Evaluation of soybean [Glycine max (L.) Merr.] genotypes for yield, water use efficiency, and root traits

Abstract

Drought stress has been identified as the major environmental factor limiting soybean [Glycine max (L.) Merr.] yield worldwide. Current breeding efforts in soybean largely focus on identifying genotypes with high seed yield and drought tolerance. Water use efficiency (WUE) that results in greater yield per unit rainfall is an important parameter in determining crop yields in many production systems, and is often related with crop drought tolerance. Even though roots are major plant organs that perceive and respond to drought stress, their utility in improving soybean yield and WUE under different environmental and management conditions are largely unclear. The objectives of this research was to evaluate soybean cultivars and breeding and germplasm lines for yield, WUE, root penetrability of hardpan, and root morphology. Field experiments were conducted at two locations in South Carolina (southeastern United States) during the 2017 cropping season to test the genotypes for yield and root morphology under irrigated and non-irrigated conditions. Two independent controlled-environmental experiments were conducted to test the genotypes for WUE and root penetrability of synthetic hardpans. The slow wilting lines NTCPR94-5157 and N09-13890 had equal or greater yield than the checks- cultivar NC-Raleigh and the elite South Carolina breeding line SC07-1518RR, under irrigated and non-irrigated conditions. The high yielding genotypes NTCPR94-5157, N09-13890, and SC07-1518RR exhibited root parsimony (reduced root development). This supported the recent hypothesis in literature that root parsimony would have adaptational advantage to improve yield under high input field conditions. The high yielding genotypes NTCPR94-5157, N09-13890, NC-Raleigh, and SC07-1518RR and a cultivar Boggs (intermediate in yield) possessed high WUE and had increased root penetrability of hardpans. These genotypes offer useful genetic materials for soybean breeding programs for improving yield, drought tolerance, and/or hardpan penetrability.

Fig 1. The mesocosms used to grow soybean plants in the experiment.

Mesocosms were constructed of two stacked polyvinyl chloride (PVC) columns with an inside diameter of 15 cm. The height of the bottom and top columns were 46 and 25 cm, respectively. Each mesocosm was sealed at the bottom with a plastic cap, which had a central hole of 0.5 cm diameter for drainage. A diagram and a photograph of a mesocosm that contained a synthetic hardpan in between the top and bottom columns (A and B, respectively). The synthetic hardpan was made up of paraffin wax and petroleum jelly, and had a diameter of 20 cm and thickness of 2 cm. A diagram and a photograph of a mesocosm that did not contain a synthetic hardpan (C and D, respectively). The top and bottom columns along with the synthetic hardpan in between (if the mesocosm contained one) were tightly sealed together with a duct tape as shown in Fig 1B and 1D.

Fig 2

Daily maximum (Tmax) and minimum (Tmin) temperatures from planting through the end of the season at Florence, SC, USA (a) and Pendleton, SC, USA (b). Temperature data were obtained from the National Centers for Environmental Information (NCEI) of National Oceanic and Atmospheric Administration (NOAA). Soybean genotypes were planted on 9 June 2017 at Florence and 8 June 2017 at Pendleton. The duration of the crop season was 188 and 161 d at Florence and Pendleton, respectively.

Fig 3

Daily precipitation and irrigation from planting through the end of the season at Florence, SC, USA (a) and Pendleton, SC, USA (b). Precipitation data were obtained from the National Centers for Environmental Information (NCEI) of National Oceanic and Atmospheric Administration (NOAA). Soybean genotypes were planted on 9 June 2017 at Florence and 8 June 2017 at Pendleton. The duration of the crop season was 188 and 161 d in Florence and Pendleton, respectively. Irrigation involved application of 25.4 mm water at 35, 56, 69, 76, and 83 days after planting (DAP) at Florence and application of 25.4 mm water at 102 DAP at Pendleton.

Fig 4

Seed yield of soybean genotypes grown at Florence, SC, USA under irrigated and non-irrigated conditions (Fig a and b, respectively) and at Pendleton, SC, USA (Fig c). Irrigated plots received 25.4 mm water at 35, 56, 69, 76, and 83 days after planting (DAP) at Florence and 25.4 mm water at 102 DAP at Pendleton. However, the genotype-by-irrigation interaction effect was not significant on yield at Pendleton. Therefore, data were averaged across irrigation treatments for this location. Bars represent least square means and error bars represent standard errors. Least square means with different letters are significantly different according to the LSD test at P < 0.05.