A platform for soybean molecular breeding: the utilization of core collections for food security

Li-Juan Qiu 0 1 Li-Li Xing 0 1 Yong Guo 0 1 Jun Wang 0 1 Scott A. Jackson 0 1 Ru-Zhen Chang 0 1 0 S. A. Jackson Center for Applied Genetic Technology, University of Georgia , Athens, GA 30602, USA 1 L.-J. Qiu (&) L.-L. Xing Y. Guo J. Wang R.-Z. Chang The National Key Facility for Crop Gene Resources and Genetic Improvement (NFCRI), Institute of Crop Science, Chinese Academy of Agricultural Sciences , Beijing 100081, China Soybean is an important crop not only for human consumption but also for its addition of nitrogen to the soil during crop rotation. China has the largest collection of cultivated soybeans (Glycine max) and wild soybeans (Glycine soja) all over the world. The platform of soybean core, mini core and integrated applied core collections has been developed in the past decade based on systematic researches which included the sampling strategies, statistical methods, phenotypic data and SSR markers. Meanwhile, intergrated applied core collections including accessions with single or integrated favorite traits are being developed in order to meet the demand of soybean breeding. These kinds of core collections provide powerful materials for evaluation of germplasm, identification of trait-specific accessions, gene discovery, allele mining, genomic study, maker development, and molecular breeding. Some successful cases have proved the usefulness and efficiency of this platform. The platform is helpful for enhancing utilization of soybean genetic resources in sustainable crop improvement for food security. The efficient utilization of this platform in the future is relying on accurate phenotyping methods, abundant functional markers, high-throughput genotyping platforms, and effective breeding programs. - Food security exists when all people, at all times, have physical, social and economic access to sufficient, safe and nutritious food (FAO 2003). The sufficiency of human food is dependent in large on the availability and nutrient sufficiency of the plants consumed directly, or indirectly through animals (Bruulsema et al. 2012). Of the 7,000 plant species used worldwide in food and agriculture, only 30 crops feed the world, which provide 95 % of global plant-derived energy-intake (calories) and proteins (Schmidt and Wei 2006). The soybean is a crop of global importance and is one of the most frequently cultivated crops worldwide. It is important for both protein meal and vegetable oil and is used for both human and animal consumption as well as for industrial purposes, such as biofuels (Hartman et al. 2011). In addition, the soybean also plays an important role in crop diversification and benefits other crops due to its addition of nitrogen to the soil during crop rotation (Singh 2010). Soybean seeds contain about 20 % oil and 40 % protein. Of the oil fraction, 95 % is consumed as edible oil with the rest used for industrial products from cosmetics and hygiene products to paint removers and plastics. In addition, about 98 % of the soybean meal is used in livestock and aquaculture feeds due to its high protein level (Liu 2008). Soybeans are unique among crop plants in that they supply protein equal in quality to that of animal sources but with less saturated fat and no cholesterol (Young 1991). For this reason, soybeans have long been consumed in Asia and greatly increased in popularity outside of Asia as a primary source of protein in such traditional foods as tofu, soymilk, tempeh, natto, sprouts, green vegetable soybeans, and many others (www.soyinfocenter.com). Soybean was domesticated in China about 4,500 years ago, during the ancient Huangdi period (Qiu et al. 2011a). By the 16th century A.D. soybean was transported to Japan, Indonesia, Philippines and Vietnam, and later introduced to Europe and America (Hymowitz and Newell 1980). It is now cultivated in more than 60 countries across five continents. As the center of cultivated soybean (Glycine max), China has the most abundant genetic resources for soybean ([23,000 accessions) and its wild relatives, Glycine soja ([7,000 accessions). Chinese soybean germplasm is used widely throughout the world and these accessions are useful for small farmers that have to cope with heterogeneous microclimates and for advanced soybean improvement programs and to deal with needs in the future such as climate change. Although a large number of soybean accessions are now conserved either in various genebanks or in situ, \1 % of them have been used for breeding. In order to increase the efficiency of utilization of soybean genetic resources, different types of core collections have been developed from the whole collection of Chinese soybean germplasm, using a combination of passport data and morphological traits (Qiu et al. 2003; Song et al. 2010; Wang et al. 2006; Zhao et al. 2005). In this paper, the development and utilization of different core collections for Chinese soybean germplasm as a platform were reviewed. This platform is helpful for enhancing utilization of soybean genetic resources for sustainable crop improvement for food security (Fig. 1). The challenges and prospects of this platform for molecular breeding and food security were also discussed. Development of soybean core collections Plant germplasm is the lifeblood of plant breeding without which breeding is impossible to conduct. It is important that the diversity within major crops not only conserved but managed wisely and mined for useful traits. Although these abundant resources provide a rich genetic base for breeding, they also bring the difficulties for conservation and utilization. The approaches of core collection and mini core collection provided a rational approach to use a manageable number of accessions from large germplasm collections (Brown 1989; Frankel and Brown 1984; Upadhyaya and Oritz 2001). A core collection is a subset of accessions that represents the genetic diversity of a species and its relatives. Those samples not included in the core collections are not abandoned, but rather maintained as reserved collection, the total number of resources referred here is over 3,000 accessions, take 10 % core collections represent 70 % of the whole collection (Frankel and Brown 1984). A mini core collection consists of 10 % accessions of the core collection, and hence only 1 % of the entire collection (Upadhyaya and Oritz 2001). The mini core collection still represents the diversity of the entire collection but the number is largely reduced compared with that of core collection. Due to the reduced size, core collection and mini core collection could be studied extensively and the information derived can be used to guide more efficient utilization of the much larger reserved collection. Up to now, more than 35 core collections and mini core collections have been developed for nearly 30 species, including rice, wheat, maize, soybean, chickpea, peanut, common bean, and so on (Balfourier et al. 2007; Blair et al. 2009; Hao et al. 2008; Holb (...truncated)