Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/25/2012
Publication Date: 3/1/2012
Citation: Maul, J.E., Mothapo, N., Grossman, J., Mirsky, S.B., Emche, S.E., Devine, T.E. 2012. Linking a Germplasm Collection of the Cover Crop Hairy Vetch (Vicia villosa Roth) to Traits Related to Improved Nitrogen Fixation. Meeting Proceedings. 51: 2615-2625. Interpretive Summary: Hairy vetch is a nitrogen fixing cover crop used throughout the United States which can provide soil fertility, reduce weed pressure on crop plants and reduce soil erosion. Hairy vetch also provides important ecosystem services such as improved aggregate stability and increased soil carbon sequestration. Many traits found in hairy vetch have proven to be valuable to farmers practicing reduced input and organic farming methods and can contribute to overall farming system sustainability by reducing off farm inputs. Despite being a valuable crop component of sustainable agricultural systems, there has been little effort to improve hairy vetch trait characteristics. A review of the current literature reveled a lack of basic understanding of the genetic diversity found in cultivars of hairy vetch available to US farmers. We characterized the genetic relatedness of all 64 hairy vetch accessions available from the USDA Plant Germplasm collection using molecular biological approaches. We also linked differences in genetic diversity to traits important to farmers such as flowering date and cold hardiness. Additional experiments in collaboration with North Carolina State University showed that there are clear differences among hairy vetch cultivars in regards to nodulation and the community of symbiotic Rhizobial bacteria responsible for biological nitrogen fixation. Knowledge of the breadth of genetic diversity among hairy vetch cultivars form the basis for future breeding programs targeting improved traits such as; increased biomass production, improved nitrogen fixation capacity and synchronized flowering and development. This information will be used by breeders planning to target specific traits of interest as well as innovative farmers who engage in participatory or self-directed on-farm breeding programs.
Technical Abstract: Hairy vetch is used as a leguminous cover crop throughout the United States providing important ecosystem services in agro-ecosystems (Abdul-Baki et al., 2002; Mohler and Teasdale, 1993; Puget and Drinkwater, 2001; Seo et al., 2006; Stute and Posner, 1995). Many traits found in hairy vetch have proven to be valuable to farmers practicing reduced input and organic farming methods and can contribute to overall farming system sustainability by reducing off farm inputs. In spite of all the apparent benefits of a hairy vetch cover crop, there are constraints that have limited its wide scale adoption among vegetable and grain producers. One key constraint to farmer adoption is variability in biological nitrogen fixation among cultivars of hairy vetch available to growers. Hairy vetch (Vicia villosa Roth.) cultivation has multiple agronomic benefits, including biological nitrogen fixation (BNF) through mutual symbiosis with Rhizobium leguminosarum biovar viciae (Rlv). The use of legume cover crops can help reduce leaching and runoff losses by providing biologically-fixed N from slowly-decomposing cover crop residue, necessitating improved understanding of agricultural practices on legume-rhizobia interactions. We evaluated the effect of cultivation history on nodulation and BNF of ten hairy vetch cover crop genotypes using soil resident Rlv. Five groups of hairy vetch genotypes were inoculated with soil dilutions from six fields, three with hairy vetch cultivation history (HV+) and three without history (HV-). Nodule number, mass, and total plant nitrogen were assessed. Plants inoculated with HV+ soil dilutions averaged 60% greater nodule number and 70% greater nodule mass. Such plants also had greater plant biomass and total plant tissue N than those inoculated with soil dilutions from HV- fields, except in one site where no difference in N was found perhaps as a result of rhizobia population mixing between the HV+ and HV- fields. Host genotype also had a significant effect on nodulation, where some genotypes produced mean nodule numbers and mass that were 60% and 70% higher, respectively, when compared to the least nodulated genotypes. Plant biomass and plant tissue nitrogen were linearly correlated to nodule mass (r2 = 0.80 and 0.56 respectively). Variation in nodulation and BNF between host genotypes suggests that distinct genotypes may be used to breed cultivars with high symbiotic capacity with resident Rlv populations.