The ‘Minibulk’ system for advancing winter cereal breeding populations

Authors: OLSON, ERIC - Michigan State University; Brown-Guedira, Gina; NOBLE, AMANDA - Michigan State University; Smith, Jared; FORSBERG, LANCE - Michigan State University; BRISCO-MCCANN, ELIZABETH - Michigan State University

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2022
Publication Date: 2/3/2022
Citation: Olson, E., Brown Guedira, G.L., Noble, A., Smith, J.H., Forsberg, L., Brisco-Mccann, E. 2022. The ‘Minibulk’ system for advancing winter cereal breeding populations. Crop Science. 62:1011-1023. doi.org/10.1002/csc2.20718.
DOI: https://doi.org/10.1002/csc2.20718

Interpretive Summary: Cultivars of common wheat (Triticum aestivum L.) are highly inbred. Although winter wheat is an annual crop, it has a relatively long generation time due the requirement of a cold treatment to induce flowering. Conventional selected-bulk breeding for developing new cultivars is a low cost means of advancing populations but requires several years of selection in the field to generate fixed lines. Doubled haploid methods produce fixed lines quickly but without selection and at high cost. The ‘minibulk’ system was developed to combine the speed of doubled haploids with the population size and crossover opportunities of selected-bulk breeding. Breeding populations of winter wheat were vernalized and advanced at high density in the greenhouse for three generations. The resulting F4 populations underwent visual selection in the field. During vernalization, seeds in all populations germinated and underwent vegetative growth forming a dense seed mat that was transplanted directly into greenhouse pots. A 22-hour photoperiod accelerated development and many populations reached physiological maturity as soon as five weeks after transplanting. Increasing the number of seeds planted from 300 in the F2 to 500 in the F3 increased the number of the number of fertile spikes produced thereby maintaining a larger population size. Adoption of the minibulk system by winter cereal breeding programs can lead to significant cost savings and acceleration of the breeding cycle.

Technical Abstract: Conventional selected-bulk breeding is a low cost means of advancing populations but requires years of selection in the field to generate fixed lines. Doubled haploid methods produce fixed lines quickly but without selection and at high cost. The ‘minibulk’ system was developed to combine the speed of doubled haploids with the population size and crossover opportunities of selected-bulk breeding. Breeding populations of winter wheat (Triticum aestivum L.) were vernalized and advanced at high density in the greenhouse from the F2 to the F4 generation. F4 populations underwent visual selection in the field and derived lines were genotyped for variants at photoperiod and vernalization alleles and across the genome using genotyping-by-sequencing. The number of crossover events and parental genome contributions were determined for RILs within populations and among RILs across populations. During vernalization, seeds in all populations germinated and underwent vegetative growth forming a dense seed mat that was transplanted directly into greenhouse pots. A 22-hour photoperiod accelerated development and many populations reached physiological maturity as soon as five weeks after transplanting. Increasing the number of seeds planted from 300 in the F2 to 500 in the F3 increased the number of the number of fertile spikes produced thereby maintaining a larger population size. The number of crossovers detected differed significantly between populations and chromosomes while the number of crossovers detected in each population was related to marker density. Adoption of the minibulk system by winter cereal breeding programs can lead to significant cost savings and acceleration of the breeding cycle.