Crop improvement is dependent upon genetic diversity. The rate of genetic gain in breeding programs can increase by extending the amount or nature of variation available for selection using land races and wild relatives. However, exotic germplasm carries a range of undesirable traits, such as grain shattering, tall plant type, lodging, low yield potential, that limit their suitability for modern agriculture. Back-crossing to locally adapted varieties and pre-selection for traits is therefore required to ensure that meaningful data can be generated in field trials.
Multiparental schemes such as Nested association mapping (NAM) populations enabled to use exotic germplasm as a resource for the discovery of novel traits and QTL/genes. NAM combine the power of linkage analysis and the precision of association mapping. In NAM population development, founder lines are crossed with the same reference line to develop sets of related mapping progeny. When jointly analysed, NAM populations can provide higher power to detect QTL than in any of the constituent biparental families separately. NAM also have the advantages of association mapping of high diversity and resolution. Many historical recombination events between founders provides fine resolution as in association mapping allowing high resolution to localise QTL.
The program aim to develop a large NAM population using two Australian modern wheat varieties as reference parents and a diverse set of donor lines. Some of the donor lines are known for their tolerance to drought and heat, and nitrogen use efficiency.
Backcrossing and early plant culling will enable to avoid undesirable traits and generate populations amenable to modern agronomical practices.
NAM populations are being generated using 75 wheat accessions from the diversity panel from different continents and two Australian varieties, Gladius and Scout, as recurrent parents. Altogether the NAM population will be composed of 100-150 subpopulations, each of 100-200 lines to give a total population of over 10,000 lines.
The NAM population will be genotyped using high-throughput marker technology for genetic mapping. The genetic variation between parental lines is being evaluated for tolerance to drought and heat and for grain protein content. The most variable NAM families will be phenotyped under field conditions to identify QTL for yield and grain protein content in Australian environment.
Melissa Garcia (program 2 leader)
Langridge P and Fleury D (2011) Making the most of “omics” for crop breeding. Trends in Biotechnology 29: 33.