QTL Analysis for Identification of BPMV Resistance Genes in Soybean.

Bean pod mottle virus (BPMV) has become widespread in major soybean production areas in the USA.  There is no documented resistance to BPMV, and yield losses of 3% to 52% have been reported.  The objective of this project was to identify putative quantitative trait loci (QTL) associated with BPMV resistance.  Based on observations over years and locations in Nebraska, two soybean genotypes with the lowest average foliar symptoms and seed mottling scores were selected as resistant parents, and the cultivar IA3010 was selected as the common susceptible parent.  Two populations of 254 F4:5 lines each were developed.  Field experiments were conducted during 2005 to 2007 at the University of Nebraska-Lincoln.  Each plot was mechanically inoculated with BPMV isolate subgroup I originally collected in Nebraska.  All lines tested positive for BPMV, indicating no complete resistance.  Consequently, a quantitative ELISA protocol was developed to assess relative viral antigen (RVA) as a measure of plant response to BPMV infection.  Percent mottled seed also was determined.  Genotypes for the 19% of lines in each tail with the most extreme phenotype for a trait were determined using SSR and SNP molecular markers across all 20 soybean linkage groups.  QTL mapping employed Map Manager QTXb20 with a user-defined map distance approach.  One QTL was associated with mottled seed in both populations, and was located near the T locus on linkage group C2, with a LOD score of 4.0.  Three putative QTL associated with lower viral titer on leaf tissue were identified in the population that was measured for RVA.  The LOD scores were low, ranging from 1.1 to 1.4, with each QTL accounting for approximately 6% of the total phenotypic variance for RVA.  Further study of the putative QTL for RVA is of interest to investigate possible mechanisms of limiting virus replication in the plant.