Abstract
For doubled haploid (DH) production in maize, F1 generation has been the most frequently used for haploid induction due to facility in the process. However, using F2 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 F1 and F2 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 F1 and F2 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 F1 and 1.78%, 15.82%, and 82.38% for F2, respectively. The effectiveness of the DH working step showed the same percentage per se value (0.4%) for F1 and F2, while the relative percentage was 27.2% for F1 and 22.4% for F2. Estimates of population parameters in DH lines from F1 were higher than F2. 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 F1 was 31.88% higher than F2 due to the number of cycles that are used to obtain the DH. Our results showed that in tropical maize, the use of F1 generation is recommended due to a superior balance between time and genetic variability.
Highlights
Developing doubled haploid (DH) lines in maize has become a common practice in public and private institutions worldwide because of the gain of time in plant breeding programs
haploid induction rate (HIR) of source germplasm ranged from 0.77% to 3.76%, and the highest values were observed for genotype 30F53H in both generations
Considering the results showed in each working step, we present below some estimates related to the number of seeds that should be induced with the tropical inducer line LI-ESALQ to obtain 100 DH
Summary
Developing doubled haploid (DH) lines in maize has become a common practice in public and private institutions worldwide because of the gain of time in plant breeding programs. DH methodology includes the following steps: 1) induction of maternal haploids by crossing an inducer line with a donor genotype, 2) identification of haploids at the seed or seedling stage, 3) chromosome doubling of putative haploids selected, 4) self-pollination of the D0 plants to obtain D1 lines [1], and 5) multiplication of D1 lines to be introduced into the breeding program. The constant use of F1 generation over selection cycles could result in a decreased response to selection due to a lower recombination rate in the DH lines compared to the maize lines obtained from the recombinant population [4,5]. Each generation and synthetic population used in the DH process has advantages and disadvantages in the maize breeding. Studies reporting this question are related to temperate maize germplasm or computational simulations [6,7]
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