Mapping for QTLs related to Nitrogen Use Efficiency in Hexaploid Wheat under Australian Conditions

Masood Anwar

Nitrogen (N) is one of the main limiting factors to wheat production and yield. Since the Green Revolution, there has been an increasing trend in N fertiliser application to maximise wheat output. This also increases the risk of N losses due to leaching and volatilisation, which has been estimated as 50-70% of the applied N. Plants' ability to convert applied N to the yield is termed Nitrogen Use Efficiency (NUE). Until now, NUE has not been directly targeted in the wheat breeding programs. Still, in the past few years, NUE for the latest wheat varieties increased mainly because of breeding for high yield and higher grain protein contents under limiting N conditions. Recently, efforts have been made to include NUE in breeding programs but are limited by the very little understanding of the genetic factors involved in the NUE mechanism. The present study attempts to understand the genetics of NUE in field conditions and the effects of N on plant root morphology to optimise N uptake by the plants. To detect the genetic loci responsible for NUE and yield-related traits, two wheat double haploid (DH) populations, Spitfire/Mace of 172 individual genotypes and Suntop/3BL (Bethlehem-Chromosome arm substitution line 3BL) of 164 individual genotypes, were used for phenotyping and mapping. These populations were planted at three locations, Muresk and Williams in Western Australia and Narrabri in New South Wales, with varying levels of N at each site. The genetic maps were constructed for both populations using 2235 SNP markers for Spitfire/Mace and 1925 SNP markers for Suntop/3BL populations. Forty-nine loci with 70 QTLs were detected in Spitfire/Mace population, and 26 loci with 45 QTLs were observed in Suntop/3BL population. From these QTLs, six significant QTLs related to NUE and yield-related traits were observed, which can further be studied and utilised in breeding programs. A root morphology study in relation to basal Nitrogen dose with Spitfire/Mace population revealed a significant influence of N application on Root System Architecture (RSA) traits. Twenty-six loci with 45 QTLs were observed on 11 chromosomes. Two major pleiotropic groups on chromosome 1A and chromosome 7A were further explored to obtain candidate genes related to RSA traits. Seven candidate genes were identified in these regions that are putatively associated with RSA traits. Furthermore, three genes: Cyclophilin-71, Crinkyl-4 kinase-like protein and Auxin responsive protein PAP1, were found to be directly responsible for rooting morphology in the model plant Arabidopsis. The gene expression profiles of these lines in selected long root and short root genotypes also confirmed the involvement of these genes in the RSA trait. These results provide new genetic information and resources for the NUE-related traits that can be utilised in the wheat breeding programmes to improve wheat NUE. The additional confirmation of identified candidate genes related to the RSA traits can provide initial steps toward using root traits to improve yield and NUE.

Mapping for QTLs related to Nitrogen Use Efficiency in Hexaploid Wheat under Australian Conditions

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