Recipient Organization
TEXAS A&M UNIVERSITY
750 AGRONOMY RD STE 2701
COLLEGE STATION,TX 77843-0001
Performing Department
Plant Pathology & Microbiology
Non Technical Summary
Research from my previous Hatch project identified an effective fungicide, Topguard (flutriafol), to control cotton root rot, caused by the fungus, Phymatotrichopsis omnivora. However, there is a need for research to further refine this innovation. First, there is occassional phytototoxicy associated with its use, so I propose to study factors that lead to this phytotoxicity, in order to devise recommendations to reduce or prevent it. Second, there have been problems applying the fungicide at planting, so I propose to evaluate different methods of application and communicate recommendations to the farmers. Finally, I will attempt to determine the site of action of the fungicide and this knowledge could lead to improvements in management of this disease, and perhaps, other diseases.
Animal Health Component
40%
Research Effort Categories
Basic
40%
Applied
40%
Developmental
20%
Goals / Objectives
1. Evaluate approaches to prevent or ameliorate phytotoxicity of Topguard Terra to cotton.2. Evaluate different methods of application of Topguard Terra for Phymatotrichum root rot control.3. Evaluate the site of action of the fungicide, specifically root vs. rhizosphere.
Project Methods
Objective 1: The first step will be to develop a reliable in vitro and growth chamber system to induce phytotoxicity with Topguard Terra exposure. Soil types representing several cotton growing areas of Texas will be used, but emphasis will be placed on soils from fields where phytotoxicity has been reported. These soils will be treated with different concentrations of Topguard Terra (ranging from 100 µg/g a.i. to 10,000 µg/g), planted to different varieties of cotton, and incubated under controlled temperature and soil moisture (Couch et al., 1967). A growth chamber is available for this work and soil moisture (matric potential) can be controlled using a Haines apparatus (Haines, 1930). These experiments will simulate sub-optimal planting conditions that have been associated with phytotoxicity, i.e. cool soil temperatures and increased moisture following planting.Experiments will be conducted with soilless systems for inducing phytotoxicity with Topguard Terra. A blotter assay technique will be used to evaluate the response of different varieties and seed quality to Topguard Terra treatment. Seed germination paper will be saturated with different concentrations of Topguard Terra and cotton seeds incubated in them at low (68 ºF) and high (86 ºF) temperatures. The dry weights of roots of germinated plants will then be measured. This technique allows the determination of direct interactions between the fungicide and the seed under a controlled environment and will complement experiments conducted by germinating seed in soil under similar controlled environments.Once soil and soilless systems have been developed, safeners can be evaluated for their ability to ameliorate phytotoxicity. Objective 2: The focus will be on post-plant applications. The experiments will be done in different locations in the state, representing different production practices. Although there will be variation in rates and methods among the experiments, all experiments will include the 4 fl.oz./A rate of Topguard Terra applied as a T-band, the currently-labeled low rate.Specific treatments include flutriafol application as a T-band, and as a top band i.e.sprayed onto the soil after planting, either on the day of planting or various time intervals (every two weeks) afterwards, up to pin head square growth stage. Treatments will be applied to 4 rows X 50 to 100 feet. Each treatment will be replicated four times in a randomized complete block design. The experiments will be conducted in commercial fields in San Patricio, Williamson, Hill, Tom Green, and possibly other counties, if opportunities arise. The Texas AgriLIFE Extension Stiles Foundation Farm in Thrall has a non-irrigated block with PRR. Moisture and temperature at planting and during emergence will be continuously monitored in most fields. Observations will be made to detect any phytotoxicity, and in particular, delays in emergence. If any phytotoxicity is evident, soil samples will be collected for laboratory and greenhouse experiments. Phymatotrichum root rot incidence will be measured, at least once during the growing season and at the end of the season, as well as the yield. A chemical analysis of flutriafol concentration will also be done with some of these soil samples.Objective 3: This will be done as a growth chamber study. Sclerotia or mycelial strands of P. ominvora, carried on the surface of porous, polycarbonate membranes, will be placed on Petri plates with soil containing different concentrations (ranging from 100 µg/g a.i. to 10,000 µg/g) of Topguard Terra. The membranes will be removed from the soil and stained in phenolic rose Bengal. The growth of the mycelia will be measured with a microscope. Additionally, cotton seedlings grown in sand treated with several concentrations of Topguard Terra will be transplanted to petri dishes withsoil. They will be laid laterally on the soil and covered with a polycarbonate membrane. Growth of P. omnivora from a point distant from the root across the membrane will be measured as previously described, and colonization of roots will be evaluated by removing them and staining them. These experiments will be conducted at 35° C, which is a temperature that fosters rapid growth of P. omnivora. With this design, experiments can be conducted in 2-3 days. Initially, experiments will be conducted near soil saturation, but subsequently, a Haines apparatus will be used to set and keep a constant soil matric potential. This experiment will be conducted with at least two different soil types, a clay loam and a sandy loam.