Symmetric response to competition in binary mixtures of cultivars associates with genetic gain in wheat yield

Abstract

The evolution in the definition of crop yield—from the ratio of seed harvested to seed sown to the contemporary measure of mass of seed per unit land area―has favoured less competitive phenotypes. Here we use binary mixtures of cultivars spanning five decades of selection for yield and agronomic adaptation to ask three questions. First, what is the degree of symmetry in the response of yield to neighbour; this is, if an older, more competitive cultivar increases yield by 10% with a less competitive neighbour in comparison to pure stands, would the newer, less competitive cultivar reduce yield by 10% when grown with older neighbour. Lack of symmetry would indicate factors other than competitive ability underly yield improvement. Second, what are the yield components underlying competitive interactions. Third, to what extent are the responses to neighbour mediated by radiation, water and nitrogen. A focus on yield components and resources can help the interpretation of shifts in the crop phenotype in response to selection for yield. The rate of genetic gain in yield over five decades was 24 kg ha−1 year−1 or 0.61% year−1. A strongly symmetrical yield response to neighbour indicates that yield improvement closely associates with a reduction in competitive ability. Response to neighbour was larger for grain number and biomass than for grain weight and allocation of biomass to grain. Under our experimental conditions, competition for radiation was dominant compared to competition of water and nitrogen. High‐yielding phenotypes had lower competitive ability for radiation but compensated with higher radiation use efficiency, a measure of canopy photosynthetic efficiency. Genetic and agronomic manipulation of the crop phenotype to reduce competitive ability could further improve wheat yield to meet the challenge of global food security.

Explaining pre-emptive acclimation by linking information to plant phenotype

“…For crops, yield does not normally scale from single plant to stand ( Pedró et al , 2012 ), and for natural vegetation, distribution of plant species in most cases cannot be predicted from survival of plants growing in isolation. Although neighbours are in both cases important, there are differences between wild plants and crops in their responses to them as nature selected for but agriculture selected against competitive ability ( Denison, 2012 ; Weiner et al , 2017 ; Weiner, 2019 ; Cossani and Sadras, 2021 ). In addition, compared with crop stands, natural vegetation is often more diverse, leading to more complex interactions.…”

High yield with efficient nutrient use: Opportunities and challenges for wheat

“… 7 The increase in shoot biomass in Australian varieties is associated with higher radiation use efficiency with no apparent changes in leaf photosynthesis or respiration. 8 Using crop physiology to inform biotechnology, Calderini et al. (2021) successfully overcame the trade-off between grain weight and grain number per m 2 by promoting the ectopic expression of expansions in developing wheat seeds.…”

Competitiveness of Early Vigour Wheat (Triticum aestivum L.) Genotypes Is Established at Early Growth Stages

“…This was remedied, in part, by the introduction of the reduced height (Rht1 and Rht2) mutations during the 1960s with the advent of the Green Revolution. While the resulting semi-dwarf cultivars significantly improved yields, they were generally considerably less vigorous [17] and less competitive than their taller parents [40]. Nevertheless, semi-dwarf varieties do exhibit variation in early shoot vigour, and this is most commonly screened for by measuring the size of the first few leaves [26,27].…”