Peer review

The paper refers to spring wheat breeding for potential yield, yield in the absence of manageable stresses, under irrigated low latitude conditions, representing a major environment for wheat production. Initially it discusses two propositions both over 50 years old. Donald argued that for greater yield, early generation selection should target uncompetitive plant traits or ?communal? plants. In contrast, Fasoulas proposed the opposite, namely selection of plants with high yield under nil-competition, aided by the use of a honeycomb design to control for soil variation. Despite some promising results, the absence of definitive proof of the relevance to yield breeding of either concept, wheat breeders have generally opted for an intermediate approach with focus on measuring yield in plots as early as possible. They have been successful but yield progress is slowing. The advent of seeding machinery permitting regular planting patterns through seed singulation, and the reporting of optimal densities for maximum yield per hectare as low as 20 plants/m2 under irrigation and excellent management in northwest Mexico (Fischer et al., 2019), suggest that Fasoulas's method needs reinvestigating at least for wheat. Yield crossovers (i.e. genotype rank changes) with increasing plant density from the very low density for nil-competition (around 1.4/m2) are expected to be less likely if the target crop density is as low as say 20/m2. There are enough unknowns in the physiology of the wheat crop response to density to suggest that this is quite possible. The approach opens up new possibly more efficient strategies for early generation (e.g. F2) selection for potential yield and could give greater yield progress per unit cost. It would be especially suited for hybrid wheat breeding and production systems. Finally the paper discusses, in the light of the advances in precision agriculture, the opportunities for the agronomy of crops and breeding-nurseries based on low-density honeycomb planting. The major challenge, namely weed control, is manageable.

The northwest Mexican wheat research reported here was supported by the International Maize and Wheat Improvement Center (CIMMYT), and the thinking time by the Commonwealth Scientific and Industrial Research Organization (CSIRO).

Text in English