Validation of Multiple Disease Resistance QTL from Chromosome Segment Substitution Population in F2:3 Populations

• Main Author: Bastos Martins Marino, Lais
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Horticulture; Plant sciences
• ISBN: 165841697X; 9781658416979

Maize is a staple food in many countries. When not used directly in human consumption, is an essential component of animals’ feed. Diseases are an important factor that can reduce yield or make crops not suitable for human or animal consumption, so managing them is a key aspect of modern agriculture. One way that presents less environmental risk and lower cost for the farmer is through genetic mechanisms for disease resistance. The first chapter of this thesis is a literature review that gives an overview of disease resistance, multiple disease resistance (MDR) concepts and explains quantitative trait loci (QTL) mapping tools. The chapter also characterizes the three foliar diseases of maize (Zea mays L. ssp. mays): southern leaf blight (SLB), northern leaf blight (NLB) and gray leaf spot (GLS).The second chapter consists of a study that performed an independent test using a F2:3 population of the putative MDR QTL previously found in a chromosome segment substitution line (CSSL) population. The goal was to have more precise estimates of allele additive effects and study dominance effects. Twelve F2:3 populations were made from crosses between the CSSL that showed strongest resistance across the three diseases and their recurrent parent, maize line H100. The resulting populations were assessed for each of the three diseases in replicated trials and genotyped with the markers previously associated with disease resistance. The effects of 16 QTL out of 44 were validated; the study provides further evidence for the existence of MDR QTL and demonstrates the importance of independently evaluating QTL effects following their initial identification.In the third chapter, a preliminary experiment was done to evaluate spore adhesion of the SLB pathogen Cochliobolus heterostrophus to different maize lines, as it could potentially be a mechanism of disease resistance. A novel spore adhesion protocol was developed, and a timeline of spore attachment was made using leaf samples from the maize lines B73 and Mo17. We evaluated the number of spores attached on a leaf sample of the lines Mo17, B73, P39, HP301, NC350 and Ki3. Although the number of spores attached to the leaf did not perfectly correlate with field disease resistance, we believe that in some cases maize host genetics affects spore adhesion to the leaf.