Juliana Moraes Machado de Oliveira

Chromosomal doubling of haploids, through exposure to antimitotic agents for specific periods, is crucial for obtaining doubled haploids. The objectives of this study were (a) to determine the potential for chromosome doubling by immersing the roots of haploid super sweet corn ( Zea mays L. var. saccharata ) seedlings at 17°C in solutions of colchicine, pronamide, and amiprophos‐methyl + pronamide for different exposure times; and (b) to compare the doubling effectiveness of these antimitotic solutions, for different exposure times at greenhouse and field cultivation. Putative haploid seeds from eight super sweet populations, obtained by crossing with the hybrid inducer CIM2GTAIL‐P1 × CIM2GTAIL‐P2, were used. The first experiment used exposure times of 5–12 h for colchicine and pronamide solutions and 5–16 h for amiprophos‐methyl at 17°C. In the second experiment, exposure times of 5, 6, and 7 h were chosen for pronamide and amiprophos‐methyl solutions, and 10, 11, and 12 h for colchicine, at 17°C. The hybrid inducer promoted a mean real haploid induction rate of 9.7%. Greenhouse treatments promoted greater success in obtaining doubled haploids. The pronamide solution led to greater lethality of seedlings but obtained mean overall success rates of 11.2%–12.7%, not differing from treatments using a solution containing amiprophos‐methyl. Colchicine treatment with 10 h of exposure at 17°C resulted in the best performance, with overall success rates of 32.3% in the greenhouse and 20.3% in the field, making it the best treatment for obtaining DHs in super sweet corn.

Doubled haploid technology accelerates the development of fully homozygous maize lines compared with conventional selfing. However, specific protocols for supersweet corn ( Zea mays L . var. saccharata ), particularly regarding immersion time in antimitotic solutions and temperature during chromosome doubling, remain poorly defined. This study investigated haploid induction rates in supersweet corn with a tropicalised haploid inducer hybrid and evaluated the effects of temperature and immersion time across three antimitotic solutions in an adapted newly germinated seeds method for chromosome doubling. Survival rate was assessed in diploid seeds immersed in water at 0°C, 17°C and 25°C and in haploid seeds treated with water at 0°C and 17°C, as well as with colchicine, pronamide and amiprophos‐methyl combined with pronamide, at 17°C under different immersion durations. Chromosome doubling efficiency of putative haploid was compared among the newly germinated seed treatments and with the root immersion method in colchicine. The tropical inducer hybrid showed an average haploid induction rate of 14.6%. Temperature and exposure time strongly affected survival and overall protocol feasibility, and 17°C emerged as the most suitable temperature by enabling longer exposure to antimitotic agents while maintaining higher survival. Treatments with 10 h in pronamide and 12 h in amiprophos‐methyl plus pronamide increased chromosome doubling but caused high mortality, indicating that shorter exposures are more suitable. Water treatment at 0°C did not improve chromosome doubling efficiency. These results demonstrate that herbicide‐based immersion of newly germinated seeds at 17°C is a promising alternative for chromosome doubling in tropical supersweet corn.

Colchicine is a widely used and effective agent for producing doubled haploid inbred lines in maize. However, its high toxicity and cost have prompted the search for safer and more economical alternatives for chromosome doubling. This study aimed to evaluate the effectiveness of pronamide and amiprophos‐methyl solutions as alternatives to colchicine for chromosome doubling in tropical white corn (Zea mays L.), to identify the potential for spontaneous chromosomal doubling in tropical white maize populations, and to compare the haploid induction rates of three tropicalized inducer lines (CIM2GTAIL‐P1, CIM2GTAIL‐P2, and CIM2GTAIL‐P3) along with their three hybrid combinations in crosses with tropical white corn. Eight populations of white corn were pollinated by six inducer genotypes, and the haploid induction rates were estimated. At the V2 stage, the roots of the haploid seedlings were washed and immersed in four treatments for chromosome doubling: a negative control with water, an amiprofos‐methyl and pronamide solution, a colchicine solution, and a pronamide solution. Parameters such as self‐pollination rate, self‐pollination efficiency, survival, reproduction, and overall success were estimated. The amiprofos‐methyl and pronamide treatment proved to be an effective alternative for the production of doubled haploid lines in tropical white corn, successfully replacing the use of colchicine. The tropical white corn populations presented spontaneous chromosome doubling rates ranging from 7.9% to 38.3%. The CIM2GTAIL‐P1 × CIM2GTAIL‐P2 hybrid demonstrated the highest haploid induction rate, with an average of 12.9%.

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.

A produção de milho superdoce brasileira é preponderantemente destinada as indústrias de conservas, que necessitam de elevada produtividade, uniformidade e qualidade de produção, oferecidas pelas cultivares híbridas de linhagens. A tecnologia duplo-haploide (DH) está sendo utilizada para reduzir o tempo de produção de linhagens completamente homozigotas e melhor explorar a heterose em combinações híbridas em milho comum, mas ainda pouco estudada em milho superdoce. Os objetivos foram determinar o potencial de linhagens DHs de milho superdoce na síntese de híbridos; identificar linhagens DHs elites para uso como testadoras em cruzamento top crosses; determinar o tipo predominante de ação gênica para características importantes no melhoramento de milho superdoce e suas correlações. As 29 combinações entre linhagens DHs de quatro populações superdoce e seis testemunhas foram avaliadas na Fazenda Escola/UEL, durante as safras 2019/2020 e 2020/2021, empregando o delineamento de blocos casualizados, com 3 repetições. As características avaliadas foram: produtividades de espigas com e sem palha, produtividadede grãos; alturas de plantas e de espigas; comprimento e diâmetro de espigas; número de fileiras de grãos nas espigas; padrão agronômico e grau Brix. Houve efeito significativo de safras todas as características, sendo a safra 2020/2021 a melhor para produtividade. A interação tratamento x safra foi observada apenas para diâmetro de espiga e padrão agronômico. Na média das duas safras, 38% dos híbridos do dialelo foram superiores em relação às testemunhas comerciais, que ficaram agrupadas junto à média do restante dos híbridos avaliados. As linhagens L1 e L5 apresentaram as maiores estimativas de capacidade geral de combinação para as características de produtividades de espigas com palha, sem palha e de grãos, com valores iguais a 2244 e 2627; 1260 e 1388; 811 e 1000 kg ha-1, respectivamente, sendo candidatas para uso como testadoras em trabalhos futuros. Entre os híbridos mais produtivos, as maiores estimativas de capacidade específica para produtividades de espigas com palha, sem palha e de grãos foram observadas para os híbridos HA5, HB2 e HC12, com valores entre 4685 e 1947, 2829 e 1329, 1680 e 1095 kg ha-1, respectivamente. Foi verificado que as ações gênicas aditivas e não aditivas foram importantes para a maioria das características avaliadas. A característica produtividade de espigas sem palha é a que mais se correlaciona com produtividade de grãos, podendo ser utilizada para a seleção de genótipos mais produtivos para a produção de milho em conserva.