The relationship between competitive ability and yield stability in an old and a modern winter wheat cultivar

This study was conducted to determine if there were differences in competitive ability and yield stability on the growth of an old landrace of winter wheat (Triticum aestivum), Pinglang 40 (PL40), and a modern cultivar, Changwu135, (CW135), which differed in time of cultivar release, height, shoot and root biomass. A second aim was to investigate whether there is a relationship between competitive ability and yield stability. One pot and two field experiments were conducted to monitor changes in the competitive ability and yield stability of an old and a modern winter wheat cultivar grown in monoculture and mixtures using a de Wit replacement series. The pot study was conducted at two soil moisture levels: (a) well watered (WW), soil maintained at 85% field capacity, and (b) moderate drought (MD), soil maintained at 55% field capacity. The field experiments were conducted in 2 years that were drier than the average. In the second field experiment 40 mm of irrigation was applied to half of the plots at jointing, booting and anthesis. The results were similar in the pot and field experiments. In the mixture, the old cultivar PL40 had a greater relative yield with a larger number of spikes per plant when compared with those of the modern cultivar CW135. The dry matter per stem of CW135 tended to decrease with the increasing proportion of PL40, indicating a lower competitive ability of the modern cultivar than that of the old cultivar. The superior competition of PL40 was primarily due to the higher plant height, larger leaf area index, greater tillering capacity and larger root system. Our results showed that the modern cultivar CW135 produced a higher grain yield, yield components (except spike number), water use efficiency (WUE_g) and harvest index under both water regimes in monoculture. However, the reduction in grain yield of CW135 when subjected to water-limited conditions was less than that of PL40 in the pot and field experiments. The greater grain yield of the CW135 was associated with a higher harvest index, thousand-kernel-weight and a lower root:shoot ratio. Water consumption over the entire growing period was significantly lower in CW135 under all soil moisture conditions, and the main difference in water consumption between the two cultivars was observed before anthesis. Post-anthesis accumulation of dry matter was greater in CW135 under water-limited conditions, but there was no difference between cultivars when water was adequate. The dry matter remobilization and contribution to grain yield of CW135 was lower than that of PL40. The results of the present study demonstrated that the higher competitive ability in the old landrace led to an increased sensitivity to environmentally-induced stress. As a result, there was a greater loss in grain yield by the old cultivar when the water supply was unfavorable. In addition, the differences in the life history strategy between the old and modern cultivars imply that reducing competitive ability in the modern cultivar has led to increased yield of the crop population and greater yield stability.