Effect of F1 and F2 generations on genetic variability and working steps of doubled haploid production in maize

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.

Breeding strategies for tropical maize targeting in vivo haploid inducers

“…Moreover, the discrepancy between HIR in 2012/2013 and 2014/2015 can be explained by natural selection disfavoring the haploidy-inducing gametes during selfing. From an evolutionary point of view, a higher proportion of haploids in the family caused by high HIR of the pollinator would result in reduced plant vigor, because haploid maize plants are less vigorous, often male sterile, and therefore generally less likely to produce progenies than diploid maize plants (Couto et al 2020), which explains the action of natural selection (Prigge et al 2012). The latter may also explain the difficulties of maintaining haploid inducers described by maize breeders.…”

“…Maize haploid inducer lines, when used as pollinators, trigger the production of seeds with a haploid embryo at a mean rate of 8% due to a hetero-fertilization together with failed egg-sperm cell fusion (Tian et al 2018). In spite of the successful development of maize haploid inducers in the tropics (Chaikam 2012, Couto et al 2020), compared to temperate conditions, data on this DH process are still scarce.…”

“…Moreover, specifically the use of binomial models has been intensified in other related studies (Wegenast et al 2010, Batistelli et al 2013, Couto et al 2015. Couto et al (2020) used the multinomial model to evaluate haploid induction rate, diploid seed rate and inhibition seed rate.…”

Doubled haploids in maize: Development, deployment, and challenges

“…Results were compared for HIR, diploid seed rate, and inhibition seed rate. Findings showed that HIR, inhibition seed rate, and diploid seed rate were 1.23, 23.48, and 75.21% for F 1 generation and 1.78, 15.82, and 82.38% for F 2 generation respectively (Couto et al., 2019). Conclusively stating that very high inhibition rate was observed in genetic background of tropical germplasm for expression of R1‐navajo phenotype.…”

Haploid maize seeds prediction using deep learning and using mock reference genomes for genomic prediction of hybrids

“…To obtain seeds from induction crosses marked by R1-nj, we used a haploid inducer population derived from a cross of two inducer lines (W23 and Stock6) with a maize hybrid adapted to tropical conditions. This inducer population has a dominant inheritance for the R1-nj marker and a putative haploid induction rate equal to 1.51% (Couto et al, 2019). As donors, we used two commercial singlecrosses, one from the flint and another from the dent heterotic group, where 50 unique plants from the haploid inducer were crossed with two plants from each donor.…”