Position: PhD student
Place of birth: France, Nantes
Languages: English, French, Spanish
Scholarships: Grains Research and Development Corporation
Dr Mandy Christopher
Water availability is a major limiting factor for wheat production in rain-fed agricultural systems worldwide. Crops ability to explore the soil profile and extract available water at different depths is largely determined by root architecture. For instance in wheat, narrower lateral root distribution and a higher proportion of roots at depth can provide access to deep soil moisture late in the season and potentially improve yield and yield stability under terminal moisture stress. Such favourable root traits have been associated with narrower seminal root angle and high root number in wheat seedlings. Selection for desirable root architecture in breeding programs could assist the development of high-yielding drought-tolerant wheat cultivars.
My PhD project seeks to develop new tools to enable wheat breeders to target specific root traits, including
- A high-throughput and cost-effective phenotyping method for seedling root angle and root number
- Characterisation of genotypic diversity and genetic controls of root traits
- DNA markers associated with target quantitative trait loci (QTL) for root traits in multiple genetic backgrounds
The first step of my PhD project was to develop a low-cost high-throughput phenotyping method to facilitate selection for desirable root traits. We developed a method to assess ‘seminal root angle’ and ‘seminal root number’ in seedlings – two proxy traits associated to root architecture of mature wheat plants. The method involves measuring the angle between the first pair of seminal roots and the number of roots of wheat seedlings grown in transparent pots. Images captured at 5 to 10 days after sowing are analysed to calculate root traits. This approach has been shown to be highly reproducible, it requires little resource (time, space, and labour) and can be used to rapidly enrich breeding populations with desirable alleles for narrow root angle and a high number of seminal roots to indirectly target the selection of deeper root system with higher branching at depth.
The new phenotyping method will be used to screen segregating populations for root angle at the BC1F2, BC1F3 and BC1F4 stages. Consecutive cycles of bi-directional selection will be employed to develop “tail” populations representing extreme phenotypes for “narrow” and “wide” root angle. These tail populations will be genotyped using the DArTseq DNA marker platform. Marker frequency analysis comparing the tail populations and association mapping will be used to identify genomic regions influencing trait expression.
In parallel, a nested-association mapping (NAM) strategy will be applied to dissect the genetic control of root traits. A large NAM population comprising 900 F4-derived recombinant inbred lines (RILs) has been developed. Populations developed by crosses to a number of donor sources for root traits have been nested within three adapted Australian wheat cultivars to provide genetic variation and estimate effects related to genetic background. The NAM population have been genotyped with DArTseq markers and characterised for root angle and root number using the newly developed screening method. Field data collected for the NAM population in the 2014 and 2015 seasons will be used to investigate the putative effect of root traits on expression of stay-green and yield. QTL for root traits identified in the NAM population will be positioned on a consensus map and aligned with those identified in the tail populations.
In the media
Can clear pots build drought-proof wheat?
Wheat could be drought proof
Richard CA, Hickey LT, Fletcher S, Jennings R, Chenu K, Christopher JJ (2015) High-throughput phenotyping of seminal root traits in wheat. Plant Methods DOI 10.1186/s13007-015-0055-9