Germination and Seedling Growth of Desmanthus illinoensis and Desmodium canadense in Response to Mechanical Scarification

Illinois bundleflower [Desmanthus illinoensis (Michx.) MacMill. ex B.L. Rob. & Fernald] and showy ticktrefoil [Desmodium canadense (L.) DC.] are legumes native to North America used during meadow restoration efforts. However, insufficient or slow germination or reduced emergence may result attributable to seedcoat-mediated reductions in permeability to water. The objective of this research was to determine the effectiveness of a single-speed electric scarifier lined with 40-grit sandpaper for increasing germination and seedling growth of two native legumes. Seeds of Illinois bundleflower and showy ticktrefoil were mechanically scarified for 3, 6, or 12 s before they were subjected to germination and vigor testing. After scarification, final germination percentage (FGP), germination rate, and uniformity at multiple temperatures (15, 20, and/or 20 to 30 °C) were improved for Illinois bundleflower. However, FGP decreased for showy ticktrefoil, whereas germination rate and uniformity increased. For both species, there was a decline in FGP with longer scarification durations. Illinois bundleflower seed subjected to scarification and accelerated aging (AA) had higher FGP than non-scarified seed subjected to AA (59% and 6%, respectively), whereas both scarified and non-scarified seed of showy ticktrefoil subjected to AA had low FGP (11% and 18%, respectively). Mechanical scarification increased electrical conductivity (EC) of leachates for both species, but scarified showy ticktrefoil seed subjected to AA resulted in the highest EC compared with all other treatments, indicating a reduction of vigor. Evaluation of a seedling grow-out test 3 weeks after sowing confirmed that emergence was enhanced after 3 s of mechanical scarification of Illinois bundleflower seed but that scarification of showy ticktrefoil seed decreased emergence and increased the number of abnormal seedlings. Mechanical scarification resulted in peripheral damage and seed tissue obliteration of both species as indicated by viewing with a stereomicroscope. We conclude that scarifier limitations caused excessive physical damage of showy ticktrefoil. For Illinois bundleflower, however, mechanical scarification using an electric scarifier increased emergence from 18% (non-scarified seed) to 77% after 3 s of scarification and FGP from 32% (non-scarified seed) to 87% after 3 s of scarification. Compared with responses from non-scarified Illinois bundleflower seeds, scarification treatment also resulted in 24% faster germination and 37% more uniformity.

Progress in breeding perennial grains

Annual cereal, legume and oilseed crops remain staples of the global food supply. Because most annual crops have less extensive, shorter-lived root systems than do perennial species, with a correspondingly lower capacity to manage nutrients and water, annual cropping systems tend to suffer higher levels of soil erosion and generate greater water contamination than do perennial systems. In an effort to reduce soil degradation and water contamination simultaneously – something that neither no-till nor organic cropping alone can accomplish – researchers in the United States, Australia and other countries have begun breeding perennial counterparts of annual grain and legume crops. Initial cycles of hybridization, propagation and selection in wheat, wheatgrasses, sorghum, sunflower and Illinois bundleflower have produced perennial progenies with phenotypes intermediate between wild and cultivated species, along with improved grain production. Further breeding cycles will be required to develop agronomically adapted perennial crops with high grain yields.

Effect of rotation crops on hatch, viability and development of Heterodera glycines

Rotation with non-host crops can be an effective method for reducing soybean cyst nematode (Heterodera glycines) populations in soybean cropping systems. Sunn hemp, Illinois bundleflower, oilseed rape, perennial ryegrass, red clover, corn and H. glycines-susceptible soybean were compared for their effects on H. glycines hatch, viability and development in laboratory and glasshouse experiments. In the laboratory experiments, root exudates in soil leachates, extracts from fresh plant tissues, and extracts from residues of sunn hemp, red clover and soybean stimulated hatch of second-stage juveniles (J2) of H. glycines. All crops appeared to contain hatch inhibitors as well. There was no apparent effect of the root exudates and extracts from any of the crops on egg viability in vitro. When the H. glycines J2 were exposed to root exudates and extracts for 72 h, only the extracts of fresh plants and plant residue from sunn hemp, red clover and soybean, and the extract of plant residue from oilseed rape reduced viability of J2. In glasshouse experiments, residues of all crops, except Illinois bundleflower, reduced egg population density, with sunn hemp providing the greatest reduction. Residues of sunn hemp, red clover, and perennial ryegrass added to soil reduced the reproduction factor, suggesting the residues not only reduced egg population density but also reduced nematode infectivity. While all crops allowed penetration by J2, minimal development (to third- or fourth-stage juveniles only) occurred only in sunn hemp, red clover, oilseed rape and Illinois bundleflower, and full development occurred only in soybean. The results suggest that sunn hemp and red clover were the most effective rotation crops for managing H. glycines, and that stimulating hatch of H. glycines J2 was the main mechanism involved in reducing the H. glycines population density.

Response to inoculation in Illinois bundleflower

llinois bundleflower [Desmanthus illinoensis (Michx.) MacMillan] has potential as a pasture and grain legume in the Midwestern USA, but has proven to be somewhat problematic in inoculation response. We identified inoculant-quality Rhizobium strains from among 120 isolates trapped from 12 sites within the native range of Illinois bundleflower, then determined the effect of inoculation with four selected strains on plant dry matter and plant total N in growth chamber, greenhouse, and field experiments. We also studied nodule occupancy in the field. In field experiments at Salina (Kansas) and Becker (Minnesota) inoculated plants yielded 170% greater dry matter and total N on average than did uninoculated and N fertilized controls at each site in the seeding year. There were no differences in plant response among the Rhizobium strains used, uninoculated plants were devoid of nodules, and the response to inoculation was similar for the three plant accessions considered. In the second growing season, plant regrowth was different at Salina and Becker. At Salina, all plant accessions regrew and no differences were found between inoculated and control treatments in the second year. At Becker, toward the northern extreme of the range for Illinois bundleflower, only a MN ecotype regenerated in the second year, and inoculation was a requirement for plant persistence. Regrowth was similar with each of the four inoculant strains used. While 90% of the rhizobia recovered from nodules in the seeding year at Becker had genetic fingerprints similar to the inoculant strains, in the second year this percentage had declined to 70%. Our results highlight the importance of Rhizobium strain selection if the use of native legumes is to be increased. Key words: Herbage, Illinois bundleflower, inoculant, native plants, nitrogen fixation, rhizobia

Rhizobium giardinii is the microsymbiont of Illinois bundleflower (Desmanthus illinoensis (Michx.) Macmillan) in midwestern prairies

Illinois bundleflower (Desmanthus illinoensis (Michx.) Macmillan) has potential as a grain and forage legume for the American Midwest. Inoculant-quality rhizobia for this legume have been identified but not previously characterized. Rhizobia trapped from 20 soils in the natural range of the Illinois bundleflower had characteristics that placed them overwhelmingly within the species Rhizobium giardinii, one of the few occasions this species has been recovered from legumes, raising questions on the biogeography and spread of midwestern prairie rhizobia.Key words: Rhizobium taxonomy, biogeography, diversity, prairie legumes.