Soybean cultivars are extremely diverse in time to flowering and maturation as a result of various photoperiod sensitivities. The underlying molecular genetic mechanism is not fully clear, however, four maturity loci E1, E2, E3 and E4 have been molecularly identified. In this report, cultivars were selected with various photoperiod sensitivities from different ecological zones, which covered almost all maturity groups (MG) from MG 000 to MG VIII and MG X adapted from latitude N 18° to N 53°. They were planted in the field under natural daylength condition (ND) in Beijing, China or in pots under different photoperiod treatments. Maturity-related traits were then investigated. The four E maturity loci were genotyped at the molecular level. Our results suggested that these four E genes have different impacts on maturity and their allelic variations and combinations determine the diversification of soybean maturity and adaptation to different latitudes. The genetic mechanisms underlying photoperiod sensitivity and adaptation in wild soybean seemed unique from those in cultivated soybean. The allelic combinations and functional molecular markers for the four E loci will significantly assist molecular breeding towards high productivity.

Wild soybean is a typical short-day plant that begins flowering when the days are shorter than its critical photoperiod. Soybean was domesticated in the temperate region of East Asia at the relatively high latitude, and the breeding and release of soybean varieties have historically centered on mid-and high-latitude temperate regions. Low-latitude areas with tropical and subtropical climates were previously considered unsuitable for soybean production because most temperate soybean varieties exhibited precocious flowering and early maturity and suffered from low yields. The discovery and introduction of the long juvenile trait into soybean varieties in the 1970s (Hartwig and Kiihl, 1979) fundamentally changed global soybean production in a way that has had an enormous influence on commodity markets. This trait delays flowering and thereby ensures sufficient vegetative growth prior to the developmental transition to reproductive growth. The long juvenile trait thus solved the early maturation and low yield problems that had hitherto prevented economically viable soybean production in lowlatitude regions (Destro et al., 2001). The United States and Brazil pioneered the introduction of the long juvenile trait in low-latitude soybean breeding programs. Brazil has expanded its soybean production enormously, from 1 million hectares in 1970 (Brown, 2004) to over 33 million hectares in 2016 (http:// gain.fas.usda.gov/Recent%20GAIN%20Publications/Oilseeds %20and%20Products%20Update_Brasilia_Brazil_12-1-2016. pdf).