Organic Crop Breeding

Edith T. Lammerts van Bueren, James R. Myers, Edith T. Lammerts van Bueren, James R. Myers

• Editorial: Wiley-Blackwell
• Año: 2011
• ISBN:
  9781119949985
• Edición: 1
• Categoría: Technology & Engineering
• Categoría: Sustainable Agriculture

Organic Crop Breeding provides readers with a thorough review of the latest efforts by crop breeders and geneticists to develop improved varieties for organic production. The book opens with chapters looking at breeding efforts that focus on specific valuable traits such as quality, pest and disease resistance as well as the impacts improved breeding efforts can have on organic production. The second part of the book is a series of crop specific case studies that look at breeding efforts currently underway from around the world in crops ranging from carrots to corn. Organic Crop Breeding includes chapters from leading researchers in the field and is carefully edited by two pioneers in the field.

Organic Crop Breeding provides valuable insight for crop breeders, geneticist, crop science professionals, researchers, and advanced students in this quickly emerging field.

Section 1

General Topics Related to Organic Plant Breeding

1

Organic Crop Breeding: Integrating Organic Agricultural Approaches and Traditional and Modern Plant Breeding Methods

Edith T. Lammerts van Bueren and James R. Myers

Introduction

Organic agriculture is continuously growing worldwide on land and farms in more than 160 countries as well as in the global marketplace (Willer and Kilcher, 2011). Globally, there are 37.2 million hectares of organic agricultural land (including in-conversion or transition hectarage), which is about 0.9% of all arable lands. Of the total organic area in 2009, most (24.9%) is in Europe, followed by Latin America (23.0%), Asia (9.6%), North America (7.1%), and Africa (2.8%). Some individual countries (mainly those in Europe) had higher percentages due to support by national policies, e.g., Austria (18.5%), Sweden (12.6%), and Italy (9.0%; Willer and Kilcher, 2011).

Organic agriculture has its origins in the early 1900s with individuals advocating that “living soil” was a fundamental value of sound agriculture (Balfour, 1943; Howard, 1940; Pfeiffer, 1947; Steiner, 1958; Rodale, 1961). It was not until the 1970s that the organic movement grew substantially, however. Growth of the movement coincided with consumers’ and farmers’ reactions against the unsustainable environmental impact of the agriculture of that time. In the 1990s, organic agriculture became large enough to attract the interest of major food suppliers. In 2008--2009 organic products occupied about 5% of the market and were worth 55 billion US dollars, or 40 billion euros (Willer and Kilcher, 2011). To date, increasing development in the organic sector is influenced by three main drivers: Values (see four basic principles of the International Federation for Organic Agricultural Movements in Chapter 7), protest (promoting organic agriculture as an alternative strategy) and market (an economic interesting niche market). Alrøe and Noe, 2008.

Regulations translating the values and principles of the organic sector into rules and standards (IFOAM, 2005; Luttikholt, 2007) have been harmonized to promote global trade. The four basic principles of the organic movements as described by the world umbrella organization IFOAM, include (a) the principle of health: Expressing the concept of wholeness and integrity of living systems and supporting their immunity, resilience, and sustainability; (b) the principle of ecology: Promoting diversity in site-specific ecological production systems; (c) the principle of fairness: Serving equity, respect, justice, and stewardship of the shared world; and (d) the principle of care: Enhancing efficiency and productivity in a precautionary and responsible way (IFOAM, 2005; Luttikholt, 2007).

These principles have been codified in governmental regulations such as the National Organic Program (NOP) in the United States (USDA, 2002) and in Europe by the European Commission (EC, 2007).

It was only in the early 1990s that crop breeding and seed production came to the fore as an issue for organic growers and consumers in response to the emerging field of genetic engineering (GE) and strengthening of intellectual property rights. The organic sector began to discuss ways to actively stimulate crop improvement to meet organic principles.

In this chapter we will describe how organic management differs from conventional agricultural management, what plant traits are required for optimal adaptation to organic farming systems, and ways to acquire such adaptation via cultivar selection, seed production, and breeding. We also summarize the history and future perspectives for organic crop breeding in the United States and Europe.

How Different Are Organic Farming Systems?

When the U.S. National Organic Standards Board convened to advise the USDA on developing organic regulations, they described organic agriculture as:

“… an ecological production management system that promotes and enhances biodiversity, biological cycles, and soil biological activity. It is based on minimal use of off-farm inputs and on management practices that restore, maintain, and enhance ecological harmony” (USDA, 2002).

Organic farming is more than merely replacing chemical pesticides and fertilizers with organic ones. Emanating from the principles of health and ecology, the aim has been to move away from curative measures and to amplify agro-ecological system resilience by developing preventative strategies at the system level (e.g., Kristiansen et al., 2006; see table 1.1). The goal is to stimulate a high level of internal system self-regulation through functional diversity in and above the soil, as opposed to depending on external inputs for regulation (Østergård et al., 2009).

Table 1.1 Overview of the main difference in crop management between conventional agriculture, sustainable low-external input farming systems and organic farming systems

In considering differences among current farming systems in Western societies (e.g., conventional with high-external inputs systems, conventional systems reducing external inputs to become more sustainable, and organic farming systems) organic farming systems are the most extreme of the three types in refraining from chemical-synthetic inputs and in using preventative rather than curative measures. Although conventional low-external input farming seeking sustainability can be considered an intermediate between high-external input farming and organic farming, there is still a critical difference. It aims to reduce the input levels through precision farming methods and integrated pest management but still relies on chemical inputs to quickly correct during crop growth. In contrast, organic farming systems that cannot (easily) “escape” by applying curative methods rely on indirect, long-term strategies of fostering systems resilience. Organic farming systems focus on soil building through increasing organic matter, which increases water holding capacity and buffers against perturbations to the system. Such systems generally lack short-term controls (e.g., by applying mineral fertilizers with ready water-soluble nutrients or pesticides) to modify the growing environment during the season. Because organic farmers have fewer means to mitigate environmental variation, the varieties grown in organic agriculture will exhibit larger genotype by environment interactions, with greater emphasis placed on cultivar traits that allow adaptation to variable growing conditions (Lammerts van Bueren et al., 2007).

Another important difference among the aforementioned farming systems is that the main source of nitrogen (N) in organic farming systems is mineralization of organic matter, making N availability less controllable (Mäder et al., 2002). Under low temperatures in spring, soil microbiota that mineralize organic matter are not active enough to provide sufficient N, causing crop growth to lag and allowing weeds to compete. This requires cultivars that can cope with early season low fertility and produce vigorous growth to cover the soil as early as possible.

Consequences for Cultivar Requirements

A conclusion drawn from the description in the previous section is that conventional agriculture has more external means to adapt the environment to optimal crop growth, whereas organic farming systems need cultivars to adapt to the given environment. Crops bred for conventional production may be adapted to a narrower range of environmental conditions, especially those controlled by the external inputs of the grower. Therefore, cultivar selection is more critical for organic than for conventional farmers. The emphasis is on choosing flexible, robust cultivars that are adapted to such farming systems and that possess yield stability and can compensate for unfavorable conditions.

Organic growers have largely depended on cultivars bred for conventional systems, but not all are optimal for organic farming systems because traits associated with independence from external inputs have not received high priority in current breeding programs.

Traits

A focus on breeding for organic agriculture would require a shift from emphasis on maximizing the yield level in combination with the use of “crop protectants” to an emphasis on optimal yield stability. One of the main characteristics of organic farming is a multilevel approach to increasing system stability to reduce risk of failures. A similar approach could apply to cultivar development to adapt to less controllable and unfavorable growing conditions (see table 1.2). The aim would then not only be adaptation to low nutrient levels supported by improved interaction with beneficial soil mycorrhizae, but also morphological and phytochemical traits that reduce disease susceptibility (wax layers in Brassica species, open plant architecture), enhance weed competition (early vigor and planophile growth habit), and increase in flavonoids and glucosinolates (pest feeding deterrents; Stamp, 2003; Züst et al., 2011).

Table 1.2 Differences in plant ideotype between high input conventional and low-input organic cropping systems

Conventional	Organic
Above-ground traits
Performs well at high population density	Optimal performance at lower densities
Increased harvest index	Increased harvest index, but not as dramatic as for conventional production
Erect architecture and leaves, shortened plant stature	Taller plants, spreading canopy to be productive in low input situations
Weeds controlled by herbicides	Weeds limited by competition (plant height, spreading architecture), plants tolerate cultivation
Yield is maximized with high level of inputs	Maximized sustainable yield achievable with input of nutrients from organic sources
Pest and disease resistance to specific complex of organisms; need for resistance to diseases of monoculture systems	Pests and pathogens of monoculture potentially less severe, pathogen and pest complex differ; induced resistance relatively important; secondary plant compounds important for pathogen and pest defense
Rhizosphere traits
Root architecture unknown	Exploratory root architecture; able to penetrate to lower soil horizons
Adapted to nutrients in readily available form	Adapted to nutrients from mineralization – not readily available; need for nutrient use efficiency; responsive to mycorrhizae
Legume-specific traits
Nitrogen production by rhizobia of lesser importance	Rhizobia more important; discrimination against infective rhizobia important for N acquisition
Harvest and marketing traits
Improved labor efficiency	Incorporate traits that improve working conditions
Improved processing, packing, and shipping efficiency	Improved nutrition, taste, aroma, and texture
Crop shaped by mechanical harvest constraints	Traits priorities set jointly by researcher and farmer

From Cultivar Evaluation to Organic Seed Production and Plant Breeding Programs

Just as conventional colleagues do, organic farmers are always looking for the best cultivars to meet their needs. As described above, cultivar choice is a valuable tool of organic farmers to increase system and yield stability. Many research projects have emphasized farmer participatory trials to evaluate current cultivars to select the best performing cultivars under organic growing conditions. The next step in evolution to an organically based breeding program has been to produce organic seed of the most suitable conventionally bred cultivars. The subsequent step has been to identify “ecological” traits that should be included in current breeding programs. Often breeders interested in breeding for low-input or organic farming have also found that the protocols for cultivar testing need to be adapted to allow appropriate cultivars to enter the market (e.g., as in Europe; Löschenberger et al., 2008; Rey et al., 2008; see Chapter 8).

The final step in program evolution has been to develop...