Yield and water-use related traits in landrace and new soybean cultivars in arid and semi-arid areas of China

Empirical soybean breeding has improved its yield in arid and semi-arid areas of China. The objective of this study was to identify the important traits found in successful commercial soybean cultivars following the domestication of landraces through breeding in the semi-arid region of North-west China. A further objective was to identify any key traits that can be targeted using trait-based selection to improve yield under drought. Seed yield, phenology, water-use, water-use efficiency and their related traits in soybean landraces and successful cultivars were compared over a four year period in the field and this was supplemented with an outdoor pot experiment. The results in both field and pot experiments showed that successful soybean cultivars have a reduced thermal time to flowering but the thermal time for seed filling has increased. This change in partitioning of phenological time in the commercial cultivars resulted in a lower number of pods, fewer seeds per unit area but an increase in 100-seed weight, harvest index and seed yield. New soybean cultivars with high seed yield also had a lower vegetative biomass and less water use in both field and pot experiments than landraces but the lower water use did not compromise seed yield. The commercial cultivars also had a lower pod wall ratio (ratio of pod wall weight to total pod weight at maturity) which also contributed to yield by improving harvest index. We conclude that the key traits that have been altered as a result of soybean breeding in arid and semi-arid areas of China have been (1) a shortening of the duration between sowing and flowering but an extension of the seed filling period, (2) fewer pods but an increase in seed number per pod and 100-seed weight and also a decreased pod wall ratio, (3) an increased harvest index and (4) a reduced water use, particularly in the deeper soil layers.