Chromosome doubling by colchicine injection and haploidy induction in tropical genotypes of common and supersweet corn

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Abstract
The double-haploid technology in maize was developed in temperate environments, using germplasm and inducers adapted for these environments, with the aim of accelerating the obtaining of homozygous inbred lines. Therefore, to advance this technology in tropical environments, research involving germplasm and inducers adapted for this environment is necessary. The objectives were to determine the haploidy induction rate in tropical common and supersweet corn populations, employing a tropicalized gymnogenetic inducer population, and to identify the effectiveness of chromosome doubling by colchicine injection. The haploidy inducer PI4003 was used as a male parent and crossed with 25 tropical maize populations (23 common and two supersweet). The putative haploid seeds, classified by the R1-nj gene marker, were sown in trays with peat during the 2020/21 and 2021/22 harvest seasons, and 100 µL of a solution of 0.125% colchicine and 0.5% dimethyl sulfoxide was injected into each haploid seedling at the V2 stage. The next day, the treated seedlings were transplanted to an irrigated field. The PI4003 inducer presented a haploidy induction rate ranging from 0.9% to 5%. There were significant differences to tropical genotypes and harvests for survival rates, reproduction rates, and overall success rates. The overall success rate ranged from 2.9% to 34%. The chromosome doubling method by colchicine injection proved to be effective, with lower colchicine consumption per haploid seedling treated and a reduction in the generation of toxic waste for disposal.

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