Synbreed: Immortal biological resources in maize

Access to immortal biological resources is key for the genetic analysis of complex traits and genetic phenomena such as epistasis, genotype by environment interaction and environmental sensitivity.

In project R1 two biological resources will be created

1. a large library of maize doubled haploid lines derived from different European landraces and
2. a two-segment introgression library segregating for important agronomic traits.

In collaboration with projects T2 and T4 both resources will be subject to extensive genotyping, phenotyping and metabolic profiling. Genome wide and candidate gene association analyses will be performed to assess the allelic diversity in European maize germplasm.

The well defined genetic structure of  the introgression library will be a valuable tool for the analysis of gene-gene and gene-environment interactions. Population genetic analyses in collaboration with project A4 will provide insights into the genetic structure of the maize genome. Both resources will be available for collaborative research beyond the scope of Synbreed.

Project R1

Maize landraces are open pollinated populations selected by farmers over decades and adapted to various environmental conditions. Landraces possess a higher genetic diversity than commercial breeding material and represent therefore a potential source of new alleles for resistance or for tolerance against biotic and abiotic stresses. However, their use in conventional breeding programs is constrained mainly because of the genetic load of wild genes resulting in a prolonged breeding cycle. 

Double haploid (DH) lines are completely homozygous lines usually derived from F1 or F2 population and they are obtained by doubling the single chromosome set of haploid plants by Colchicine-treatment. The haploid seed can be easily identified by selecting for the purple marker color of the endosperm and a white marker color of the embryo.   Once derived, the double haploid lines can be reproduced ab libitum by selfing, resulting in fixed “immortalized” genotypes.

When DH lines are obtained from a heterozygous population such as landraces, only a limited fraction of the haploid seedlings will survive and develop till the adult stage, due to the uncovered genetic load. Thus, with this method the genetic burden is strongly reduced in a relative short time. Deriving a large numbers of DH lines from landraces allow to fix and preserve their complete genetic diversity into so called DH libraries.

In this project we build a comprehensive DH library from 80 maize landraces, and tested it for their testcross performance in several environments. Forty of those landraces were tested for a colorless marker expression of their embryo to ensure optimal visual selection of derived haploid seeds. The suitable landraces were then induced and doubled on large scale to compensate the lost of genetic diversity due to the high genetic load.

The here developed DH library is a tool of formidable importance now available for breeding research, allowing to investigate complex genetic issues and broaden the genetic basis of maize breeding.