The multi-year effects of repeatedly growing cotton with moderate resistance to Meloidogyne incognita

Authors: Davis, Richard; KEMERAIT, ROBERT - University Of Georgia

Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2009
Publication Date: 12/3/2009
Citation: Davis, R.F., Kemerait, R.C. 2009. The multi-year effects of repeatedly growing cotton with moderate resistance to Meloidogyne incognita. Journal of Nematology. 41:140-145.

Interpretive Summary: This study documents the cumulative effect of moderate resistance on root-knot nematode (Meloidogyne incognita) population density, root galling, and yield suppression in the southern United States when a moderately resistant cotton genotype was grown continuously for three years. We first documented that the cotton genotype Phytogen PH98-3196 reduced root-knot nematode reproduction by 77% and Acala NemX reduced reproduction by 85% compared to Delta and Pine Land DP458 B/R, so PH98-3196 and NemX were moderately resistant. Cotton was grown in fumigated and non-fumigated plots to measure yield loss. Each genotype and nematicide combination was planted in the same place for three years at two sites to document cumulative effects. In 2006, following three years of the different genotypes, all plots at one site were planted with susceptible cotton to document residual effects of planting resistant genotypes. Root galling and nematode population densities in the soil were significantly lower, and percentage yield suppression was numerically lower, when moderately resistant cotton was grown compared to the susceptible standard in both fields in all three years. Differences between susceptible and moderately resistant genotypes are established quickly (after only one season) and then either maintained at similar levels or slightly increased in subsequent years depending on initial nematode levels. However, when susceptible cotton was grown following three years of the moderately resistant genotypes, the nematode suppression provided by moderate resistance was undetectable by the end of the first season. Moderately resistant cotton genotypes are more beneficial than previously believed and should be pursued for their significant contribution to nematode management. Rotation of moderately resistant cotton and susceptible cotton could be used along with nematicides to manage root-knot nematodes in a continuous cotton cropping system and reduce selection pressure on the nematodes.

Technical Abstract: This study documents the cumulative effect of moderate resistance on Meloidogyne incognita population density, root galling, and yield suppression in the southern United States when a moderately resistant cotton genotype was grown continuously for three years. Cotton genotypes were Phytogen PH98-3196 (77% suppression), Acala NemX (85% suppression of M. incognita), and Delta and Pine Land DP458 B/R (susceptible standard, 0% suppression). Cotton was grown in fumigated and non-fumigated plots to measure yield loss. Each genotype and nematicide combination was planted in the same place for three years at two sites to document cumulative effects. In 2006, following three years of the different genotypes, all plots at one site were planted with susceptible cotton to document residual effects of planting resistant genotypes. Root galling and nematode population densities in the soil were significantly lower, and percentage yield suppression was numerically lower, when moderately resistant cotton was grown compared to the susceptible standard in both fields in all three years. Differences between susceptible and moderately resistant genotypes are established quickly (after only one season) and then either maintained at similar levels or slightly increased in subsequent years depending on initial nematode levels. However, when susceptible cotton was grown following three years of the moderately resistant genotypes, the nematode suppression provided by moderate resistance was undetectable by the end of the first season. Moderately resistant cotton genotypes are more beneficial than previously believed and should be pursued for their significant contribution to nematode management. Rotation of moderately resistant cotton and susceptible cotton could be used along with nematicides to manage root-knot nematodes in a continuous cotton cropping system and reduce selection pressure on the nematodes.