Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/14/2009
Publication Date: 11/1/2009
Publication URL: handle.nal.usda.gov/10113/37353
Citation: Brooks, S.A., Anders, M.A., Yeater, K.M. 2009. Effect of cultural management practices on the severity of false smut and kernel smut of rice. Plant Disease. 93:1202-1208. Interpretive Summary: False smut (Ustilaginoidea virens) and kernel smut (Neovossia horrida) are largely understudied diseases of rice (Oryza sativa) in the United States. Few assessments of disease resistance and G x E interactions have been performed, and the available information has been principally inferred from incidental experiments. Both diseases are significant and a need exists for their management, but since they are notoriously difficult to work with progress has been limited. In 2006 we began to evaluate the effects of crop management on rice smuts in order to determine G x E interactions, resistance in modern-relevant cultivars, and the optimal conditions to design dedicated smut nurseries. Using a long-term crop rotation experiment that has a history of natural smut infestation we determined the effects crop rotation, tillage and fertility on disease incidence. This study provided the means to harvest large amounts of smutted grain for inoculating two new nurseries that were designed using management strategies which would maximize disease incidence. Here we report the results of the 2006 and 2007 rotation study as well as the 2007 nursery data. We have identified management strategies to minimize smut incidence on susceptible cultivars and have discovered a source of resistance to kernel smut.
Technical Abstract: False smut and kernel smut are diseases of rice that reduce both grain yield and quality. False smut is an emerging disease worldwide that is rapidly gaining in importance, whereas kernel smut has historically been a chronic minor disease with sporadic outbreaks that cause considerable losses. Since both diseases are manifested as damaged rice grain they can be rated concurrently, but no source of resistance has been identified or deployed to control either disease on a production scale. This lack of progress toward improving variety resistance is primarily attributed to the inherent variability and difficulty in obtaining accurate disease ratings. This has resulted in the widespread release of smut susceptible rice varieties, and a need to manage these diseases on current varieties until useful sources of resistance can be identified. Herein we report an integrated approach that achieved disease control through cultural management and identification of resistant germplasm. By employing conservation tillage, continuous rice cropping, and moderating nitrogen fertility rates, we were able to achieve effective field resistance that nearly eliminated false smut from rice varieties which were fully susceptible under conventional cultivation practices. Furthermore, using a disease nursery designed to promote smut severity, two rice hybrids were identified that possessed kernel smut resistance under the most favorable disease conditions.