Assessment of Spring Wheat Genotypes for Disease Reaction to Rhizoctonia solani AG‐8 in Controlled Environment and Direct‐Seeded Field Evaluations

Abstract

into undisturbed soil (Anonymous, 2001). Over 263 000 ha of cropland devoted to small grain production is now Rhizoctonia root rot, caused by Rhizoctonia solani Kuhn AG-8 under direct seed management in the PNW, of which (Anastomosis Group 8), is a yield limiting disease of direct-seeded cereal grains. The objectives of this study were to (i) determine 50% is planted to spring cereal grains (Pacific North- whether spring wheat (Triticum aestivum L.) genotypes vary in sus- west Direct Seed Association, 2001). Spring crops are ceptibility to Rhizoctonia root rot in inoculated field trials; and (ii) valuable in direct-seed systems due to the retention of evaluate whether disease ratings obtained by controlled environment undisturbed crop residue during the winter, when most (CE) analyses are predictive of disease ratings or genotype perfor- precipitation occurs in the PNW. Direct-seeding also mance in the field. Twenty-one spring wheat genotypes were evaluated maximizes soil water retention and increases water infil- for two crop years in a split-plot field study with high and low levels tration, which diminishes the risk of soil erosion while of disease pressure. The high-inoculum (high) treatment consisted of increasing crop productivity (Papendick, 1998). plots planted the previous fall with a 3:1 mixture of winter wheat and Attempts at grain production via direct-seeding in the oat (Avena sativa L.) grains colonized by the pathogen. The low- 1970s in the PNW failed due to problems associated inoculum (low) treatment was neither inoculated nor planted with a green bridge host the previous fall. Genotypes also were assayed with increased fertilizer requirements, rodent damage, for disease reaction in controlled environment (CE) assays. Average and increased pest and disease pressure (Papendick and disease ratings of field entries in the high treatment were 2.1 times Miller, 1977; Cook, 1991). Although direct-seed systems greater than those from the low treatment (P 0.05). The yield have evolved through the years to minimize these risks, average of entries in the high treatment was 87% of that of entries root diseases have resulted in tremendous yield and in the low treatment (P 0.001). Adult plant heights also were 5 cm crop quality losses when small grains are direct-seeded shorter (P 0.001), heading date was slightly delayed (P 0.05), into standing stubble of barley (Hordeum vulgare L.) and grain protein content decreased slightly (P 0.05) in the high or wheat (Wiese, 1987; Smiley et al., 1989; Cook, 1990, compared with the low treatment. Test weight was not affected by 1991; Cook and Haglund, 1991; Smiley, 1996). inoculum level. A statistically significant, negative association (P Rhizoctonia root rot, caused by the fungus R. solani