Fig. 1

Development of the CUBIC population. The present CUBIC population, consisting of 1404 progenies, was derived from 24 elite Chinese maize inbred lines. a These 24 founders were crossed under a Complete Diallel Cross type IV (CDC IV) mating design, omitting parents and reciprocal crosses. Thirty F₁s with best agronomic performance (early flowering time, small ear height, and big ear size) were selected to further cross in the CDC IV design. b Another 110 F₁s were randomly selected for open pollination in isolation. Two hundred and 400 ears were harvested from the agronomically selected and randomly selected subsets, respectively, and seeds from the above F₁s were mixed together in a 2:1 ratio with the expectation of improving population performance and maximizing diversity. c The resulting individuals were planted under open pollination in isolation for 6 generations. About 2000 ears of the most diverse lines were retained and mixed equally in each generation. Finally, the population was self-pollinated by single seed descent for another 6 generations, and a total of 1664 inbred lines were obtained, of which 1404 have been successfully sampled and sequenced, and thus used in further analysis