Student Presentations

Charity Chidzanga

Webinar title: Development and Utilization of the Wheat Hub Nested Association Mapping Population

Abstract

Nested Association Mapping (NAM) populations are invaluable resources in plant breeding and genetics as they enable the extension of genetic diversity, increase the power to dissect quantitative traits and provide germplasm for breeding programs. We developed a Wheat NAM population, the Wheat- Hub NAM, by crossing 73 diverse exotic lines to two elite Australian varieties Gladius and Scout, followed by backcrossing the F1 to the recurrent parents and subsequently selfing the BC1F1 to generate BC1F4:6. Backcrossing the F1 to the two recipient parents and culling in the BC1F2 generation reduced the variability in flowering time and plant height. The resultant 3535 BC1F4:6 RILs from 125 families were genotyped using a customised genotyping by sequencing approach that generated multi-allelic haplotype markers. Population structure analysis of our NAM population revealed weak population structure that was attributed to the two recipient parents. Using a subset of the NAM consisting of 530 BC1F4:6 NAM RIL lines from 28 families we assessed the utility of the NAM population in QTL mapping. The NAM subset was grown and evaluated for maturity (Zadok’s score), plant height, yield and thousand grain weight (TGW) across a total of five multi-environment field trials during the 2017 to 2019 Australian growing seasons. RTM-GWAS approach was used to detect QTL. We detected five QTL for Zadok’s score, three QTL for plant height, seven QTL for yield and twelve QTL for TGW. The locus associated with the photoperiod response (Ppd-D1) gene was detected for Zadok’s score in all the trials and was also detected for TGW. The other four loci detected for Zadok’s score were located on chromosomes 2B, 3A and 5A. For plant height, one new loci on chromosome 6A was detected together with the loci associated with the Rht-D1 and the Rht-B1 genes. The Rht-D1 loci was also detected for yield. Of the seven loci detected for yield, two loci on chromosome 3B and 4B had favourable alleles that were contributed by the exotic parents. Five of the twelve loci detected for TGW had favourable alleles that were only found in the exotic parents. These results indicates that the Wheat Hub NAM population is a useful genetic resource for dissection of various qualitative traits and for introgression of favourable alleles from exotic germplasm into elite lines.



Abdeljalil El Habti

Webinar title: Investigating carbohydrate availability, plant water use and oxidative stress as potential indicators of tolerance to combined drought and heat stress

Abstract

Drought and high temperatures commonly occur simultaneously in wheat growing regions and greatly challenge wheat production. Recent research shows that plant response to multiple stresses is unique and cannot be extrapolated from plant response to individual stresses. Little is known about wheat physiology under the combination of drought and heat stress.

In my PhD project, we identified carbohydrate availability, plant water use and oxidative stress as potential indicators of tolerance to combined drought and heat stress. We found that glucose and fructose concentrations in grains measured 12 days after anthesis were associated with total grain weight at harvest. Three-day heat stress differentially affected transpiration response to vapour pressure deficit, immediately reducing daily water use in some genotypes while other genotypes were able to maintain water use.

We found that water flow to the spike, used as a surrogate for transpiration in the spike, was not reduced by drought and heat stress, unlike leaf transpiration, which suggested differential regulation of transpiration under stress depending on the transpiring organ. Visualisation of xylem embolism in wheat plants confirmed that the peduncle was more resistant to embolism than the flag leaf, which could be a protective mechanism of the reproductive organ under stress. Finally, we tested a method to monitor oxidative stress in vivo using optical fibres.



Margaret Kirika

Webinar title: Understanding nitrogen uptake, partitioning and remobilization to improve grain protein content in wheat.

Abstract:

In cereals production, nitrogen (N) fertilizer management is necessary to maximize yield and grain protein content (GPC). Unfortunately, uptake of N fertilizers is low in wheat, necessitating the focus on improving N uptake/utilization and better N fertilizer management. In addition, there is a negative correlation between grain yield (GY) and GPC, with physiological traits correlating to this negative relationship not well understood. My PhD research focused on identifying the effects of foliar N application towards improving GPC. There was a significant increase in Gregory GPC following foliar N application at heading and seven days-post-anthesis (7 DPA). We also identified the leaf surface structures correlated to efficient foliar N uptake in four bread wheat genotypes Spitfire, Gregory, Kukri and RAC875 at stem elongation and 7 DPA. Trichome density, primary alcohols and alkanes were correlated to foliar N uptake at 7 DPA. Furthermore, a maximum foliar N absorption occurred in the first two hours of treatment, while the N form preferentially taken up as foliar was urea when compared to ammonium and nitrate, with the highest accumulation in the grain tissues. The leaf expressed N transporters were either upregulated or downregulated after foliar N treatment. There were negative feedbacks of foliar N application on root N accumulation and gene expressions of root nitrate transporters . Finally, to decipher the negative correlation between GY and GPC, we identified some physiological traits associated with the two important agronomic traits in 15 genotypes from a genetic diversity panel contrasting for GPC. In conclusion, we identified an N management strategy to improve GPC in wheat, as well as key physiological traits correlating to GY and GPC.