Biological control studies of reniform nematode in Alabama cotton crops

Abstract

Rotylenchulus reniformis is the most important pathogen of cotton in the southeastern United States. Aldicarb, which is the most used nematicide in cotton production, will be retired from the market in 2018 by the EPA. Thereby, this is the time to introduce biocontrol agents against R. reniformis that can reduce nematode damage on cotton plants. Several reports of fungi and bacteria antagonistic to R. reniformis have been published. The general objective of this research was to evaluate different commercial biocontrol agents, new formulations for biocontrol agents, and new antagonists that can be implemented to control R. reniformis in cotton crops. Specific objectives were: i) to evaluate the biocontrol potential of Bacillus firmus GB-126 and Paecilomyces lilacinus 251 under greenhouse, microplot, and field conditions against R. reniformis; ii) to understand the mechanisms of acton of B. firmus GB-126 under in vitro conditions; and iii) to identify morphologically and molecularly a new strain of Catenaria auxiliaris found paratizing R. reniformis. Reductions of all life stages of R. reniformis was observed with the combination of B. firmus (1.4x107 spores/seed) and P. lilacinus (0.3% v/v) under greenhouse cultivation 30 days after planting (DAP). The two biologicals reduce R. reniformis vermiform life stages at 60 DAP, and increased plant height and stem diameter in microplot and field trials. Cotton yields were similar between the biological B. firmus and P. lilacinus combination treatment and aldicarb. In vitro studies indicate that the mechanism of action of B. firmus works as a biosurfactant produced by the bacterium at concentrations of 1 and 2 ppm which paralyses the juvenile stages within 30 minutes in vitro. Further studies found Catenaria auxiliaris parasitized 42% of R. reniformis populations. This obligate-parasite fungus was identified based on the 18S and 28S rDNA. Catenaria auxiliaris has the potential of become a successful biocontrol agent because it colonizes all life stages of the nematode, zoospores give mobility to this biocontrol agent, and the resistant spore stage can extend the survival of the fungus in the commercial formulation process. At this time there are commercial biocontrol agents and new antagonists of R. reniformis that can be implemented in a nematode management program when aldicarb is removed from the market.