Broadening the Genetic Base of Soybean: A Multidisciplinary Approach

Abstract

Soybean [Glycine max (L.) Merr.] is an economically important legume with 2n = 40 chromosomes, whose seeds contain an average of 40% protein and 20% oil, and its plants enrich the soil by fixing nitrogen in symbiosis with nitrogen-fixing bacteria. World soybean production has doubled in the past twenty years to over 220 million metric tons in 2006; the producing countries are U.S.A., Brazil, Argentina, China, and India. Soybean was domesticated in East Asia from its wild annual progenitor G. soja Sieb. & Zucc. (2n = 40). There are 26 wild perennial species, indigenous to Australia, of the subgenus Glycine but a common progenitor with 2n = 20 chromosomes has not been identified, and it may be extinct. It has been demonstrated that Glycine species are of either of allo-or auto-tetraploid origin. The cytogenetic knowledge of soybean lags far behind that of other model important crops (rice, maize, wheat, tomato), because it's somatic chromosomes are symmetrical, and only one pair of satellite chromosomes can be identified. Pachytene chromosome analysis created a chromosome map that has laid the foundation for producing primary trisomics. Several molecular linkage maps have been developed, but only 11 of the 20 molecular linkage groups (MLGs) have been associated with specific chromosomes. The genetic base of modern soybean cultivars is narrow and soybean breeders are confined to crossing within the primary gene pool (GP-1). Soybean does not have secondary gene pool (GP-2). Exploitation of the tertiary and quaternary gene pools (GP-3, GP-4) has been attempted but ended at the amphidiploid stage. A methodology for producing fertile lines derived from G. max and G. tomentella (2n = 78) cross has been developed, thereby making introgression of useful genes from GP-3. Genetic transformation has produced Roundup Ready® Soybeans, resistant to glyphosate herbicide.