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Variation in the reaction of hard red winter wheat cultivars to common root rot and spot blotch
N. GRAF GRACHET (1), R. M. Hunger (1), M. E. Payton (1), J. Edwards (1). (1) Oklahoma State Univ, Stillwater, OK, U.S.A.

The incidence of residue-borne wheat diseases has increased in Oklahoma due to adoption of no-till cultivation. This includes common root rot (CRR) and the foliar disease spot botch (SB), both caused by <i>Bipolaris sorokiniana</i>. Screening for reaction to CRR and SB currently is not conducted, so the goal was to determine if useful levels of resistance to these diseases exist in hard red winter wheat (HRWW) cultivars. For SB, seedling foliage of 14 cultivars was sprayed with a spore solution (105 and 106 spores/mL). Disease was visually assessed by rating percent infected leaf area and by using Assess quantification software (Lamari, 2008, APS Press). For CRR, seeds of 3 cultivars were inoculated with a spore solution (105 and 106 spores/mL) and incubated at 25°C in the dark between wet filter paper. Root system reduction (area and length) was determined using Assess. For SB, a high correlation (R2 = 0.91) was observed between visual rating and Assess. Average severity was 30% across all cultivars; Billings, Ruby Lee and Garrison showed the best resistance (12%). For CRR, root length and root area were highly correlated (average R2 = 0.86), but root length provided greater differentiation between varieties. Percent root length reductions were 12, 22, and 41 for Duster, Endurance, and Iba, respectively. These results indicate useful levels of resistance to SB and CRR may be available in HRWW varieties.

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