Brian A. Mealor

Crotalaria juncea (sunn hemp) is a tropical forage legume used as a cover, forage, and fiber crop. Sunn hemp seed production occurs primarily in India because it requires short days to flower and set seed. Seeds available for production are typically non-specific genotypes instead of true breeding varieties. As sunn hemp is grown in more locations, understanding not only its performance in different growing conditions but also variations in genotype performance is critical for production management. We evaluated the growth and biomass accumulation of four genotypes (KMB1, KMB2, Thailand Original Sunn, and ‘Tropic Sunn’) of sunn hemp grown in northern semi-arid and humid-continental environments, Wyoming (Adams ‘22 and ‘23 (irrigated), Wyarno ‘23 (rainfed)) and Minnesota (Morris ‘22 and ‘23), USA. Thailand Original Sunn had the fastest growth rate (height over time) but the slowest canopy closure (NDVI over time), while KMB1 had the slowest growth rate but the fastest canopy closure. While growth rates varied among sunn hemp germplasm, there were no marked differences in biomass accumulation when harvested at 60 and 90 days after planting. Although the genotype did not have a significant effect on biomass accumulation, the environment affected not only growth but also biomass accumulation. At 60 DAP, the sunn hemp biomass averaged 1836, 489, 2459, 3334, and 731 kg ha⁻¹ in the Adams ‘22, Adams ‘23, Morris ‘22, Morris ‘23, and Wyarno ‘23 environments, respectively. At 90 DAP, the sunn hemp biomass averaged 6459, 4573, 7979, 7403, and 2220 kg ha⁻¹ in the Adams ‘22, Adams ‘23, Morris ‘22, Morris ‘23, and Wyarno ‘23 environments, respectively. The growth rate, canopy closure, and biomass accumulation differed when compared between the semi-arid environments and the humid-continental environment, with the humid-continental environment producing faster growth and higher biomass. These findings support the hypothesis that genotypes are likely to perform as predicted within growing regions, but there may be room to improve performance in different environments through selective breeding.

Weeds in seed production systems are a major concern as competition can reduce yield while contamination of seed can increase cleaning costs or potentially lead to complete loss of marketable product. Indaziflam is an herbicide that remains within the top few centimeters of the soil leading to impacts only on the plants with roots within that zone. Our objectives were to evaluate indaziflam for annual weed control in established perennial grasses and to evaluate its effects on seed production and germinability. Indaziflam plus glyphosate was applied to a pre-existing stand of perennial grass species and cultivars in early spring 2017. First year yields indicated some damage occurred to specific perennial grasses. Subsequent growing seasons, however, typically showed either no impact of herbicide application or an increase in inflorescence number and (or) weight and germination. Long-term implications indicate that indaziflam may be an excellent option for annual weed management in seed production systems. Additional research is needed across a broader array of plant materials and in additional soil types and precipitation regimes to better develop recommendations for use of indaziflam in seed production situations.

Choosing appropriate plant materials for restoration projects can affect establishment and persistence of desirable species. In situations where herbicides are used to manage invasive weeds, plant materials able to tolerate herbicides at early growth stages could increase probability of successful restoration of vegetation. However, little is documented regarding relative herbicide tolerance of native species commonly used in restoration and information regarding intraspecific variation for such characteristics is missing. We conducted a greenhouse study in 2010 and repeated in 2011 to investigate seedling response of 17 desirable species (27 germplasm), Russian thistle, and downy brome to aminocyclopyrachlor, a relatively new herbicide with potential applications in reclamation and restoration. We applied aminocyclopyrachlor at six rates between 10 and 320 g ha⁻¹ 30 days after planting. Grasses were in the three to five leaf stage and forbs and shrubs were less than five cm tall at the time of herbicide application. We used a log-logistic model to estimate dry weight reduction in response to aminocyclopyrachlor rate. Russian thistle biomass was reduced 95% at 120 g ha⁻¹. At that same aminocyclopyrachlor rate, grass biomass was reduced 0 to 48% and flax and sagebrush species were reduced ≥ 77%. We document variation among and within species for relative tolerance to this herbicide. If aminocyclopyrachlor were used in a restoration project for postemergence control of Russian thistle, most grasses in this experiment would experience negligible biomass reduction whereas the selected sagebrush and flax species were highly susceptible at this early growth stage even at low aminocyclopyrachlor rates.

Ecological impacts of invasive plant species are well documented, but the genetic response of native species to invasive dominance has been often overlooked. Invasive plants can drastically alter site conditions where they reach dominance, potentially exerting novel selective pressures on persistent native plant populations. Do native plant populations in old exotic invasions show evidence of selection when compared to conspecific populations in adjacent, noninvaded areas? We employ amplified fragment length polymorphism (AFLP) analysis to screen a large number of loci from two native grass species (Hesperostipa comata (Trin. & Rupr.) Barkworth and Sporobolus airoides Torr.) that occur in old infestations of the invasive forb Acroptilon repens. We then compare observed locus by locus F_ST values with distributions of F_ST estimated from simulation models under expectation of neutrality. We also compare the proportion of loci possibly linked to selection and those not linked to selection which exhibit parallel trends in divergence between two community types (invaded, noninvaded). Few loci (H. comata, 2.6%; S. airoides, 8.7%) in the two native grasses may be linked to genes under the influence of selection. Also, loci linked to selection showed a greater portion of parallel trends in divergence than neutral loci. Genetic similarities between community types were less than genetic similarity within community types suggesting differentiation in response to community alteration. These results indicate that a small portion of scored AFLP loci may be linked to genes undergoing selection tied to community dominance by an invasive species. We propose that native plants in communities dominated by exotic invasives may be undergoing natural selection.