Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Plant Science (PhD)

Degree Level

Graduate

Department

Plant Pathology

Advisor

Terrence L. Kirkpatrick

Committee Member

Scott Monfort

Second Committee Member

Kristofor R. Brye

Third Committee Member

Douglas Karcher

Abstract

The root-knot nematode, Meloidogyne incognita, and the seedling pathogen, Thielaviopsis basicola, commonly co-exist in Arkansas cotton fields and may interact resulting in increased losses. The primary objective of this research was to evaluate the effects of soil physical parameters on these soilborne pathogens and cotton growth in controlled environmental, field, and microplot studies. Controlled environmental experiments used two soil bulk densities and four pathogen treatments: non-infested soil, soil infested with M. incognita or T. basicola and soil infested with both pathogens. The results indicated bulk density generally did not affect seedling growth or disease since soils had low penetration resistance under well-watered conditions. The combination of M. incognita with T. basicola reduced seedling stands and root volume more than either pathogen alone. Both M. incognita and T. basicola reduced root topological characters, but only M. incognita changed the root topological index. The effects of subsoiling and application of the nematicide 1,3-dichloropropene (Telone II®) on root system development and plant growth were investigated from 2009 to 2011 in a cotton field in northeastern Arkansas. Subsoiling did not consistently affect early season growth. Nematicide treatment consistently improved seedling growth for one or more parameters in 2010 and 2011. Root galling and the population of M. incognita were suppressed by Telone II®. Neither subsoiling nor nematicide application affected cotton development or root topology. The effects of a soil hard pan (HP) and M. incognita on cotton root architecture and plant growth were evaluated in a microplot study in 2010 and 2011 at Hope, Arkansas. An artificial HP was created 20 cm below the soil surface in half of the microplots. Pathogen treatments included soil infested with T. basicola plus four different M. incognita levels (0, 4, 8, 12 eggs/cm3 soil). Generally, soil HP improved seedling growth due to higher soil water contents above the HP layer. M. incognita reduced taproot length, delayed cotton maturity and reduced seed cotton yield. Root topology provides a new approach to quantify the changes caused by soilborne pathogens and soil physical factors and will help in crop management in the future.

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