Kevin Betts

Mechanism of Inheritance of Diclofop Resistance in Italian Ryegrass (Lolium multiflorum)l

A diclofop-methyl-resistant biotype of Italian ryegrass was characterized to determine the expression and inheritance of herbicide resistance and whether this trait was due to the presence of a diclofop-insensitive form of acetyl-coenzyme A carboxylase (ACCase). At the whole plant level, the resistant biotype was > 93-fold more resistant to diclofop-methyl than the susceptible biotype. Crosses of diclofop-resistant and -susceptible plants were performed to produce Fl plants. No maternal effects were evident in responses of reciprocal Fl plants to diclofop. GRSO diclofop rates determined for resistant, Fl, and susceptible plants were 15, 6.3, and 0.16 kg ha-1, respectively. F2 populations treated with a 7.5 kg ha-1 rate of diclofop exhibited three injury response pheno- types 3 wk after treatment: a susceptible (S) phenotype which was killed, an intermediate resistance (I) phenotype with severe injury, and a resistant (R) phenotype with little or no injury. Testcross progeny exhibited only I and S phenotypes. Observed segregation of phenotypes in F2 and testcross populations conformed to segregation ratios predicted for a trait with inheritance controlled by a single partially dominant nuclear gene. ACCase activity determined in crude cell-free extracts of resistant, Fl, and susceptible biotypes exhibited ISO values of 50, 20, and 0.7 FiM diclofop, respectively. A positive relationship between

Long-Term Biomass Yield and Species Composition in Native Perennial Bioenergy Cropping Systems

Biomass yield is an important factor when recommending native perennial plants and mixtures for bioenergy production. Our objective was to determine long-term biomass yields in fertilized and unfertilized native plant monocultures and mixtures that show promise for bioenergy across diverse environments in the Upper Midwest. We measured biomass yields, species composition, and diversity annually in monocultures and mixtures ranging from 4 to 24 planted species including grasses, legumes, and other forbs; each managed with and without 67 kg N ha–1 fertilizer applied annually at nine locations for 7 yr. Without N fertilization, switchgrass (Panicum virgatum L.) monocultures and an eight-species mixture of grasses and legumes produced the most biomass over locations and years (5.1 Mg ha–1). With N fertilizer, switchgrass monocultures and a four-species mixture of grasses produced the highest yields (6.8 and 6.4 Mg ha–1). Over time, biomass yields increased for switchgrass, decreased for Canada wild rye (Elymus canadensis L.), and remained stable for the high diversity mixtures. Other mixtures had nonlinear changes in yield, likely related to changes in species composition. Although the relative abundance of individual species changed over time, Shannon diversity was constant except for the four-species legume mixture where it decreased. Contrary to other studies, N fertilization did not decrease species diversity through time. Diversity was positively related to biomass yield following establishment, but the strength of the relationship diminished with stand age. Native plant mixtures managed with and without N fertilizer can yield similar biomass compared with highly productive monocultures in the Upper Midwest.

Plant roots and GHG mitigation in native perennial bioenergy cropping systems

Native perennial bioenergy crops can mitigate greenhouse gases (GHG) by displacing fossil fuels with renewable energy and sequestering atmospheric carbon (C) in soil and roots. The relative contribution of root C to net GHG mitigation potential has not been compared in perennial bioenergy crops ranging in species diversity and N fertility. We measured root biomass, C, nitrogen (N), and soil organic carbon (SOC) in the upper 90 cm of soil for five native perennial bioenergy crops managed with and without N fertilizer. Bioenergy crops ranged in species composition and were annually harvested for 6 (one location) and 7 years (three locations) following the seeding year. Total root biomass was 84% greater in switchgrass (Panicum virgatum L.) and a four‐species grass polyculture compared to high‐diversity polycultures; the difference was driven by more biomass at shallow soil depth (0–30 cm). Total root C (0–90 cm) ranged from 3.7 Mg C ha−1 for a 12‐species mixture to 7.6 Mg C ha−1 for switchgrass. On average, standing root C accounted for 41% of net GHG mitigation potential. After accounting for farm and ethanol production emissions, net GHG mitigation potential from fossil fuel offsets and root C was greatest for switchgrass (−8.4 Mg CO2e ha−1 yr−1) and lowest for high‐diversity mixtures (−4.5 Mg CO2e ha−1 yr−1). Nitrogen fertilizer did not affect net GHG mitigation potential or the contribution of roots to GHG mitigation for any bioenergy crop. SOC did not change and therefore did not contribute to GHG mitigation potential. However, associations among SOC, root biomass, and root C : N ratio suggest greater long‐term C storage in diverse polycultures vs. switchgrass. Carbon pools in roots have a greater effect on net GHG mitigation than SOC in the short‐term, yet variation in root characteristics may alter patterns in long‐term C storage among bioenergy crops.

Neo-Domestication of an Interspecific Tetraploid Helianthus annuus × Helianthus tuberous Population That Segregates for Perennial Habit

Perennial agriculture has been proposed as an option to improve the sustainability of cropping systems, by increasing the efficiency of resource use, while also providing ecosystem services. Neo-domestication, the contemporary domestication of plants that have not previously been used in agriculture, can be used to generate new crops for these systems. Here we explore the potential of a tetraploid (2n = 4x = 68) interspecific hybrid sunflower as a perennial oilseed for use in multifunctional agricultural systems. A population of this novel tetraploid was obtained from crosses between the annual diploid oilseed crop Helianthus annuus (2n = 2x = 34) and the perennial hexaploid tuber crop Helianthus tuberosus (2n = 6x = 102). We selected for classic domestication syndrome traits for three generations. Substantial phenotypic gains were made, in some cases approaching 320%. We also analyzed the genetic basis of tuber production (i.e., perenniality), with the goal of obtaining molecular markers that could be used to facilitate future breeding in this system. Results from quantitative trait locus (QTL) mapping suggest that tuber production has an oligogenic genetic basis. Overall, this study indicates that substantial gains towards domestication goals can be achieved over contemporary time scales.