student profile: Mr Mahbub Rahman


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Thesis work

Thesis title: Development of crown rot resistant and tolerant wheat genotypes using marker assisted recurrent selection

Supervisors: Richard TRETHOWAN , Philip DAVIES , Urmil BANSAL

Thesis abstract:

Wheat (Triticum aestivum L.) is one of the most important food crops around the globe and is one of the most traded agricultural commodities providing over 50% of the world’s food. It’s being a perennial crop, has prone to a wide range of biotic and abiotic stresses which has stressed the need to breed the tolerant and/or resistant crop for these stresses. Among the diseases, Crown rot of wheat and barley is a serious disease caused by the fungus Fusarium pseudograminearum, a stubble-borne pathogen common in no-till farming systems in semi-arid grain growing regions. The disease infected plants display characteristic honey-brown discoloration on the crown and lower stem. Premature ripening of developing heads caused by disruption of vascular tissue results in whiteheads under post anthesis drought conditions, directly leading to grain yield loss. The genetic control of crown rot resistance and tolerance are generally complex, with many minor genes and QTLs are involved in controlling resistance or tolerance in wheat plants. Attempts to combine these polygenes and QTLs using traditional breeding strategies have generally proven ineffective, and therefore novel breeding strategies are required to more efficiently transfer crown rot resistance and tolerance into adapted backgrounds. Therefore, in this study, it was proposed that a novel breeding strategy- Marker Assisted Recurrent Selection (MARS) would be effective in pyramiding the many minor genes controlling the crown rot response. Three MARS populations were developed using multiple sources of resistance and tolerance. Field experiments were conducted at the IA Watson Grain Research Centre at Narrabri and the hybridization and; Doubled Haploid (DH) production work was undertaken at PBI, Cobbitty, The University of Sydney with the following objectives: (i) Establishment of the degree of resistance in MARS populations and assess the reliability of pot based testing for resistance to crown rot (ii) Confirmation of the relationship, if any, between resistance and tolerance (iii) Identification of QTLs that explain crown rot resistance and tolerance and establishment the genetic relationship if any between resistance and tolerance and (iv) Confirmation of response to selection by evaluating parents, the base population, and recombined materials under crown rot pressure.
A total of 475 (250 F2 derived F4’s and 225 selected F5’s were derived from the first population, 225 F4s and 200 F5s were derived from the second population) genotypes were evaluated in pot and field conditions to asses stem disease severity in adult plants. This study indicated that transgressive segregation existed for crown rot resistance in both populations. Disease severity in the pot tests (both summer and winter) was too severe and inconsistent, and hence field screening was considered more reliable and representative of actual genotype responses to crown rot. (Chapter 4).
These 475 lines of both the populations were genotyped using 9K SNP platform. The genotyping and phenotyping data generated in these populations was used in genome-wide association mapping. Subsequently, the plants accumulating high number (18-22 marker combined) of significant markers were used to produce DHs, using the wheat-maize system. A total of 297 double haploids derived lines were phenotyped for crown rot resistance and tolerance and compared against both the recombinant parents and parents of the base population in 2016 and 2017 crop seasons under crown rot pressure. Some of these DH lines showed significantly higher resistance compared to their parents and local cultivars along with well-maintaining grain yield (Chapter 7).
Yield loss trial of 196 lines of population 3 was established under inoculated and non-inoculated plots in 2014 and 2015 to phenotype for both crown rot resistance and tolerance. Some of these genotypes were consistent in their response to crown rot infection across years and these can be successfully used as parents to develop new resistant and tolerant cultivars. A week relationship was observed between yield loss measured as tolerance and basal stem browning measured as resistance (Chapter 5). This population 3 was genotyped using a high-density 90K SNP genotyping array and a genome wide association analysis (GWAS) was done to identify regions controlling the crown rot response in a breeding population combining multiple sources of crown rot resistance and tolerance based on the multi-year, multi-environment data (Chapter 5). A total of 38 QTLs/ genomic regions were associated with resistance and tolerance traits and previously reported 9 QTLs were confirmed through this study. The resistance associated with white head and tolerance was located only on chromosome 2B but the resistance associated with basal stem browning was always independent of tolerance (Chapter 6). These results are now being used to combine multiple trait alleles into a single genotype using MARS, whereby markers are used to combine complimentary pairs of sister lines, in order to pyramid unique alleles.
The outcomes from this study should be worthwhile to the wheat industries in Australia, since breading lines with improved resistance and tolerance, along with the marker information, will be provided to breeding companies to produce new varieties with improved performance under crown rot. Further, this study could document the use of MARS as a breeding strategy for traits with complex, polygenic inheritance in a self-pollinated crop such as wheat.

Selected publications

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Journals

  • Rahman, M., Mandal, M., Alam, M., Rahman, S., Begum, N., Khalil, I. (2017). Identification of drought tolerant spring wheat genotypes based on some of the physiological traits. SABRAO Journal of Breeding and Genetics, 49(1), 104-115.

2017

  • Rahman, M., Mandal, M., Alam, M., Rahman, S., Begum, N., Khalil, I. (2017). Identification of drought tolerant spring wheat genotypes based on some of the physiological traits. SABRAO Journal of Breeding and Genetics, 49(1), 104-115.

Note: This profile is for a student at the University of Sydney. Views presented here are not necessarily those of the University.