Botany and Plant Pathology Seminar Series
Speaker: Ms. M. Patricia Romero - Department of Botany and Plant Pathology - Purdue University
Topic: Inheritance and mapping of genes associated with Diplodia ear rot resistance in maize
When: Wednesday, October 31, 2012 at 3:30 pm in WSLR 116

Diplodia ear rot caused by Stenocarpella maydis is considered the most common ear rot pathogen in hybrid corn, and seed quality is compromised in infected ears. The absence of durable commercial resistance makes it necessary to explore alternative options for management. The objectives of this study are i) determine the efficacy of fungicide applications for Diplodia ear rot, and  ii) identify and map resistance to Diplodia ear rot by screening a population of recombinant inbred lines (RIL). Field experiments were conducted during 2011 and 2012 in two locations in Indiana to determine efficacy of the fungicides Quilt Xcel® (azoxystrobin + propiconazole; Syngenta Crop Protection) and Proline® (prothioconazole; Bayer Crop Science). The experiment was designed as a split-plot with inoculation treatment as the whole plot, and fungicide application timing as the subplot. Plants receiving an inoculation treatment were inoculated by placing S. maydis colonized sorghum in the whorl during vegetative growth stage (V7). Fungicide treatments consisted of an application of the label rate of fungicide at an early vegetative growth stage (V6), tasseling/silking (R1), or milk stage (R3). In both years, fungicide treatment did not significantly reduce disease severity at any application timing compared to the untreated control in non-inoculated or inoculated plots.  Resistance to S. maydis is quantitatively inherited and highly influenced by environment. A study was conducted near Lafayette, Indiana to locate potential quantitative trait loci (QTLs) and molecular markers involved in resistance to Diplodia ear rot in the corn intermediate B73 x Mo17 (IBM) population of recombinant inbred lines (RIL). The 302 lines were planted with one replication in 2010, and two replications in 2011 and 2012. Each line was artificially inoculated at a vegetative growth stage (V7) with sterilized sorghum seed colonized with S. maydis.  A set of 1339 Simple Sequence Repeats (SSR) or microsatellite, and Single Nucleotide Polymorphisms (SNPs) markers on the 302 lines were analyzed by composite interval mapping (CIM) with Windows QTL Cartographer version 2.5. Data collected from 2010, 2011, and 2012 were analyzed using a threshold LOD of 2.5 cM. One single QTL was detected each year in 2010 and 2011. In 2012 no significant QTL was detected due to adverse environment conditions and small population size. Enhancements in progeny type and population size need to be considered before establishing further QTL mapping studies in Diplodia ear rot.


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