Fitness Evaluation of Rcg1 , a Locus that Confers Resistance to Colletotrichum graminicola (Ces.) G.W. Wils. Using Near-Isogenic Maize Hybrids

Anthracnose caused by Colletotrichum graminicola (Ces.) G.W. Wils. is an important stalk rot disease in maize (Zea mays L.). The impact of genetic resistance to plant pathogens is extremely important from both economic and environmental standpoints. The objectives of this study were to determine if any fitness costs were associated with the Rcg1 locus that confers resistance to C. graminicola in maize and to determine the effect of Rcg1 on grain yield in the presence of disease. Near-isogenic hybrids (NIHs), created by crossing B73Ht and Mo17Ht with near-isogenic lines (NILs) DE811 and DE811ASR(BC 5 ), were evaluated under three treatment regimes: inoculation with C. graminicola, inoculation with water (wounding), and no inoculation. The experiment was conducted in a replicated split-split-plot design at six locations. Results indicate that the NIL DE811ASR(BC 5 ) does not cause significant negative effects in hybrid combinations for most agronomic traits compared to hybrids made with the recurrent parent, DE811, and that there was no apparent fitness cost associated with Rcg1 in uninoculated or wounded treatments. The presence of Rcg1 reduced the overall yield impact incurred by infection in inoculated plots by almost three fold in comparison to the NIHs that lack the gene. These results, in addition to the asexual life cycle and limited variability of C. graminicola, imply that Rcg1 may be a durable resistance locus.