Interested Members of the University Community are invited to attend the Final Oral Examination for the Degree of Doctor of Philosophy of Kamal Khadka of the Department of Plant Agriculture
Date: Wednesday, May 6, 2020
Time: 1 pm
via ZOOM Conferencing
Please contact firstname.lastname@example.org if you wish to be added to the list to attend the examination portion of the exam.
Thesis Title: Genotypic and Phenotypic Analysis of a Nepali Spring Wheat (Triticum aestivum L.) Population
Advisory Committee Examination Committee
Dr. Manish Raizada, Advisor* Dr. Gopi Paliyath, Chair
Dr. Hugh Earl Dr. P. Stephen Baenziger, External examiner
Dr. Zeny Feng Dr. Manish Raizada
Dr. Andrew Burt Dr. Andrew Burt
*Dr. Ali Navabi (2015-2019) Dr. Istvan Rajcan
Nepal has been completely dependent on introduced wheat (Triticum aestivum L.) germplasm for variety development despite having >500 landraces in the national genebank. No Nepali wheat genetic resources were involved in the development of any of the 43 varieties released in Nepal for commercial cultivation. Nepal’s capacity to genotype and phenotype its wheat germplasm, in order to utilize it for breeding, is in its infancy due to a lack of resources. To assist breeding efforts for Nepal, here, I hypothesized that: (1) Nepali spring wheat germplasm is genetically and phenotypically diverse; (2) that the important physio-morphological traits have a genetic basis; and (3) that promising accessions for future targeted breeding can be identified using such genotyping and phenotyping. I assembled the Nepali Wheat Diversity Panel (NWDP) consisting of 318 spring wheat accessions including landraces, CIMMYT lines and released varieties. The NWDP was phenotyped in four different field experiments (2 each in Nepal and Canada) and also under controlled conditions. Analysis of 95K high density GBS markers showed greater genetic diversity in the Nepali landrace group compared to modern germplasm. Unexpectedly, the population structure analysis revealed four, rather than 3 subpopulations as was originally expected based on breeding history, with significant admixture within each subpopulation. A genome-wide association study (GWAS) revealed 15 significant marker-trait associations (MTAs) for 6 agro-morphological traits. Targeted genotyping was conducted to assess the accessions for allelic variation at dwarfing loci (Rht) and a photoperiod insensitivity locus (Ppd), both targets of modern selection. Promising accessions for future breeding were identified that possessed dwarfing alleles but conversely also seedling vigour related traits with potential to promote early season drought tolerance. The NWDP also showed significant variation for NDVI, SPAD values and shoot waxiness. I suggest that the Nepali landraces should be further characterized to identify the “authentic” landraces while the genotypic information available should be further utilized in genomic selection. The data suggest that shoot waxiness may be confounding spectral reflectance measurements especially when a germplasm population is extremely diverse. In conclusion, it is hoped that this thesis will better inform and accelerate wheat breeding for Nepal.