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Purpose Farmers need alternative approaches to manage nitrogen (N) that meet crop needs while reducing loss to the environment. Identifying crop genotypes that promote positive priming of organic matter in soil could help address this challenge. We aimed to 1) determine whether carrot genotypes differ in their potential to facilitate organic matter decomposition to scavenge N in soil, and 2) identify microbial taxa that are stimulated by carrot roots and thus could play a role in these processes. Methods We grew five genotypes expected to differ in N use efficiency in a nutrient-poor soil amended with 15N-enriched corn residue, tracked changes in carbon (C) and N pools, quantified microbial activity and bacterial community composition, and predicted the potential expression of microbial genes involved in soil C and N cycles. Results Experimental genotypes 8503 and 3999 had the greatest capacity to promote priming. Distinct bacterial communities from the families Micromonosporaceae, Chromatiaceae, and Rhodospirillaceae were enriched in the soils of genotypes most effective in scavenging N and this was correlated with genes responsible for β-glucosidase and nitrification activity. Conclusions Carrot genotypes do differ in the potential to stimulate microbially-mediated decomposition of organic materials indicating that it may be possible to begin selecting for this important trait.

Successful organic farming requires crop varieties that are resilient to environmental variability. Assessing variety performance across the range of conditions represented on working farms is vital to developing such varieties; however, data collected from on-farm, participatory trials can be difficult to both collect and interpret. To assess the utility of data arising from participatory trialing efforts, we examined the performance of butternut squash (Cucurbita moschataL.), broccoli (Brassica oleraceaL.) and carrot (Daucus carotaL.) varieties grown in diverse organic production environments in participatory trials in Oregon, Washington, Wisconsin and New York using adaptability analysis (regression of variety means on environmental index). Patterns of adaptation varied across varieties, with some demonstrating broad adaptation and others showing specific adaptation to low- or high-yielding environments. Selection of varieties with broadvsspecific adaptation should be guided by farmers’ risk tolerance and on-farm environmental variation. Adaptability analysis was appropriate for continuous variables (e.g., yield traits), but less so for ordinal variables and quality traits such as flavor and appearance, which can be vitally important in organic vegetable crop variety selection. The relative advantages of adaptability analysis and additive main effects and multiplicative interactions are also discussed in relation to on-farm trial networks. This work demonstrated the unique challenges presented by extensive participatory vegetable trialing efforts, which, as compared to grain crops, require novel approaches to facilitating farmer participation as well as data collection and analysis. Efficient, precise and reliable methods for evaluating quality related traits in these crops would allow researchers to assess stability and adaptation across a wider range of traits, providing advantages for effective plant breeding and trialing activities within the organic sector.

Participatory plant breeding (PPB), commonly applied in the Global South to address the needs of underserved farmers, refers to the active collaboration between researchers, farmers and other actors throughout the breeding process. In spite of significant public and private investments in crop variety improvement in the Global North, PPB is increasingly utilized as an approach to address cropping system needs. The current study conducted a state-of-the-art review, including a comprehensive inventory of projects and five case studies, to explore the emergence of PPB in the Global North and inform future PPB efforts. Case studies included maize (Zea mays), tomato (Solanum lycopersicum), Brassica crops (Brassica oleracea), wheat (Triticum aestivum) and potato (Solanum tuberosum). The review identified 47 projects across the United States, Canada and Europe including 22 crop species representing diverse crop biology. Improved adaptation to organic farming systems and addressing principles and values of organic agriculture emerged as consistent themes. While projects presented evidence that PPB has expanded crop diversity and farmer's access to improved varieties, obstacles to PPB also emerged including challenges in sustained funding as well as addressing regulatory barriers to the commercial distribution of PPB varieties. Agronomic improvements were only one lens motivating PPB, with many projects identifying goals of conservation of crop genetic diversity, farmers' seed sovereignty and avoidance of certain breeding techniques. The authors conclude that a multidisciplinary approach is needed to fully understand the social, political and agroecological influences driving the emergence of projects in the Global North and factors impacting success.

This chapter provides information on weed control, insect and nematode control, plant disease management, soil fertility, fertilizer application, seed production, and plant breeding in an organic carrot production.

With limited resources, plant breeders must make trade‐offs in resource allocation. While the randomized complete block design (RCBD) has been popular for agricultural research, it has been recognized that alternative experimental designs may better meet the goals of plant breeding. These alternative designs primarily address the issues with the RCBD that arise when blocks do not sufficiently control field variation. This occurs when the entry numbers are large (leading to large block sizes and heterogeneity within blocks), when field variation exists in more than one direction, or when there is insufficient seed or other resources available to replicate all entries. While these alternative designs have been widely adopted in large‐scale breeding programs of field or row crops (where they provide a clear and immediate benefit), they have been less widely used in small‐ to mid‐sized programs, where it is more difficult to evaluate the trade‐offs in accuracy and resource allocation between different field layouts of experimental designs. However, these programs also face the limitations of the RCBD and may benefit from the use of alternative designs. This chapter will review these designs as used in plant breeding, including incomplete block designs such as lattice designs and α‐designs, row–column designs such as Latin square and Latinized α‐designs, and partially replicated designs such as augmented designs and p‐rep designs. It will also cover variations of these designs, methods of design and analysis. We focus on considerations when using these designs in smaller trials, particularly when conducting organic, low‐input, or participatory plant breeding.

Managing pests in carrot production is challenging. Endophytic microbes have been demonstrated to improve the health and productivity of many crops, but factors affecting endophyte dynamics in carrot is still not well understood. The goal of this study was to determine how crop management system and carrot genotype interact to affect the composition and potential of endophytes to mitigate disease caused by Alternaria dauci, an important carrot pathogen. Twenty-eight unique isolates were collected from the taproots of nine diverse genotypes of carrot grown in a long-term trial comparing organic and conventional management. Antagonistic activity was quantified using an in vitro assay, and potential for individual isolates to mitigate disease was evaluated in greenhouse trials using two carrot cultivars. Results confirm that carrot taproots are colonized by an abundant and diverse assortment of bacteria and fungi representing at least distinct 13 genera. Soils in the organic system had greater total organic matter, microbial biomass and activity than the conventional system and endophyte composition in taproots grown in this system were more abundant and diverse, and had greater antagonistic activity. Carrot genotype also affected endophyte abundance as well as potential for individual isolates to affect seed germination, seedling growth and tolerance to A. dauci. The benefits of endophytes on carrot growth were greatest when plants were subject to A. dauci stress, highlighting the importance of environmental conditions in the functional role of endophytes. Results of this study provide evidence that endophytes can play an important role in improving carrot performance and mediating resistance to A. dauci, and it may someday be possible to select for these beneficial plant-microbial relationships in carrot breeding programs. Implementing soil-building practices commonly used in organic farming systems has potential to promote these beneficial relationships and improve the health and productivity of carrot crops.