Synchronizing cover crop flowering time with human demands in reduced-till organic agroecosystems: A comparative genomics approach

Background/Question/Methods

Agroecosystems can be major sources of nutrient loading into adjacent natural landscapes.  Organic farming seeks to reduce environmental impact, enhance ecosystem services and maintain profitability for farmers by relying crop rotation, cover cropping and minimizing off-farm inputs. Often Organic management results in reducing nutrient loads into adjacent natural landscapes. In conventional agricultural systems that utilize cover crops, pesticides are used in the spring to terminate growing cover crops in preparation for summer crop planting.  Pesticides are forbidden in organic systems therefore farmers must use alternative methods to terminate cover crops such as mowing and or rolling and crimping the cover crop.  Both mechanical approaches are dependent on cover crop phenology, specifically the plant must have transitioned from vegetative to reproductive growth to ensure an efficient termination.  We have identified six cultivars of the legume hairy vetch (Vicia villosa) that naturally differ in flowering time by over one month.  To understand the underlying genetic control of flowering we have used a comparative genomic approach to identify differences in genomic structure that may predict differences in flowering time among these cultivars.

We grew six cultivars hairy vetch (Vicia villosa) in the field over three seasons in a RCBD and monitored physiological development, biomass accumulation, biomass chemistry.  Every two weeks from mid winter through senescence, apical and axial meristems were sampled from each cultivar and immediately placed in liquid nitrogen.  DNA and RNA were extracted from each sample and subsequently used for either cloning and sequencing of genomic copies of the genes responsible for control of flowering in plants (e.g. flc, tfl, ft, co, pim, elf), or RNA was used for quantitative assessment of transcript copy number (qPCR of same gene targets) throughout the transition from vegetative to reproductive growth.

Results/Conclusions

  The Vicia villosa genes flc, tfl, ft, co, pim, and elf shared 70-85% identity with the homologous genes in closely related legumes such as pea (Pisum sativum) and barrel medic (Medicago truncatula).  A significant number of  single nucleotide polymorphisms (SNP) were found within gene families among the Vicia villosa six cultivars.  We confirmed that the target gene ft is a major inducer of transition from vegetative to floral development based on quantitative transcriptional analysis.  These results will enable identification of genetic elements that control major differences in flowering time among Vicia villosa cultivars and facilitate better crop selection by farmers employing sustainable farming system practices.