Wheat Ear Sterility Project (WESP)

ABSTRACT

This is the final report of a 42-month project (RD-2007-3438) which started in September 2009. The total cost of the work was £350,953, which was funded by Defra and BBSRC (Control of infertility in wheat by phenotype screening and genetic analysis of varieties and breeding lines, SA LINK LK09116) and including a contract for £70,832 from AHDB Cereals & Oilseeds.

The overall aim of this project was to establish methods for phenotypic screening and crop data collection to support QTL mapping of variation in wheat ear sterility. This is the precursor to understanding the genetics underlying vulnerability to sterility in UK wheat, with a view to identifying DNA markers for its elimination from breeding programmes. Our approach was to undertake population phenotyping coupled with genotyping and candidate plant trait identification and validation. The key drivers to the work were threefold:

• To protect UK wheat crops against potentially devastating crop losses
• To  establish the occurrence of major and subclinical effects of sterility on yield potential
• To support a strategy to improving breeding efficiency by elimination of vulnerable material in early generation selection and enable breeders to have more confidence in the deployment of diverse breeding materials

Partnering plant breeding companies supplemented an existing doubled-haploid (DH) population, Avalon x Cadenza, with four bi-parental DH populations coded as 9M, FA, LQ and TR, with approximately 100 lines in each. Populations were grown at an AHDB/BSPB RL/NL wheat site in East Lothian, Scotland. A weather station was located adjacent to the wheat plots. Previous reports of moderate to high levels of ear sterility in winter wheat variety trials at this site had been reported to to AHDB. Populations 9M, LQ and TR were grown in 2008-09, whilst all five populations were grown in 2009-10, 2010-11 and 2011-12. Over the four harvest years, a total of thirteen population x year combinations were assessed for ear sterility in the field and laboratory.  

Quantitative assessments for assessing ear sterility were developed for in-field assessment of the condition, whilst lab assessments, on ears sampled prior to harvest, were based on scoring of all florets along one side of each ear (detailed assessment) or outer florets only (rapid assessment). Evidence for particular sensitivity of outer floret sterility in vulnerable varieties has been established, with differentiation between sub-clinical and yield limiting levels of sterility. For genotyping and map construction, the Avalon x Cadenza cross is a UK reference population with a map publically available. New genotyping was done initially using diversity arrays technology (DArT) on population M9. Subsequently, moderate to good segregation for sterility across populations (M9, FA, LQ and TR) allowed us to take advantage of new SNP genotyping technology using the KASP marker system.

Following genotyping and linkage mapping of all populations, QTL analysis has indicated flowering time and growth stage QTL on several chromosomes. These previously reported QTL serve as good controls for dataset integrity. More importantly, these analyses have indicated an accumulation of several weak ear sterility related QTL on specific chromosomes. None of these QTL were common across the five populations, though there was evidence for a cluster of QTL on chromosome 7A (with three QTL). This provides evidence for a difference in the genetic control of ear sterility between varieties and populations. Environmental interactions with the level of phenotypic expression were complex. Monitoring of several weather variables indicated that reduced radiation level and air temperature increased crop susceptibility to sterility during the booting growth stage (GS41-45).