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.

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This supplementary information provides additional details for the measurement 3 techniques of immersion freezing of illite NX particles with S1.1. suspension techniques and 4 S1.2. dry-dispersed particle measurement techniques (both in alphabetical order as in Table 5 1). The discussions of measurement uncertainties of temperature and n s for each measurement 6 technique are also provided. We note that the uncertainty in frozen fraction (α) used in 7 calculating n s may not be adequate, since the sensitivity of Δα (an increase or a decrease in 8 frozen fraction) is much higher at high temperatures which unexceptionally coincide with a 9 low fraction of frozen illite NX. The BINARY setup is an optical freezing apparatus that makes use of the change in An immersion-freezing method was used to obtain INP temperature spectra for NX- 46illite clay, both when in bulk suspension and for size-selected particles. 47For the bulk clay, a 0.5 wt% suspension was made in 10 mM sodium phosphate buffer 48(at pH 8.7 to match the pH of the sample and to prevent flocculation, and filtered through a on a series of 20-fold dilutions to 3.1 x 10 -6 wt% in the same buffer. 52Polydisperse NX-illite particles were generated for size selection using the simple diameter-pore filtered). Filters were dried on foil in a particle-free, laminar flow cabinet, as 67were filter holder components after excess water was removed with a gas duster. 68After particle collection, the filter was transferred to a sterile, 50 mL Falcon Experimental uncertainties: The uncertainties for T and n s are ± 0.7 ˚C and ± 30%, 157 respectively. The n s uncertainty includes errors of the frozen fractions of drops, the specific 158 particle surface area, the particle masses per drop, and the drop sizes. fractions of drops, the specific particle surface area, the particle masses per drop, and the drop 225Experimental uncertainties: The accuracy of the thermistor embedded in the lower 226 aluminum block designed for the -40 < T < 0 °C and digitized with precision ±0.01°C. 227Repeatability of the temperature where 50% of pure water pico drops froze via homogeneous 228 nucleation was -35.7 °C ± 0.1 °C (n = 5, average diameter of drops ~86 µm). In comparison,