Toward plant breeding for multicrop systems

Abstract

Increasing cropping system diversity has great potential to address environmental problems associated with modern agriculture, such as erosion, soil carbon loss, nutrient runoff, water pollution, and loss of biodiversity. As with other agricultural sciences, plant breeding has primarily been conducted in the context of dominant monoculture cropping systems, with little focus on multicrop systems. Multicrop systems have increased temporal and/or spatial diversity and include a diverse set of crops and practices. In order to support a transition to multicrop systems, plant breeders must shift their breeding programs and objectives to better represent more diverse systems, including diverse rotations, alternate-season crops, ecosystem service crops, and intercropping systems. The degree to which breeding methods need to change will depend on the cropping system context in question. Plant breeding alone, however, cannot drive adoption of multicrop systems. Alongside shifts in breeding approaches, changes are needed within broader research, private sector, and policy contexts. These changes include policies and investments that support a transition to multicrop systems, increased collaboration across disciplines to support cropping system development, and leadership from both the public and private sectors to develop and promote adoption of new cultivars.

Keywords: crop diversity; cropping systems; plant breeding; sustainability.

Fig. 1.

Multicrop systems with varying degrees of spatial and temporal diversity. Each panel represents a different type of multicrop system, with shades of green representing different crop species. (A) Crop mixtures (e.g., grass-legume forage mixtures), (B) row intercropping (e.g., oat–pea row intercropping), (C) strip intercropping (e.g., corn–alfalfa strip intercropping), (D) field-scale crop diversification, (E) sequential planting of crop species within the same year (e.g., winter wheat–double crop soybean system), (F) relay intercropping (e.g., winter oilseed–soybean system), (G) long-term diversified crop rotation, and (H) perennial groundcover systems (e.g., an annual row crop rotation interplanted with perennial turfgrass or clover species).

Fig. 2.

The success of plant breeding for multicrop systems will require a set of enabling conditions, including appropriate policy, market demand, and other research supporting the development of multicrop systems. When setting up a breeding program for multicrop systems, core experimental activities should take place, including 1) defining a target population of environments, 2) identifying variation for performance in multicrop systems, 3) detecting interactions among mixture partners as well as environments and management systems, and 4) identifying traits of interest. These activities will inform the overall design and implementation of the breeding program. Implementation consists of successive cycles of selection, testing, and cultivar release. Breeding programs typically test many genotypes in fewer environments at the outset and expand the number of environments as best-performing genotypes are identified. The expected timeline for cultivar development and release varies by species, from 6 y to 8 y for an annual species to 25 y or more for perennial trees.