis date, and plant height were evaluated in two mapping families derived from two interspecific hybrids of L. cinereus Acc:636 and L. triticoides Acc:641 accessions, backcrossed to one L. triticoides tester. Two circumference, two bolting, and two height QTLs were homologous between families. Two circumference, seven bolting, all five anthesis date, and five height QTLs were family specific. Thus, substantial QTL variation was apparent within and between natural source populations of these species. Two of the four circumference QTLs were detected in homoeologous regions of linkage groups 3a and 3b in both families, indicating that one gene may control much of the dramatic difference in growth habit between these species. A major height QTL detected in both families may correspond with dwarfing mutations on barley 2H and wheat 2A. The L. cinereus parent contributed negative alleles for all four circumference QTLs, five of nine bolting QTLs, two of five anthesis date QTLs, and one of seven height QTLs. Coupling of synergistic QTL allele effects within parental species was consistent with the divergent growth habit and plant height of L. cinereus and L. triticoides. Conversely, antagonistic QTL alleles evidently caused transgressive segregation in reproductive bolting and flowering time.

PURPOSE: This study aimed to investigate comparatively the main chemical and physico-chemical properties of the humic acid (HA) fraction of three different composts and to evaluate the bioactive effects of these HAs on the germination and early growth of four populations of switchgrass. MATERIALS AND METHODS: Three compost HAs isolated from a green compost (HAGC), a mixed compost (HAMC), and a coffee compost (HACC) were characterized for some chemical and physico-chemical properties, such as ash content, elemental composition, total acidity, carboxylic and phenolic OH group contents, E₄/E₆ ratio, Fourier Transform infrared (FT IR), and fluorescence spectroscopies. In subsequent experiments conducted in vitro in a climatic chamber under controlled conditions, the bioactive effects of the three HAs at concentrations of 10, 50, and 200 mg L⁻¹ were tested on the germination and early growth of four switchgrass (Panicum virgatum L.) populations, the octaploids Shelter, Shawnee and Dacotah, and the tetraploid Alamo. RESULTS AND DISCUSSION: The ash content and the E₄/E₆ ratio were, respectively, much higher or slightly higher for HACC than for the other two HAs. HAMC showed the lowest C and H contents and the highest O content, whereas HAGC had the highest N content. The total acidity and phenolic OH group content followed the order: HAMC > HACC > HAGC. The fluorescence analysis of the three HAs evidenced a common fluorophore unit possibly associated to simple aromatic structures, such as phenolic-like, hydroxy-substituted benzoic and cinnamic acid derivatives. The FT IR spectra of all HA samples indicated the presence of aromatic phenolic structures. Significant beneficial effects were produced by any HA on switchgrass germination and early growth as a function of the population tested and the HA dose. CONCLUSIONS: Results of this study demonstrated that the addition of compost HAs to the germination medium of four switchgrass populations positively influenced the germination process and the growth of primary root and shoot. Significant correlations were found between HA bioactivity and some HA properties. These results suggest a possible use of compost as soil amendment in areas where switchgrass grows naturally or is cultivated.

Revegetation of disturbed semiarid lands requires rapid stabilization of ecological process and soil resources. Introduced species have been widely adopted because the slow establishment of native species frequently results in poor ecosystem recovery and further site degradation. Little research has documented the managerial possibilities and species interactions associated with simultaneously establishing native and introduced grasses on semiarid lands. We conducted a 3-yr experiment at Fort Carson, CO, to evaluate if seven native perennial grasses would coexist with either Russian wildrye Psathyrostachys juncea (Fisch.) Nevski, crested wheatgrass (Agropyron sp.), or Siberian wheatgrass A. fragile (Roth) Candargy after simultaneous seeding. Five grass mixes, each comprised of the seven natives and one introduced grass, and a standard military seed mix (mostly native grasses with a small introduced species component) were evaluated by comparing percentage ground cover of individual species. Predominance of crested and Siberian wheatgrass cover resulted in significantly lower native grass and weed abundance. In contrast, Russian wildrye and military treatments had lower introduced grass cover and high weed abundance, but much higher native grass cover. However, weed cover decreased to <5% in all treatments during the experiment. Western wheatgrass Pascopyrum smithii (Rydb.) A. Love was responsible for >80% of the native species cover in the military treatment for all 3 yr, whereas the Russian wildrye treatments had a more balanced mix of several native species. These results provide insights into managerial considerations for revegetation and weed control for frequently disturbed rangelands and suggest that some introduced grasses may coexist with native grasses.

The explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a major component of munitions, is used extensively on military training ranges. As a result, widespread RDX pollution in groundwater and aquifers in the United States is now well documented. RDX is toxic, but its removal from training ranges is logistically challenging, lacking cost-effective and sustainable solutions. Previously, we have shown that thale cress (Arabidopsis thaliana) engineered to express two genes, xplA and xplB, encoding RDX-degrading enzymes from the soil bacterium Rhodococcus rhodochrous 11Y can break down this xenobiotic in laboratory studies. Here, we report the results of a 3-year field trial of XplA/XplB-expressing switchgrass (Panicum virgatum) conducted on three locations in a military site. Our data suggest that XplA/XplB switchgrass has in situ efficacy, with potential utility for detoxifying RDX on live-fire training ranges, munitions dumps and minefields.

The explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), a major component of munitions, is used extensively on military training ranges. As a result, widespread RDX pollution in groundwater and aquifers in the United States is now well documented. RDX is toxic, but its removal from training ranges is logistically challenging, lacking cost-effective and sustainable solutions. Previously, we have shown that thale cress (Arabidopsis thaliana) engineered to express two genes, xplA and xplB, encoding RDX-degrading enzymes from the soil bacterium Rhodococcus rhodochrous 11Y can break down this xenobiotic in laboratory studies. Here, we report the results of a 3-year field trial of XplA/XplB-expressing switchgrass (Panicum virgatum) conducted on three locations in a military site. Our data suggest that XplA/XplB switchgrass has in situ efficacy, with potential utility for detoxifying RDX on live-fire training ranges, munitions dumps and minefields.

Depth and area of rooting are important to long‐term survival of plants on metal‐contaminated, steep‐slope soils. We evaluated shoot and root growth and metal uptake of four cool‐season grasses grown on a high‐Zn soil in a greenhouse. A mixture of biosolids, fly ash, and burnt lime was placed either directly over a Zn‐contaminated soil or over a clean, fine‐grained topsoil and then the Zn‐contaminated soil; the control was the clean topsoil. The grasses were ‘Reliant’ hard fescue (Festuca brevipila R. Tracey), ‘Oahe’ intermediate wheatgrass [Elytrigia intermedia (Host) Nevski subsp. intermedia], ‘Ruebens’ Canada bluegrass (Poa compressa L.), and ‘K‐31’ tall fescue (Festuca arundinacea Schreb.). Root growth in the clean soil and biosolids corresponded to the characteristic rooting ability of each species, while rooting into the Zn‐contaminated soil was related to the species' tolerance to Zn. While wheatgrass and tall fescue had the strongest root growth in the surface layers (0–5 cm) of clean soil or biosolids, wheatgrass roots were at least two times more dense than those of the other grasses in the second layer (5–27 cm) of Zn‐contaminated soil. When grown over Zn‐contaminated soil in the second layer, hard fescue (with 422 mg/kg Zn) was the only species not to have phytotoxic levels of Zn in shoots; tall fescue had the highest Zn uptake (1553 mg/kg). Thus, the best long‐term survivors in high‐Zn soils should be wheatgrass, due to its ability to root deeply into Zn‐contaminated soils, and hard fescue, with its ability to effectively exclude toxic Zn uptake.

Molecular genetic maps were constructed for two full-sib populations, TTC1 and TTC2, derived from two Leymus triticoides × Leymus cinereus hybrids and one common Leymus triticoides tester. Informative DNA markers were detected using 21 EcoRI–MseI and 17 PstI–MseI AFLP primer combinations, 36 anchored SSR or STS primer pairs, and 9 anchored RFLP probes. The 164-sib TTC1 map includes 1069 AFLP markers and 38 anchor loci in 14 linkage groups spanning 2001 cM. The 170-sib TTC2 map contains 1002 AFLP markers and 36 anchor loci in 14 linkage groups spanning 2066 cM. Some 488 homologous AFLP loci and 24 anchor markers detected in both populations showed similar map order. Thus, 1583 AFLP markers and 50 anchor loci were mapped into 14 linkage groups, which evidently correspond to the 14 chromosomes of allotetraploid Leymus (2n = 4x = 28). Synteny of two or more anchor markers from each of the seven homoeologous wheat and barley chromosomes was detected for 12 of the 14 Leymus linkage groups. Moreover, two distinct sets of genome-specific STS markers were identified in these allotetraploid Leymus species. These Leymus genetic maps and populations will provide a useful system to evaluate the inheritance of functionally important traits of two divergent perennial grass species.Key words: AFLP, perennial grasses, RFLP, STS, SSR.

Western wheatgrass (Pascopyrum smithii [Rydb.] A. Löve) has low seed production and poor germination and seedling vigor, limiting its use when quick establishment is needed to stabilize degraded rangelands. This study examined differences among germplasm sources and seed production environments on western wheatgrass seed traits. Seed was harvested from 10 western wheatgrass populations grown in three environments. Seed yield, seed weight, seedling germination, and seedling vigor were then determined. Seedling vigor was measured by greenhouse evaluation of seedling emergence percentage and rate from a planting depth of 6.35 cm. There were significant population x environment interactions for seed yield and seed weight. However, high Spearman's rank correlations between environments within each trait (r = 0.64 to 0.85, P = 0.048 to 0.002) suggested that environment had only a moderate effect on ranking of populations. Mean seed yield and 100-seed weight varied significantly among populations, ranging from 2.6 to 25.4 g plant⁻¹ and 0.43 to 0.54 g, respectively. Seed germination was high, ranging from 78.4 to 94.4%; however, population performance was not consistent across environments. Environment had no effect on seedling emergence rate, whereas emergence among populations ranged from 2.4 to 4.2 seedlings d⁻¹. Germination rate and seed weight were both correlated with seedling emergence rate (r = 0.57, P = 0.001 and r = 0.49, P = 0.01, respectively). These results indicated that seed production environment had little effect on western wheatgrass seed yield or seedling vigor and that it may be possible to breed for improvement in these traits by selecting among and within western wheatgrass populations.

Depth and area of rooting are important to long-term survival of plants on metal-contaminated, steep-slope soils. We evaluated shoot and root growth and metal uptake of four cool-season grasses grown on a high-Zn soil in a greenhouse. A mixture of biosolids, fly ash, and burnt lime was placed either directly over a Zn-contaminated soil or over a clean, fine-grained topsoil and then the Zn-contaminated soil; the control was the clean topsoil. The grasses were ‘Reliant’ hard fescue (Festuca brevipila R. Tracey), ‘Oahe’ intermediate wheatgrass [Elytrigia intermedia (Host) Nevski subsp. intermedia], ‘Ruebens’ Canada bluegrass (Poa compressa L.), and ‘K-31’ tall fescue (Festuca arundinacea Schreb.). Root growth in the clean soil and biosolids corresponded to the characteristic rooting ability of each species, while rooting into the Zn-contaminated soil was related to the species' tolerance to Zn. While wheatgrass and tall fescue had the strongest root growth in the surface layers (0–5 cm) of clean soil or biosolids, wheatgrass roots were at least two times more dense than those of the other grasses in the second layer (5–27 cm) of Zn-contaminated soil. When grown over Zn-contaminated soil in the second layer, hard fescue (with 422 mg/kg Zn) was the only species not to have phytotoxic levels of Zn in shoots; tall fescue had the highest Zn uptake (1553 mg/kg). Thus, the best long-term survivors in high-Zn soils should be wheatgrass, due to its ability to root deeply into Zn-contaminated soils, and hard fescue, with its ability to effectively exclude toxic Zn uptake.