Genetic Vulnerability and the Relationship of Commercial Germplasms of Maize in Brazil with the Nested Association Mapping Parents

Abstract

A few breeding companies dominate the maize (Zea mays L.) hybrid market in Brazil: Monsanto® (35%), DuPont Pioneer® (30%), Dow Agrosciences® (15%), Syngenta® (10%) and Helix Sementes (4%). Therefore, it is important to monitor the genetic diversity in commercial germplasms as breeding practices, registration and marketing of new cultivars can lead to a significant reduction of the genetic diversity. Reduced genetic variation may lead to crop vulnerabilities, food insecurity and limited genetic gains following selection. The aim of this study was to evaluate the genetic vulnerability risk by examining the relationship between the commercial Brazilian maize germplasms and the Nested Association Mapping (NAM) Parents. For this purpose, we used the commercial hybrids with the largest market share in Brazil and the NAM parents. The hybrids were genotyped for 768 single nucleotide polymorphisms (SNPs), using the Illumina Goldengate® platform. The NAM parent genomic data, comprising 1,536 SNPs for each line, were obtained from the Panzea data bank. The population structure, genetic diversity and the correlation between allele frequencies were analyzed. Based on the estimated effective population size and genetic variability, it was found that there is a low risk of genetic vulnerability in the commercial Brazilian maize germplasms. However, the genetic diversity is lower than those found in the NAM parents. Furthermore, the Brazilian germplasms presented no close relations with most NAM parents, except B73. This indicates that B73, or its heterotic group (Iowa Stiff Stalk Synthetic), contributed to the development of the commercial Brazilian germplasms.

Genomic analysis of maize lines introduced in the early stages of a breeding programme

“…This result agrees with that of Andrade et al. () and might indicate that the B73‐SSS lines are normally used as a recurrent parental in the tropical germplasm.…”

“…In our study, which used a broader background and more marker coverage, the B73-derived lines presented a low relationship with tropical lines. This result agrees with that of Andrade et al (2016) and might indicate that the B73-SSS lines are normally used as a recurrent parental in the tropical germplasm.…”

“…Andrade et al. () reported that Brazilian commercial hybrids present a low similarity with SSS‐NAN lines but not with the B73 line. In our study, which used a broader background and more marker coverage, the B73‐derived lines presented a low relationship with tropical lines.…”

“…The OLS-GWS model refers to the regression using only the four significant markers obtained by the BSSV method collection, the crossings between heterotic groups SSS 9 NSSS; SSS 9 Lancaster; NSSS 9 Lancaster and M-Arg 9 F-Arg would be preferable to crossings F-Arg 9 Lancaster, Iodent 9 NSSS and Iodent 9 M-Arg as they show a higher distance among themselves. Andrade et al (2016) reported that Brazilian commercial hybrids present a low similarity with SSS-NAN lines but not with the B73 line. In our study, which used a broader background and more marker coverage, the B73-derived lines presented a low relationship with tropical lines.…”

Population structure analysis and identification of genomic regions under selection associated with low-nitrogen tolerance in tropical maize lines

“…Previous studies showed that maize gene pools present a clear population structure between temperate and tropical/subtropical pools. While the tropical maize germplasm has greater genetic diversity, the temperate germplasm presents more pronounced heterotic patterns [ 11 – 14 ]. However, the tropical maize germplasm lacks information on the genetic relationship [ 14 ] and genetic variation under low-N stress [ 8 ].…”