The Role of Crop-Pollinator Relationships in Breeding for Pollinator-Friendly Legumes: from a Breeding Perspective
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Euphytica (2009) 170:35–52 DOI 10.1007/s10681-009-9953-0 The role of crop-pollinator relationships in breeding for pollinator-friendly legumes: from a breeding perspective Reid G. Palmer Æ Paola T. Perez Æ Evelyn Ortiz-Perez Æ Fouad Maalouf Æ Marı´a Jose´ Suso Received: 4 December 2008 / Accepted: 27 April 2009 / Published online: 21 May 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Breeders are encouraged to develop breed- to enhance pollinator conservation as well as crop yield ing approaches that strive to integrate food production and yield stability. We analyze how understanding into the healthy functioning of agro-ecosystems. In the crop-pollinator relationships (CPR) can contribute to case of legumes, this approach should preserve bee the production of high-yielding and pollinator-friendly fauna by providing suitable floral resources within the varieties by examining: (1) The status of knowledge on crops themselves. In parallel, legume breeding for mating systems and floral traits; (2) The contribution of sustainable agriculture is linked to the development of CPR understanding to plant breeding for both hybrid- environmental services. Foraging places and nesting seed production and open-pollinated population sites for solitary and social bees are some of the improvement. ecological services provided for legumes. Crops with floral attractiveness and rewards for insects can be used Keywords Bee pollinator Á Floral traits Á Heterosis Á Hybrid and population improvement Á Soybean Á Faba bean The authors R. G. Palmer and M. J. Suso contributed equally to this work. & R. G. Palmer ( ) Introduction USDA-ARS-CICGR, Iowa State University, Ames, IA 50011, USA e-mail: [email protected]; [email protected] Biologists recently compiled a world check list of bees. Nearly 19,500 bee species were identified on six R. G. Palmer Á P. T. Perez continents (Integrated Taxonomic Information Sys- Department of Agronomy, Iowa State University, Ames, IA 50011, USA tem (ITIS), http://www.itis.gov/beechecklist.html). Scientists have estimated that the worldwide eco- E. Ortiz-Perez nomic value of the pollination services provided by Dairyland Seed Co., Inc, Otterbein, IN 47970, USA insect pollinators in 2005 was about €153 billion F. Maalouf (Gallai et al. 2009). This figure amounted to 9.5% of Biodiversity and Integrated Gene Management, the total value of world agricultural food production. ICARDA, P.O. Box 5466, Aleppo, Syria Furthermore, the value per hectare of crops that depend on insect pollinators for their production was M. J. Suso Instituto de Agricultura Sostenible, CSIC, on average much higher than that of crops not pol- Apdo. 4084, Cordoba, Spain linated by insects. There was a positive correlation 123 36 Euphytica (2009) 170:35–52 between the value of a crop category per production number of social, eusocial, and solitary bees, which unit and its ratio of vulnerability based on its can be commercial, feral, or wild (Free 1993; dependence on insect pollinators. Delaplane and Mayer 2000). Foraging places and Climate changes exacerbate concerns about agri- nesting sites for solitary and social bees are some of cultural production and food security worldwide the ecological services provided by legumes in a (Rosenzweig and Parry 1994; Chmielewski et al. sustainable agriculture. The provision of floral 2004). At the global level, ecosystems are under resources within the crop for supporting beneficial threat; both productivity and geographic distribution insect pollinator populations could be a promising of crop species will be affected. This, in turn, will strategy to enhance environmental function of affect insect pollinators and plant pollination. For legumes. Consequently, we face a situation where example, air pollution can lead to reductions in the the development of pollinator-friendly cultivars is concentration of volatile compounds that insects needed. Such a situation may require a re-thinking of detect as they forage for nectar and pollen (McFred- crop breeding strategies and objectives. erick et al. 2008). Faba bean plants growing under The role of bee pollinators as agents of pollination elevated CO2 conditions showed an increased floral and of hybridisation needs to be considered. Pollin- display and may be more attractive to pollinators, but ators help increase seed set and self-pollination, but pollen flow may not necessarily be improved more importantly enhance cross-pollination (Richards (Osborne et al. 1997). 2001). Pollinators as agents of cross-pollination can Changes in crop management techniques, particu- contribute to breeding strategies. Crops with suitable larly the intensification of cropping, reduction/change floral attractiveness and rewards can be used to foster in crop rotations, and increases in monocultures, have pollinator conservation, which in turn may lead to intensified the activity of pests (Rosenzweig et al. improved seed set and/or improved crop yields as well 2002). The expansion of world trade in food and plant as increased resistance to biotic and abiotic stresses. products has increased the impact of weeds, insects, There are good breeding reasons as well as and diseases on crops. International movement of ecological reasons for improved targeting of crop- insect pollinators, and their associated pests, was pollinator relationships (CPR) (Westerkamp and offered as a possible contributor to colony collapse Gottsberger 2000; Aizen et al. 2008). Optimising disorder (CCD) of honeybee colonies in the US. CPR would be a key to the establishment of breeding Adaptive modifications initiated by agriculturists, strategies that increase yield and its stability by using horticulturists, and foresters can help to minimize the social and solitary bees, thereby facilitating the negative impacts of a decline in insect pollinators. An development of ‘‘pollinator-friendly’’ cultivars. The example is the recent trend in sustainable agriculture beauty of this breeding strategy is that farmers might for environmental priorities to be incorporated into get additional income from conservation payments, plant breeding objectives (Mena et al. 2005). Follow- and simultaneously from conserving biodiversity ing reports of declines in solitary and social bees, (Morandin and Winston 2006). And the farmer would breeders were encouraged to develop breeding still continue to get high yield and yield stability. approaches that strive to integrate food production The benefits of approaching legume improvement into the healthy functioning of agro-ecosystems by applying an understanding of CPR are both direct (Allen-Wardell et al. 1998; Maria-Klein et al. 2007). (seed yield and stability increase) and indirect (con- In the particular case of legumes, this approach could servation of biodiversity and beneficial insects). To help preserve and enhance bee fauna by providing make effective progress in breeding for pollinator- suitable floral resources within the crops themselves. friendly varieties, there are two complementary In parallel, legume breeding for sustainable agri- aspects of breeding that need consideration. Firstly, culture is linked to the development of non-food breeding efforts and technologies should carefully services such as environmental services (Helenius match plant and pollinator requirements; yield, yield and Stoddard 2007). Legume improvement demands stability, and resistance to stresses on one hand and a shift in emphasis in breeding programmes from pollinator needs on the other. Secondly, these varieties yield alone towards additional emphasis on environ- may require the introduction of new traits or the mental function. Legumes are visited by a great enhanced expression of existing traits to optimize CPR. 123 Euphytica (2009) 170:35–52 37 How can the understanding of CPR contribute to alternative methods to manipulate pollen dispersal underpinning the production of pollinator-friendly and receipt, and ultimately lead to better out-crossing varieties? The ultimate goal of CPR understanding, systems (Davis 2001). from the viewpoint of plant breeding, is the devel- The aspects of CPR relevant for breeding will vary opment of an assisted crossing strategy for exploiting depending on the objective—hybrid or population agronomic performance, e.g. heterosis. improvement. Hybrid programs should focus on matching both male and female sexual traits in the targeted environments where hybrid-seed production The contribution of CPR understanding is to occur. Population improvement or recurrent to plant breeding selection methods should focus on traits correlated with high levels of allogamy (Lewers and Palmer An understanding of CPR can provide potential tools 1997). An efficient and cost effective hybrid program to assist breeding methodologies, while at the same needs to target basic questions regarding the match- time preserving bee populations by developing spe- ing of female and male traits and consider traits cifically adapted cultivars. For this review, we will related to both pollen production and transfer, and to focus on legume improvement, both for hybrids and female function (Tregenza and Wedell 2000; Harder populations. Although CPR understanding is also et al. 2004). relevant to ‘‘on farm’’ and ‘‘in situ’’ conservation Patterns of pollinator visitation may limit crossing methodologies (Horneburg 2006), these are not among female and male plants. Pollinator foraging, considered in this paper. and thus pollen transfer, may occur only rarely Demonstration of heterosis for yield and other because the