Wild Relatives of Maize, Rice, Cotton, and Soybean: Treasure Troves for Tolerance to Biotic and Abiotic Stresses

Abstract

Global food demand is expected to nearly double by 2050 due to an increase in the world's population. The Green Revolution has played a key role in the past century by increasing agricultural productivity worldwide, however, limited availability and continued depletion of natural resources such as arable land and water will continue to pose a serious challenge for global food security in the coming decades. High yielding varieties with proven tolerance to biotic and abiotic stresses, superior nutritional profiles, and the ability to adapt to the changing environment are needed for continued agricultural sustainability. The narrow genetic base of modern cultivars is becoming a major bottleneck for crop improvement efforts and, therefore, the use of crop wild relatives (CWRs) is a promising approach to enhance genetic diversity of cultivated crops. This article provides a review of the efforts to date on the exploration of CWRs as a source of tolerance to multiple biotic and abiotic stresses in four global crops of importance; maize, rice, cotton, and soybean. In addition to the overview of the repertoire and geographical spread of CWRs in each of the respective crops, we have provided a comprehensive discussion on the morphological and/or genetic basis of the traits along with some examples, when available, of the research in the transfer of traits from CWRs to cultivated varieties. The emergence of modern molecular and genomic technologies has not only accelerated the pace of dissecting the genetics underlying the traits found in CWRs, but also enabled rapid and efficient trait transfer and genome manipulation. The potential and promise of these technologies has also been highlighted in this review.

Keywords: cotton; crop wild relatives (CWRs); maize; rice; soybean; tolerance to abiotic stress; tolerance to biotic stress.

Figure 1

Centers of origin and primary geographical distribution of cultivated maize and its wild relatives. Information on the distribution and centers of origin was gathered from Wilkes (1977), Doebley (1983), Iltis and Benz (2000), and Standley (2015). International Maize and Wheat Improvement Center (CIMMYT) (https://www.cimmyt.org/) is a major maize “living catalog of genetic diversity comprising over 28,000 unique seed collections of maize,” including teosinte species. In addition to CIMMYT, seeds of maize, teosinte, and Tripsacum species are stored and could be obtained from the Germplasm Resources Information Network in Beltsville, USA (https://npgsweb.ars-grin.gov/gringlobal/search.aspx) and N. I. Vavilov Research Institute of Plant Industry in Saint Petersburg, Russia (http://www.vir.nw.ru/).

Figure 2

Centers of origin and/or primary sites of diversity and distribution of wild relatives of Rice. South East Asia (S.E. Asia), a key region for the origin and distribution of several wild relatives of Rice, is indicated by a dotted line. Information on the distribution and centers of origin was gathered from Shakiba and Eizenga (2014), and references therein. “The International Rice Genebank, maintained by International Rice Research Institute, holds more than 124,000 rice accessions that include modern and traditional varieties and wild relatives of rice. It is the biggest collection of rice genetic diversity in the world. Countries from all over the world have sent their rice samples to IRRI for safe keeping as well as for sharing” (http://irri.org/). In addition to IRRI, the Germplasm Resources Information Network in Beltsville, USA (https://npgsweb.ars-grin.gov/gringlobal/search.aspx) also stores and distributes genetic material of cultivated rice and its wild relatives.

Figure 3

(AB) Centers of origin or primary geographic distribution sites of cultivated cotton species G. hirsutum L. (A), G. barbadense L (A), G. arboreum L. (B), and G. herbaceum L. (B), and their wild relatives (A,B). Information on the distribution and centers of origin was gathered from Fryxell (1992) and Wendel and Cronn (2003). Seeds of cotton and its wild relatives are stored and could be obtained from the Germplasm Resources Information Network in Beltsville, USA (https://npgsweb.ars-grin.gov/gringlobal/search.aspx).

Figure 4

Centers of origin and primary geographical distribution of cultivated soybean and its wild relatives. Information on the distribution and centers of origin was gathered from Brown et al. (1989), Sherman-Broyles et al. (2014), Zhou et al. (2015). The Germplasm Resources Information Network in Beltsville, USA (https://npgsweb.ars-grin.gov/gringlobal/search.aspx) stores large global collection of soybean cultivars. Commonwealth Scientific and Industrial Research Organization in Canberra, Australia, encompasses a major collection of wild Glycine species.