Combining Ability of Brown Patch Resistance in Tall Fescue.

Brown patch, caused by the fungus Rhizoctonia solani Kuhn, is one of the most devastating diseases that can occur on tall fescue (Festuca arundinacea Schreb.).  The development of resistant cultivars to brown patch would provide the most effective, long term control to this disease.  The objective of this study was to estimate the general (GCA) and specific (SCA) combining abilities of brown patch resistance in tall fescue.  Reciprocal crosses were made between three resistant and three susceptible genotypes using a diallel design.  Progeny from each reciprocal cross were randomly selected and planted in a field trial in the fall of 2006 along with clonal replicates of each of the parents.  The field trial was arranged in a randomized complete block design with four replicates, each replicate was composed of twenty five progeny from each reciprocal cross.  To ensure uniform disease pressure, the field was inoculated with a single R. solani isolate at a rate of 0.8 g m^-2 of prepared inoculum. Visual disease ratings were taken on a weekly basis when symptoms of the disease appeared using a scale of 1-9, with 9 representing the least amount of disease.  The three resistant parents all had significant, positive GCA effects while the three susceptible parents all had significant, negative GCA effects.  The GCA effects accounted for a larger proportion of the sum squares than the SCA effects, suggesting that additive gene effects are more important than non-additive gene effects in brown patch resistance.