Managing Global Resources for a Secure Future

Sorghum is a multipurpose drought-tolerant C4 plant, grown for food, feed, fiber and fuel. The Sugarcane aphid (SCA), Melanaphis sacchari (Zehntner) is currently one of the most important insect pests of grain and forage sorghum in the Southern US. SCA can cause significant damage to plant and severe yield loss in sorghum. Host plant resistance to SCA is a sound method for the control of this damaging pest. Mapping genes for resistance to SCA is an important aspect of understanding the molecular basis of host plant defense in sorghum. The objective of this study is to analyze the genetic control of resistance to SCA and locate resistance loci into specific genomic regions of sorghum. A mapping population was developed by crossing an elite line, F_2:3 families BTx623 (susceptible parent) with a resistant donor (sugarcane aphid resistant line), Then, I genotyped the resulted F₂ population using those existing SSR markers and additional newly developed markers in order to cover all ten chromosomes of sorghum and to narrow-down the marker interval carrying resistance locus. Simultaneously, I evaluated all F_2:3 progenies by screening those seedlings against virulent SCA in growth chambers. With the collected two sets of data from genotyping and phenotyping experiments, linkage analysis was performed using the mapping software Map-Maker 3.0. For QTL analysis, composite interval mapping (CIM) and multiple interval mapping (MIM) were performed using Windows QTL Cartographer 2.5. In this way, it is anticipated that linkage relationship between SSR markers used in genotyping and SCA resistance loci was established and resistance QTLs was mapped into specific locations of the chromosomes of sorghum. Finally, SSR markers closely-linked to the resistance QTLs and identification of chromosomal regions responsible for sugarcane aphids will facilitate both map-based cloning and marker-assisted breeding of new hybrids or cultivars with genetic resistance to sugarcane aphids.