Effect of F1 and F2 generations on genetic variability and working steps of doubled haploid production in maize
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For doubled haploid (DH) production in maize, F-1 generation has been the most frequently used for haploid induction due to facility in the process. However, using F-2 generation would be a good alternative to increase genetic variability owing to the additional recombination in meiosis. Our goals were to compare the effect of F-1 and F-2 generations on DH production in tropical germplasm, evaluating the R1-navajo expression in seeds, the working steps of the methodology, and the genetic variability of the DH lines obtained. Sources germplasm in F-1 and F-2 generations were crossed with the tropicalized haploid inducer LI-ESALQ. After harvest, for both induction crosses were calculated the haploid induction rate (HIR), diploid seed rate (DSR), and inhibition seed rate (ISR) using the total number of seeds obtained. In order to study the effectiveness of the DH working steps in each generation, the percentage per se and the relative percentage were verified. In addition, SNP markers were obtained for genetic variability studies. Results showed that the values for HIR, ISR, and DSR were 1.23%, 23.48%, and 75.21% for F-1 and 1.78%, 15.82%, and 82.38% for F-2, respectively. The effectiveness of the DH working step showed the same percentage per se value (0.4%) for F-1 and F-2, while the relative percentage was 27.2% for F-1 and 22.4% for F-2. Estimates of population parameters in DH lines from F-1 were higher than F-2. Furthermore, population structure and kinship analyses showed that one additional generation was not sufficient to create new genotype subgroups. Additionally, the relative efficiency of the response to selection in the F-1 was 31.88% higher than F-2 due to the number of cycles that are used to obtain the DH. Our results showed that in tropical maize, the use of F-1 generation is recommended due to a superior balance between time and genetic variability.
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