Case study of maize (corn)

The morphology and reproductive biology of maize make the breeding of maize relatively easy compared to other crops, but also create some limitations. The monoecious plants are large and produce large naked kernels that adhere to the ear (pistillate inflorescence). The staminate and pistillate inflorescences are physically separated on the plant making controlled pollination easy. The main downside is that pollen is dispersed by wind and while relatively heavy, can travel a considerable distance, making isolation somewhat difficult. Maize also suffers from relatively severe inbreeding depression.

The first hybrid maize cultivars were developed and commercialized in the US in the 1920s. These varieties were largely tailored to the Upper Midwest region of the US. The early benefits of hybrid maize to farmers were uniformity and standability. Uniformity also provided more predictability in plant behaviour and yield. Uniformity has come with a price of reduced genetic diversity and access to germplasm.

Prior to the broad adoption of hybrid maize in the 1930s and 1940s, farmers planted open-pollinated maize. According to Martin and Leonard (Reference Martin and Leonard1967), there were over 1000 different maize cultivars grown throughout the US in the early 1900s. PPB provides an alternative that centres farmers as active participants in variety development and seed production, rather than passive seed purchasers at the mercy of hybrid-dominant seed company offerings. The two maize cases reviewed cited meeting the needs of maize growers underserved by the dominant hybrid model.

The current study identified only two established maize PPB projects in the Global North, one in the US and one in Portugal (Table 2). A third project has recently been initiated in France, but no results are reported yet (Rey pers. com, 2021). Farmers established breeding priorities in both projects indicating a common recognition of the importance of centring their input for successful projects. The US project was initiated and grown with an equal partnership between the farmer and researchers. In contrast, researchers initiated the Portuguese project and then sought out an equal partnership with and buy-in from the farmers.

Table 2. Farmer-breeders (FB) and researcher-breeders (RB) roles in PPB in maize

The Portuguese Sousa Valley Project (VASO), was launched in 1984 by Dr Silas Pêgo (Mendes-Moreira, Reference Mendes-Moreira2006). Underpinning the project is Pêgo's Integrant Philosophy, which he developed in contrast to the Productivist Philosophy that had driven maize monoculture on the US landscape (Pêgo and Pilar Antunes, Reference Pêgo and Pilar Antunes1997; Mendes-Moreira, Reference Mendes-Moreira2006). The Integrant Philosophy model centres on both the agricultural system and the farmer as the most important decision-makers in the breeding process (Mendes-Moreira, Reference Mendes-Moreira2006). Motivations for the Portuguese researchers and farmers were to establish the integrant approach in on-farm polyculture systems and to preserve genetic diversity in open-pollinated varieties that was eroded with the introduction of high yielding hybrid maize introduced to Portugal by US companies after the Second World War (Mendes-Moreira and Pêgo, Reference Mendes-Moreira, Pêgo, Maxted, Dulloo, Ford-Lloyd, Frese, Iriondo and Pinheiro de Carvalho2012). The Sousa Valley region was selected in part because it is a traditional maize production area where maize still played a significant role in the polyculture system. In addition, the region's farmers were still growing traditional maize varieties used to make broa, a culturally significant Portuguese maize bread.

The project includes two parallel breeding programmes developed by researchers and farmer-cooperators. The researcher's programme combines three recurrent selection methodologies: phenotypic mass, S₁ and S₂ lines (Mendes-Moreira, Reference Mendes-Moreira2006). The farmer's programme uses an improved common mass selection methodology with two-parent control instead of the more traditional one parent control (Mendes-Moreira, Reference Mendes-Moreira2006; Mendes-Moreira et al., Reference Mendes-Moreira, Satovic, Mendes-Moreira, Santos, Nina Santos, Pêgo and Vaz Patto2017). The project has produced six improved populations that serve smallholder farmers growing for high-quality markets in sustainable systems (Mendes-Moreira, Reference Mendes-Moreira2006). Researchers believe that populations coming out of the VASO project can also serve as germplasm sources for the hybrid seed industry (Mendes-Moreira, Reference Mendes-Moreira2006). In this way, the integrant and productivist models could complement one another and offer underserved farmers throughout the world economic opportunities in seed production. Additionally, this would also increase genetic resources instead of replacing them with varieties bred for high-input industrial systems.

Conventional maize production in the US operates in what Pêgo defines as the productivist model focused on maximizing yields (Pêgo and Pilar Antunes, Reference Pêgo and Pilar Antunes1997). As a response to being underserved by this model, organic farmers and public and independent plant breeders developed the ‘who gets kissed?’ project to develop an open-pollinated sweet maize variety bred under organic systems (Shelton and Tracy, Reference Shelton and Tracy2015).

The project was initiated by an organic vegetable grower in Minnesota and a scientist with a non-profit research institute, and later joined by a public sector university plant breeder. The farmer was known in the region for his sweet maize, but was frustrated because his favourite varieties were often dropped by seed companies as they merged or closed. The farmer defined the desired traits and the breeding began with two populations from the university programme. Researchers designed a recurrent selection breeding programme in which, during each summer season, 100 full-sib families from each population were grown in Minnesota. Remnant seed from each family was saved in cold storage in Wisconsin. Researchers and the farmer were involved in quality evaluations, which made this activity much more of a social process than most plant breeding activities. Based on the data, 15–20 families were selected in each population. Remnant seed saved from the selected full-sib families was sent to winter nurseries in Chile where they were intermated within populations and full-sib families were generated for the next round of selection so that a full cycle of selection could be accomplished in 1 year (Shelton and Tracy, Reference Shelton and Tracy2015). They completed five cycles of selection and in 2014 chose to advance one population as the new open-pollinated sweet maize variety under the name ‘who gets kissed?’.

Given the interests of many in the US organic vegetable farming community ‘who gets kissed?’ was released with no intellectual property restrictions. Several regional breeding projects have grown out of ‘who gets kissed?’. Breeders and farmers in California, New Mexico, Oregon in the US, and in Australia are adapting it to their environmental conditions and local preferences (Colley et al., Reference Colley, McCluskey, Lammerts van Bueren and Tracy2021).

Case study of tomato

Tomato (S. lycopersicum) has many different market classes as well as types within market classes making breeding more complex. The major market class split is between processing and fresh market tomatoes. The former tends to be grown on a large, highly industrialized scale to produce tomatoes for canning, soups, sauces and juices. Fresh market tomatoes are diverse with cultivars varying for many traits including plant growth habits, fruit size, shape and colours. The predominant type in terms of the area produced are large-fruited red slicer types. These are often grown in southern temperate and subtropical regions for the winter fresh tomato market. Cherry tomatoes are the second most important market class. These have small red, yellow, orange or green fruit with round, oval or pear shapes. Most major seed companies have tomato breeding programmes, but these are focused primarily on the larger conventional agricultural markets (California and Florida in the US; Spain and Italy in Europe), or on types that are not necessarily in demand by fresh market organic growers (processing, wholesale glasshouse).

Outside of these generalizations, many tomatoes that vary from common market types are grown and sold regionally. Generally classed as ‘heirlooms’ in the US or ‘conservation varieties’ in Europe, more accurate terms we will use for the remainder of the paper are ‘heritage’ or ‘landrace’ tomatoes. As documented in the European case studies described below, some of the types of tomatoes that have been the subject of PPB have specific characteristics that are valued on a regional basis by growers and consumers. The number of heritage or landrace tomatoes is truly astounding. Nearly all of these were developed without a formal breeding approach and the tradition continues today.

Tomatoes are self-pollinated and lend themselves to varietal development as pure lines or may be utilized as inbreds in crosses to create F₁ hybrids. Most contemporary commercial tomato cultivars are F₁ hybrids and hybrid seed is produced by hand; the high ratio of seed obtained per cross makes F₁ hybrids economically feasible.

Organic fresh market growers consistently rank tomatoes as first or second in terms of vegetable crops needing genetic improvement to meet their production and marketing needs in all regions of the US (Lyon et al., Reference Lyon, Silva, Zystro and Bell2015; Brouwer and Colley, Reference Brouwer and Colley2016; Hultengren et al., Reference Hultengren, Glos and Mazourek2016; Dawson et al., Reference Dawson, Healy and McCluskey2017; Healy et al., Reference Healy, Emerson and Dawson2017). Some organic growers may find that commercial F₁ hybrids are not adapted to their production or marketing needs or may wish to save their own seed from year to year, which cannot be done with F₁ hybrids. Some growers and researchers conducting tomato PPB have justified their projects because of the need to breed varieties for regional adaptation as well as having the capacity to save seed.

Farmer participatory tomato improvement projects have focused on both fresh market and processing types with the main emphasis being field grown medium- to large-fruited types. Most are red fruited although yellow-fruited types have also been the subject of PPB. In the US, the most important types for organic fresh market growers have been indeterminate large-fruited red slicers, while in Europe, there has been an emphasis on the revival of traditional landraces, which vary in size and usage.

The current study identified seven projects in PPB of tomatoes (Horneburg, Reference Horneburg, Goldringer, Dawson, Rey and Vettoretti2010; Campanelli et al., Reference Campanelli, Acciarri, Campion, Delvecchio, Leteo, Fusari, Angelini and Ceccarelli2015, Reference Campanelli, Sestili, Acciarri, Montemurro, Palma, Leteo and Beretta2019; Lange et al., Reference Lange, Raj, Horneburg, Rahmann, Andres, Yadav, Ardakani, Babalad, Devakumar, Goel, Olowe, Ravisankar, Saini and Soto2018; Casals et al., Reference Casals, Rull, Segarra, Schober and Simó2019; Healy and Dawson, Reference Healy and Dawson2019; Rodriguez et al., Reference Rodriguez, Koutis, Annicchiarico, Nuijten and Messmer2020; Petitti et al., Reference Petitti, De Santis, Bocci, Lo Fiego, Di Luzio, Cerbino and Ceccarelli2021), four of which met our criteria for case studies (Table 3). Six of the seven projects were in Europe (Italy, Spain and Germany) and one in the US. The projects that were excluded were either too new to have achieved 3 years of activity, or they were primarily PVS rather than PPB projects. The pattern of activity compared to other crops is striking in that application of PPB to tomatoes is relatively recent and is concentrated in Europe. None of these projects can be said to have matured; while farmers are locally using selections from these projects, there do not appear to have been any formal variety releases. Traits under selection included yield and other horticultural traits in the field, but there was an especially strong emphasis on fruit quality traits including ˚Brix, dry matter, and flavour.

Table 3. Farmer-breeders (FB), researcher-breeders (RB) and commercial-breeders (CB) roles in PPB in tomato

^a Participatory variety selection.

Some of the European activity has focused on the revitalization of local landraces, and in some cases using these to breed improved forms of these landraces. For example, the Spanish project by Casals et al. (Reference Casals, Rull, Segarra, Schober and Simó2019) began as an effort to revitalize the ‘Mando’ local landrace, whose production had dwindled to a single grower. During grow-out and increase, variation from spontaneous outcrossing was observed, and breeders and farmers continued selections over years to stabilize some different yellow flesh lines that farmers thought had potential for commercialization. However, these were rejected on the basis of poor flavour by consumers in the final year of testing. On the other hand, production of ‘Mando’ did increase and the project was successful in preserving the landrace.

Campanelli et al. (Reference Campanelli, Acciarri, Campion, Delvecchio, Leteo, Fusari, Angelini and Ceccarelli2015) described a PPB project carried out in Italy to examine the significance of local adaptation in breeding for organic systems. Researchers first created four populations by selfing F₁s of four diverse crosses (a Cuor di Bue (Oxheart) fruit type, a long fruit type, a cherry fruit and a green salad fruit type). Seventy-two F₂s of each of the four populations along with check cultivars were planted in an unreplicated row−column design on four farms and a research station distributed across Italy. Both farmers and researchers evaluated populations and 201 selections over all locations were obtained. For the F_2:3 in on-farm trials, three selections by farmers, three by researchers, three by both and three by researchers only on-station for each of the four populations were planted. On the research station, six selections per population previously made by researchers were planted back at that site. From these, 115 plants were selected on-farm by farmers and researchers. Extensive replicated trials of selections in year three identified three out of 15 F_2:4 families that out-yielded commercial check cultivars, and these were being further developed for release. This study compared researchers' selections as opposed to those selections of farmers alone, and farmers' and researchers' joint selections, and found that the best performing were farmers' selections grown in the location in which they were selected. There was a clear pattern of specific adaptation to locality and production system.

Another project in Italy examined the effect of human (farmer) selection v. natural selection on specific adaptation (Petitti et al., Reference Petitti, De Santis, Bocci, Lo Fiego, Di Luzio, Cerbino and Ceccarelli2021). Starting with the same base population, farmers at different locations selected desirable plants and fruit from these was saved, while simultaneously, a population of 400 plants was advanced by single seed descent to the next generation. This process was carried out for two cycles followed by a third evaluation generation where all populations were grown at all locations for evaluation and further selection. Results from the comparative trial had not been published at the time of writing, but Petitti et al. (Reference Petitti, De Santis, Bocci, Lo Fiego, Di Luzio, Cerbino and Ceccarelli2021) found that the success of the project varied by region. There was strong interest by farmers and circulation of seed from selections in the southern region but in another region, researchers found that farmers did not use the types of tomatoes used to generate the breeding population, and that farm had to be replaced by another in the region after the second year.

The project reported by Campanelli et al. (Reference Campanelli, Sestili, Acciarri, Montemurro, Palma, Leteo and Beretta2019) illustrates an interesting approach to combining PPB with genomic analysis. The researchers conducted PPB using a tomato MAGIC (multiparent advanced generation intercross) population originally developed by the commercial company, ISI Sementi. The eight founder lines included seven contemporary tomato lines (representing a combination of paste and slicer types) and one wild species (S. cheesmaniae) selected for its productivity and biotic and abiotic stress resistance. Public researchers' breeding efforts began with a grow-out of 400 plants from the final eight-way cross, from which 30 plants were selected. Farmer selections began in the next generation where seeds of 370 MAGIC population plants plus 30 selections from the researchers' efforts were grown along with 25 standard cultivars on three farms in Italy representing north, central and south geographic regions. Researchers and farmers jointly selected plants based on a set of visual traits, then the fruit was brought back to the lab for testing ˚Brix, total solids and taste. Differences in mean values for plants selected in different regions were observed; those selected in the north had the greatest vigour and productivity, whereas those selected in the south had the highest brix and total solids. The objectives of this research spanned both researcher and farmer interests including developing a genetic resource for breeders and germplasm representing different market classes and traits of interest to farmers. Future research with these materials included growing all selections along with the eight parents and 500 highly inbred plants of the original MAGIC population, genotyping these and discovering SNPs associated with important field traits while examining the shift in allele frequencies as a function of selection in different regions.

In general, researchers considered tomato as a convenient crop for PPB, noting that the crop is well characterized genetically, that the reproductive biology and breeding methods for self-pollinated crops are translatable to on-farm research, traits of interest are easy to discern, there is a plethora of germplasm in the form of local landraces, there is strong interest in tomato improvement in the organic community and farmers willing to participate in PPB, and consumers have an interest in novel tomato types. A disadvantage is the large plant size which limits the number of plants that can be grown in farmers' fields. Researchers indicated that small to medium farm operations were often motivated to develop their own varieties and could accommodate around 100–300 plants with minimal compensation. However, larger operations tended to have a more rigid structure and tighter margins and were less inclined to engage in PPB. One characteristic of the tomato PPB projects is that they tended to be more regionally focused, perhaps because the needs of organic farmers across Europe are many and varied, thus local projects are more important than one that encompasses Europe. In some cases, it was apparent that researchers were not targeting the needs of farmers with their choice of initial material. In every case, the parents for crosses to develop populations were selected by researchers without overt input from farmers. Researchers may have had some idea of farmers' needs for markets, but farmers were not brought in from the beginning to design the project. Bringing in farmers at an earlier stage would probably allow better targeting of the project. All of these projects are relatively young considering the decade long duration of most breeding projects and have not had time to develop and formally release varieties. However, farmers are informally saving seed and producing the lines that work best on their farm, so while difficult to measure, the projects are generating impact.

Finally, an interesting dynamic was observed that may not play out with other crops, but probably affects the PPB landscape for tomatoes. Tomatoes are a very popular crop in the US with breeders at public institutions and with independent plant breeders. About a half-dozen universities in the US support tomato breeders who release fresh market and processed varieties. With independent plant breeders, Deppe (Reference Deppe2021) found that 11 of 35 breeders who release materials under an open seed source initiative (OSSI) agreement work on tomatoes. The Dwarf Tomato Project, an effort that began among growers on a tomato forum on Gardenweb, has released more than 100 varieties (Deppe, Reference Deppe2021). Seed Savers Exchange, a grassroots organization dedicated to preserving landrace varieties, lists 9911 entries of tomatoes on their Exchange website (SSE, 2021). It may be their popularity among independent breeders, and the ability of these breeders to satisfy growers and gardeners' needs that reduces the need for public/private PPB activities, especially in the United States. In Europe, the situation is somewhat different, with larger numbers of locally adapted landraces in need of adaptation to organic production. Also, the costs of the registration requirement for improved ‘conservation varieties’ for commercial sale in Europe can be a barrier to independent breeders (Petitti M., personal communication). Access to landraces may be more difficult because of the lack of a European-wide organization to preserve traditional varieties. PPB can play a vital role in preserving and improving traditional varieties and preventing their in-situ loss.

Case study of Brassica

Vegetable crops of Brassica (B. oleracea) are widely grown for premium organic markets across the US, CA and Europe including cabbage, cauliflower, broccoli and kale. Diverse landrace and heirloom varieties, originally domesticated in Europe, are still accessible for breeding (Chable et al., Reference Chable, Conseil, Serpolay and Le Lagadec2008). Until the 1980s open-pollinated varieties were grown commercially, but since then the seed trade-focused almost exclusively on the development of F₁ hybrids (F₁s). The shift towards F₁s was largely due to the allogamous nature of B. oleracea, the development of CMS and the use of double haploids to facilitate the production of inbred lines. F₁ breeding is primarily focused on achieving crop uniformity and narrowing the maturity window for mechanical harvests, further incentivizing breeders towards F₁ development for large scale, mechanized agriculture (Chable et al., Reference Chable, Conseil, Serpolay and Le Lagadec2008, Myers et al., Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012; McKenzie, Reference McKenzie2013). Yet, many organic producers seek quality traits with less emphasis on uniformity in the timing of maturity (McKenzie, Reference McKenzie2013). CMS use in breeding is also not in alignment with organic principles as in B. oleracea it is commonly derived through protoplast fusion, though there are also now organic breeding companies producing F₁s through naturally derived self-incompatibility. The use of double haploids is also questioned by the organic sector (Chable et al., Reference Chable, Conseil, Serpolay and Le Lagadec2008; Myers et al., Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012; Sahamishirazi et al., Reference Sahamishirazi, Moehring, Zikeli, Fleck, Claupein and Graeff-Hoenninger2018). All cases cited the avoidance of F₁ breeding techniques, lack of quality open-pollinated varieties, need for local adaptation and farmers' desire for greater control over their seed as reasons motivating participatory breeding (Chable et al., Reference Chable, Conseil, Serpolay and Le Lagadec2008; Myers et al., Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012; McKenzie, Reference McKenzie2013; McKenzie L., personal communication).

The current study identified five Brassica projects on PPB in the Global North, all located in the Pacific Northwest region of the US and the Brittany and Normandy regions of France where the locations share an environment optimum for seed production of a diversity of B. oleracea crop types (Table 4). Farmers established breeding priorities in all projects indicating a shared recognition of the importance of farmers' input from the start to ensure the outcome suits the target market and production environment. Researchers sourced germplasm and developed initial crosses in four of the five projects. In the case of kale in the US, the farmer initiated the project and only involved researchers in the advanced stage after frustrations of not achieving adequate uniformity for a variety release. The stage of researcher involvement varied in the early to advanced breeding phases with the researcher coordinating early phase population development in the case of broccoli and cabbage in the US, but the farmer leading early progress through mass selection in the US kale and purple sprouting broccoli projects and French cabbage and cauliflower projects. In all cases early to advanced breeding was conducted on-farm to leverage selection under the target environment. Researcher involvement in advanced breeding phases employed coordination of half or full-sib progeny selection methods with farmers' participating in the in-field evaluation and decisions in selection.

Table 4. Farmer-breeders (FB) and researcher-breeders (RB) roles in PPB in Brassica oleracea crops

Brassica crops are well suited to on-farm breeding as Myers et al. (Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012) noted, since advancements can easily be made through mass selection if enough genetic diversity is created and maintained as selection occurs prior to flowering. Selection in on-farm production fields can also serve as an advantage as the large population size allows leveraging selection pressure while maintaining adequate heterogeneity to avoid inbreeding depression (McKenzie L., personal communication). An added benefit is that farmers can harvest the crop for market, while evaluating quality and then subsequently harvest seed from select plants for breeding purposes (McKenzie, Reference McKenzie2013). On-farm reproduction of biennial crop types, including cabbage and some cauliflowers, can however be a barrier to PPB as they require conditions suitable for vernalization, either in the field or by lifting and storing plants through the winter which is likely why projects are limited to conducive production regions. The promiscuous nature of B. oleracea can also present a challenge to manage isolation on farms with diversified Brassica crops in production or nearby (McKenzie, Reference McKenzie2013). High levels of outcrossing, self-incompatibility and propensity for in-breeding depression present challenges in breeding Brassicas for recessive traits and achieving high levels of uniformity in open-pollinated populations (Myers J. R., personal communication; McKenzie L., personal communication). For this reason, researcher involvement in advanced breeding stages can aid in the implementation of progeny selection (Myers et al., Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012). The challenge of managing breeding populations given these biological factors may be one of the reasons; there are not many examples of Brassica PPB projects.

It is unlikely that open-pollinated Brassica varieties will achieve enough uniformity to replace the demand for F₁ varieties in large scale production, so it is likely that there will remain two different markets for hybrids and open-pollinated Brassicas unless there is increased pressure from organic regulations to restrict the use of CMS varieties or other market incentives. In spite of this fact, three of the four projects have already resulted in the release and commercialization of new open-pollinated varieties for specialized markets demonstrating the demand for alternatives to hybrid varieties.

Projects exhibited innovative breeding strategies that leverage farmers' and researchers' knowledge and resources while engaging multiple farmers as a participatory breeding network. The US broccoli breeding project followed a divergent−convergent scheme of population improvement, first described by Atlin et al. (Reference Atlin, Cooper and Bjornstad2001), in which a genetically diverse breeding population is distributed to farmers for on-farm selection and then recombined annually (Myers et al., Reference Myers, McKenzie, Voorrips, Lammerts van Bueren and Myers2012). This allowed decentralized selection under diverse farm environments leveraging farmers' input in selection criteria in the pre-breeding phase. After 7 years of population development, the researchers and two of the farmers each continued breeding through half-sib progeny selection for at least 6 years resulting in several new and distinct varieties. The cabbage and cauliflower projects in France similarly leveraged a farmer network, including seven farms, with breeding integrated into on-farm variety trials of heritage varieties from the French national seed bank. The researcher coordinated the farmers' variety evaluations. Each farm then conducted mass selection and saved seed from one variety ensuring a different variety was selected by each farm to preserve as much diversity as possible. Based on farmer's input the research institute then also crossed similar, but complimentary lines to generate new F₁ breeding populations for further on-farm selection and development of improved varieties. In the US cabbage project, the researcher facilitated the annual advancement of cabbage, a biennial, by lifting selected plants from the farmer's field and then reproducing in a greenhouse to advance the seed maturation early enough to again plant the following summer achieving annual selection. In the US kale project, the researcher self-pollinated plants by hand (bud pollination) to achieve full-sib progeny for repeated on-farm selection of families, a task too tedious to manage on a working farm. Each of these projects demonstrates the creative use of complementary skills and capacities to achieve greater advancement in B. oleracea development through farmer−researcher collaboration than could be achieved individually.

Case study of potato

Potato (S. tuberosum L.) is the fourth most important food crop worldwide, and also an important crop in organic farming systems. Consumers have different preferences as to tuber skin or flesh colour for consumption (including mealy to firm cooking types). But there are also special varieties for the processing industry such as french fries (long tuber shapes) or chips (round tuber forms).

Technically, making crosses in potatoes is not too complicated, but many factors influence the success (Tiemens-Hulscher et al., Reference Tiemens-Hulscher, Delleman, Eising and Lammerts van Bueren2013). Most varieties can be used as seed or pollen parents, but some varieties do not produce viable pollen. Some varieties only occasionally produce flowers and cannot be used for crossing. Sometimes flowers or berries are aborted, or pollen is not shed under conditions that are too moist or too dry. Most modern varieties are to a large degree self-pollinating, but in the field between 0 and 20% cross-pollination occurs by wind or bumble bees. Often the anthers are removed from the seed parent with a pair of tweezers to avoid self-pollination. Hand crossing can be done in the field early in the morning before bumble bees have visited the flowers. Parental tubers can also be planted in greenhouses in the ground or in buckets, enabling removal of the newly formed tubers to allow more inflorescences to be produced.

Potato is one of few vegetatively propagated root crops that are involved in participatory breeding programmes in the Global North: in the Netherlands (Lammerts van Bueren et al., Reference Lammerts van Bueren, Tiemens-Hulscher and Struik2008; Tiemens-Hulscher et al., Reference Tiemens-Hulscher, Lammerts van Bueren, Hutten, Lammerts van Bueren and Myers2012; Keijzer et al., Reference Keijzer, Lammerts van Bueren, Engelen and Hutten2021), Germany (Sieber et al., Reference Sieber, Forster, Diekmann, Sprengel, Kellermann, Dehmer and Hammann2018) and CA (Entz, Reference Entz2019), US (Genger, Reference Genger2018) (Table 5). The reasons for starting such programmes are the lack of available organically produced seed potatoes (CA and US). In Europe, such as in the Netherlands and Germany, potato breeding companies are interested in the organic market and provide sufficient quantities of organic seed potatoes, but their breeding programmes do not prioritize late blight resistance which is of high priority for most organic growers.

Table 5. Farmer-breeders (FB), researcher-breeders (RB) and commercial-breeders (CB) roles in participatory breeding projects on potato

^a First varieties are under registration trialling (2019).

^b Promising clones are handed over to commercial breeders for further selection (2018).

The potato programmes were usually initiated when researcher−breeders were approached by organic growers with an urgent call for action. As the late blight resistance genes that were derived from S. demissum are no longer effective, new resistance genes need to be introgressed from wild relatives and the expertise of specialized pre-breeders from one of the universities or institutes is required. Most cultivated potato (S. tuberosum L.) is tetraploid, so introgressing new resistance traits from wild relatives needs an extra step as many of them are diploid. Many wild relatives do not produce tubers and need to be converted from short day types to long day types to match the northern long day growing conditions. After the introgression and pre-breeding phase of some 10 to sometimes 20 years, including several generations of backcrossing the wild relative with modern varieties with good agronomic properties, the scientist breeders can then produce commercial crosses and distribute seeds from relevant crosses to the farmers to select during several early field generations. Some breeders provide true seeds and others grow out first-year seedling tubers for the growers. Usually, farmer-breeders select over 3–5 years and then return the selected, promising clones to the researchers or breeding companies who organize testing across various locations in replicated trials. The number of seeds or seedling tubers that farmers select on a yearly basis differs; in many programmes farmer-breeders yearly receive a minimum of 200 seeds up to 3000 of two or more populations. They discard approximately 95–98% in the first 3–4 years.

As the F₁ progeny of potato crosses are vegetatively propagated, the populations do not segregate. This makes it relatively easy for growers to be involved in the early stages of the programme, visually selecting clones that perform well, with good and regular tuber shape, smooth skin, good storability, sufficient disease resistance and other desirable traits.

As genotype-by-environment interaction is very large for potatoes, testing and selection over many years is needed to select a clone that is stable in performance across years and multiple locations. The programmes described above are not yet quite in the stage that clones can be marketed (usually up to 10 years of selection after the initial cross). However, some farmer-breeders sell quality clones through their own farm sales and do not pursue registration and commercialization (Table 5). Most projects aim at the commercialization of the selected clones. It is custom in the Netherlands to register a potato variety on the names of both the involved farmer-breeder and commercial breeder, so that ownership is shared which is expressed in sharing the royalties on a 50–50% base (Almekinders et al., Reference Almekinders, Mertens, van Loon and Lammerts van Bueren2014).

Specific to late blight being very sensitive to mutations under a high disease pressure, it is important to prevent the breakdown of late blight resistance by stacking various resistance genes (Pacilly et al., Reference Pacilly, Hofstede, Lammerts van Bueren and Groot2019). The advantage for farmer-breeders collaborating with universities is access to molecular markers for each source of late blight resistance which can be used to check whether the farmer's selected clones contain two or more resistance genes (Lammerts van Bueren et al., Reference Lammerts van Bueren, Østergård, de Vriend and Backes2010).

For many modern farmers, the skill of breeding has declined due to specialization. As a response, the Dutch project introduced a yearly training course for farmers or young breeders on potato breeding, and the course manual is published to make the practical potato breeding knowledge publicly available (Tiemens-Hulscher et al., Reference Tiemens-Hulscher, Delleman, Eising and Lammerts van Bueren2013).

Case study of wheat

Bread wheat (T. aestivum) has a large number of published projects ranging from conference proceedings to peer-reviewed journal articles. Projects exist in Europe (Dawson et al., Reference Dawson, Riviere, Galic, Pin, Serpolay, Mercier, Goldringer, Goldringer, Dawson, Rey and Vettoretti2010, Reference Dawson, Rivière, Berthellot, Mercier, de Kochko, Galic and Pin2011; Enjalbert et al., Reference Enjalbert, Dawson, Paillard, Rhoné, Rousselle, Thomas and Goldringer2011; Goldringer et al., Reference Goldringer, Enjalbert, Rivière and Dawson2012, Reference Goldringer, van Frank, Bouvier d'Yvoire, Forst, Galic, Garnault, Locqueville, Pin, Bailly, Baltassat, Berthellot, Caizergues, Dalmasso, de Kochko, Gascuel, Hyacinthe, Lacanette, Mercier, Montaz, Ronot and Rivière2019; Malandrin and Dvortsin, Reference Malandrin and Dvortsin2013; Rivière et al., Reference Rivière, Pin, Galic, de Oliveira, David, Dawson, Wanner, Heckmann, Obbellianne, Ronot, Parizot, Hyacinthe, Dalmasso, Baltassat, Bochède, Mailhe, Cazeirgue, Gascuel, Gasnier, Berthellot, Baboulène, Poilly, Lavoyer, Hernandez, Coulbeaut, Peloux, Mouton, Mercier, Ranke, Wittrish, de Kochko and Goldringer2013a, Reference Rivière, Goldringer, Berthellot, Galic, Pin, De Kochko and Dawson2013b, Reference Rivière, Dawson, Goldringer, David, Chable, Goldringer, Howlett, Barberi, Miko, Mendes-Moreira, Rakszegi, Ostergard, Brogen, Finckh, Pedersen and Bocci2014, Reference Rivière, Dawson, Goldringer and David2015; Rivière, Reference Rivière2014; Da Via, Reference Da Via and Trauger2015; Vindras-Fouillet et al., Reference Vindras-Fouillet, Rouellat, Hyacinthe and Chable2016; Petitti et al., Reference Petitti, Bocci, Bussi, Ceccarelli, McKeown, Spillane, Baćanović-Šišić, Dennenmoser and Finckh2018; van Frank, Reference van Frank2018; Berthet et al., Reference Berthet, Bosshardt, Malicet-Chebbah, van Frank, Weil, Segrestin, Rivière, Bernard, Baritaux and Goldringer2020; van Frank et al., Reference van Frank, Rivièr, Pin, Baltassat, Berthellot, Caizergues, Dalmasso, Gascuel, Hyacinthe, Mercier, Montaz, Ronot and Goldringer2020), CA (Bauta Family Initiative on Canadian Seed Security, 2013; Entz et al., Reference Entz, Kirk, Vaisman, Fox, Fetch, Hobson, Jensen and Rabinowicz2015, Reference Entz, Kirk, Jensen, Rabinowicz, Dey and Davis2016, Reference Entz, Kirk, Carkner, Vaisman and Fox2018; Kirk et al., Reference Kirk, Vaisman, Martens and Entz2015), and the US (Murphy et al., Reference Murphy, Lammer, Lyon, Carter and Jones2005, Reference Murphy, Carter, Jones and Kole2013; Lazor, Reference Lazor2008; Darby et al., Reference Darby, Monahan, Cummings, Harwood and Madden2013; Kissing Kucek et al., Reference Kissing Kucek, Darby, Mallory, Dawson, Davis, Dyck, Lazor, O'Donnell, Mudge, Kimball, Molloy, Benscher, Tanaka, Cummings and Sorrells2015; Kissing Kucek and Sorrells, Reference Kissing Kucek, Sorrells and Davis2016; Kissing Kucek, Reference Kissing Kucek2017) (Table 6). The large number of examples for bread wheat may be due to the existence of public plant breeding programmes at many universities and research institutions. It may also be due to the strong genotype by environment interactions that are observed in small grains, meaning that varieties developed for other regions or other management systems may not perform well for farmers in another region or using a different management system. The relative ease of logistics in managing participatory breeding projects with small grains is also likely a factor in the development of new projects.

Table 6. Farmer-breeders (FB), researcher-breeders (RB) and commercial-breeders (CB) roles in PPB in wheat

The motivation for starting participatory breeding projects often comes from farmers who have been unable to find suitable varieties for their production. In most examples here (Table 6), farmers have been targeting a value-added market for artisanal bread and have not found varieties that are competitive in organic production with the high quality they need for artisanal bread-making quality. Frequently crosses are made between higher-yielding modern varieties that have been tested in organic systems and landraces or historic varieties known for artisanal bread-making quality, particularly those known to produce high-quality bread at lower protein levels (i.e. around 10 v. 12.5% for most conventional bread wheat). High protein percentage in winter bread wheat is often achieved either by growing in areas with less rainfall and lower yield potential such as the Mediterranean or the Great Plains and intermountain region of the US. Participatory breeding programmes in areas with higher rainfall such as Northern France and the north-eastern and midwestern US have goals of increasing baking quality in winter wheat, which is preferred by growers because of its agronomic advantages but not by bakers due to its typically lower protein (Dawson et al., Reference Dawson, Rivière, Berthellot, Mercier, de Kochko, Galic and Pin2011; Kissing Kucek et al., Reference Kissing Kucek, Darby, Mallory, Dawson, Davis, Dyck, Lazor, O'Donnell, Mudge, Kimball, Molloy, Benscher, Tanaka, Cummings and Sorrells2015; Vindras-Fouillet et al., Reference Vindras-Fouillet, Rouellat, Hyacinthe and Chable2016; Kissing Kucek and Sorrells, Reference Kissing Kucek, Sorrells and Davis2016). In these climates, selection for resistance to Fusarium head blight (FHB, Fusarium graminearum) and resistance to pre-harvest sprouting is also critical, and these two traits are difficult to score on-farm. Participatory breeding projects in areas where bread wheat is typically grown often have goals of increasing yield under stressful conditions and lower inputs or organic systems while maintaining good artisanal bread-making quality.

The genotype by environment interactions seen in small grains often leads breeders and farmers to a decentralized model of selection to serve organic farmers in multiple ecological regions. There is also a lack of breeding in conventional systems for weed competitive ability or seed-borne disease resistance, which are major issues for organic farmers. Organic farmers frequently prefer lines that are taller with more tillering and biomass as long as lodging is minimal to compete with weeds during the season and to reduce the weed seed bank over the long term, as winter small grains are an excellent rotation crop to break up weed dynamics on organic farms that also grow row crops or vegetables. The desire for high biomass is also a trait that is more specific to organic farmers, who value the straw for soil building carbon or for livestock bedding or mulch. This is in contrast to goals of a high harvest index and a focus on grain yield in conventional systems.

In most cases, farmers approached the research team to initiate the project, often after trialling many modern and historic varieties which did not meet their needs. While there is a wide diversity of approaches to the details, there is a common breeding scheme that involves farmers proposing parental varieties to the research team, which makes the crosses in a greenhouse and then multiplies the first two generations on a research station or in a greenhouse without selection to get enough seed for farmers to plant in a small plot on their farm. In some cases such as France, the F₁ may be returned directly to the farmer who grows it in a protected plot (Dawson et al., Reference Dawson, Rivière, Berthellot, Mercier, de Kochko, Galic and Pin2011). In some other cases, the lines may be more advanced before they are put on farmers' fields, due to difficulties in finding small scale equipment for on-farm trials.

For most projects, on-farm trials start with the F₃ generation and are managed in small plots with shared equipment, either from the research team or from a farmers' organization. As bread wheat is a self-pollinating species with the harvested grain also being the seed for the next cycle of selection, on-farm management of multiple populations is primarily constrained by access to small plot scale equipment.

For the projects in this case study, the selection is done on-farm within populations by using negative selection to eliminate plants that are undesirable and positive selection to choose spikes from plants that have the desired characteristics. Farmers also choose between populations that come from different crosses. The selected spikes are frequently given to the research team for threshing and measurement (grain filling, protein content etc.) and then returned to the farmer for planting. Farmers frequently also visit research station trials of lines developed in the participatory breeding programme to observe and select among more lines than they can manage on-farm. Research station trials might include dozens of lines while on-farm trials typically have 5–10.

Projects vary in terms of how much selection is done on the research station to complement the on-farm selection. All projects have an on-farm selection and on-farm evaluations of more advanced lines involving more farmers. Some also add research station selection for certain traits. The project in France is based entirely on on-farm selection, with researchers measuring traits such as protein and thousand-kernel-weight on selected spikes to return information to farmers on the results of their selection (Dawson et al., Reference Dawson, Rivière, Berthellot, Mercier, de Kochko, Galic and Pin2011; Rivière, Reference Rivière2014). The project in the Northeast region of the US uses a combination of on-farm selection for production traits and on-station selection for traits like FHB and pre-harvest sprouting resistance, which are difficult to rate on-farm and is much more reliably scored in an inoculated nursery for FHB and in greenhouse misting conditions for pre-harvest sprouting, which are labour intensive and not realistic for an on-farm trial (Kissing Kucek, Reference Kissing Kucek2017). Similarly, pre-harvest sprouting is scored by researchers using a specialized nursery and greenhouse misting to create the ideal conditions for sprouting (Kissing Kucek, Reference Kissing Kucek2017). The research team also usually does grain protein and quality measurements are also done by the research team with information returned to farmers (Rivière, Reference Rivière2014; Kissing Kucek, Reference Kissing Kucek2017). Researchers may also do their own selection, often with input from farmers attending field days and winter meetings and maintain researcher and farmer selections in parallel.

Longer running projects have more varieties that are in production and in the stages just prior to release. For any participatory selection process, a long-term commitment is required to see results, both because of how long it takes to get from a cross to a new variety and because selection involves a learning curve for many farmers without prior experience, just as it does for new breeders. It can be difficult for farmers who are new to on-farm breeding to select efficiently. This can lead to unwanted increases in height of plants for example, or a reduction in tillering, or an unintentional reduction of diversity in the population. Managing on-farm trials can also be tricky and some experience is needed to manage the trial in a way that allows selection primarily on genetic merit rather than micro-environmental differences. As everyone learns, selection becomes more efficient and progress is clearer. Selection results after only a few years may not show many advantages to on-farm selection. However, after several years, projects in Manitoba, Washington, France, Italy and the north-eastern US all showed that farmer developed varieties had equivalent yields to modern varieties with some of the important additional traits that farmers developed and frequently greater stability over time and space than pure-line varieties. Varieties are in the release process in CA and the north-eastern US and are in production in France and Italy with each farmer doing their own seed multiplication due to more restrictive regulations on the types of varieties that can be commercialized.

The main difference in programmes in different geographic locations is in their ability to release lines from participatory projects as commercial varieties. Europe has the most restrictive seed regulations, and the varieties of the PPB programme cannot go through the normal commercialization process. The farmers seed network that developed these varieties however is not interested in commercialization or royalties from other farmers using their varieties. They see these varieties as a shared resource among members of the network, which each member can multiply and produce them on their own farms. About ten varieties have been named and circulated among the farmer group (Rivière P., personal communication). The Canadian system of registration is similar to the European one but is slightly more flexible and the fact that breeders participating in the projects have access to the registration trials and can put forward varieties developed with farmers means that these varieties may be commercialized and can also be grown by the farmers that developed them. In the north-eastern US, many farmers are not interested in producing their own seed due to the risk of seed-borne diseases, and the formal variety release process allows for the release of heterogeneous varieties as long as they can be adequately described. The varieties developed could either be released with a plant variety protection (PVP) certificate with farmers named as co-developers, or through an alternate mechanism such as the Open Source Seed Initiative (https://osseeds.org). There are regional independent seed companies interested in commercializing such varieties for the organic market.

In terms of methodology, many of these programmes are in close contact with one another to share best practices, and there are many similarities among the programmes. In Europe, farmers are more self-sufficient in terms of plot scale equipment and the ability to manage trials with farmers organizations. This is in part due to the fact that they have to produce their own seed of unregistered varieties so they have had to gain the knowledge and equipment to do so. In the US, typically individual farmers work directly with the research team, and other organizations help with coordination, communication and education, particularly in developing a market for the resulting varieties.

High-value markets for the varieties that result from PPB are critical, and one of the reasons that farmers become involved in these projects. The farms working on these varieties typically are interested in value-added production by creating a short chain from the farm to the consumer. This involves building on-farm mills and bakeries or working closely with local mills and artisanal bakers. In Europe, farms tend to be smaller in size, and more diversified with other crops (grains and vegetables/fruit/dairy/livestock for example) and rely more on very local marketing. In the US and CA, projects and markets are organized on a regional scale, with larger farms (although still smaller and more diversified when compared to conventional farms growing wheat). The common thread among all these projects is the desire to create well-adapted varieties for specific environmental conditions and management systems with excellent baking quality for local consumers.