Characterizing the Soybean Nested Association Mapping Population (SoyNAM) Parental Lines for Physiological Traits Associated with Yield.

The soybean (Glycine max) gene pool in North America is quite narrow with only 17 accessions contributing to 86% of the parentage of modern cultivars. The Soybean Nested Association Mapping population (SoyNAM) was developed by crossing 40 diverse genotypes from maturity groups (MG) 1 through 5 with a common MG 3 parent to develop 40 recombinant inbred populations with the objective of diversifying the soybean gene pool. These populations were genotyped with molecular markers and characterized for yield, disease, maturity and a few other important traits. This study focuses on identifying the extreme genotypes by characterizing the SoyNAM parental lines for yield and drought related traits that have not been mapped extensively or previously. The experiment was conducted in 2015 and 2016, at Fayetteville, Arkansas with four replications. Canopy coverage was estimated through aerial digital images taken 3-4 times until full canopy closure. After canopy closure, two biomass harvests from 1m² area were made at two-week intervals to determine radiation use efficiency(RUE), nitrogen fixation, shoot nitrogen and ureide concentration. During seed filling, two harvests starting at mid-R5 and two weeks later were used to calculate seed growth rate (SGR). Yield was determined from a bordered section of each plot at maturity. Two-years of data indicated that LD01-5907 had slow SGR, long seed fill duration, high yield and high harvest index. Genotype LG97-7012 had high average seed weight, high HI, and high nitrogen and ureide concentration. Similarly, LG04-4717, Skylla and PI 404.188A had high RUE as well as high nitrogen fixation. This is similar to previous reports that indicated that traits like high N2 fixation rate, SGR, and a long SFD are associated with high yields under maximum-yield conditions. Identification of most divergent parental lines for such traits will aid in selecting RIL populations for future QTL mapping studies.