• Distribution and Genetic Variability of Whitefly-Transmitted Geminiviruses of Cotton

      Brown, J. K.; Silvertooth, Jeff; Department of Plant Sciences, University of Arizona, Tucson, Arizona (College of Agriculture, University of Arizona (Tucson, AZ), 1996-03)
      Whitefly-transmitted geminiviruses (subgroup III, Geminiviridae) are emerging viral pathogens of cotton, worldwide. Virtually nothing is known about the genetic variability, biological characteristics, or the molecular epidemiology of these new virus pathogens of cotton. The core region (550bp) of the geminiviral coat protein gene was examined as a potentially informative molecular marker by which to identify and track the global distribution of WFT geminiviruses of cotton. This is an essential step toward assessing the risks that emerging viruses pose to cotton production efforts. Preliminary analyses of geminivirus isolates from North America, Central America and the Caribbean Basin, and Sudan indicate that the core region of the coat protein gene permits predictions about relationships between virus isolates from cotton, based on subgeographical and major geographical origins, and has potential for distinguishing between geminiviral quasi-species and virus strains, thereof Through these efforts, a database of geminivirus coat protein gene sequences has been established to permit identification of additional isolates from cotton, and to facilitate the tracking of WFT geminiviruses for molecular epidemiological and subsequent risk assessment objectives. Using the latter information, it will become possible to identify the most important geminiviruses against which disease resistance efforts should be directed. Further, the availability of a broad suite of cotton geminivirus isolates from both Eastern and Western Hemispheres will permit assessment of cotton germplasm and/or genetically engineered lines for virus-specific and/or broad spectrum disease resistance for the first time.
    • Magnitude and Strain Composition of Aspergillus flavus Soil Surface Populations in Yuma County Commerical Fields

      Nelson, M. R.; Bigelow, D. M.; Orum, T. V.; Howell, D. R.; Cotty, P. J.; Silvertooth, Jeff; Department of Plant Pathology, University of Arizona, Tucson; Cooperative Extension Service, University of Arizona; Southern Regional Research Center, USDA, ARS (College of Agriculture, University of Arizona (Tucson, AZ), 1996-03)
      Aflatoxin contamination of cottonseed occurs when cotton bolls are infected by certain strains of the fungus Aspergillus flavus. The risk of aflatoxin contamination in a field is partially dependent on both the quantity of A. flavus and the toxigenicity of A. flavus strains in that field. A. flavus can be easily divided into two major subdivisions known as strain S and strain L. Strain S isolates consistently produce large amounts of aflatoxin and, therefore, the percentage of strain S isolates in the population (percent S) is one indication of the aflatoxin producing potential of the population. Strain S isolates were found in every commercial field sampled at every sampling date in Yuma County, but percent S varied greatly among fields from 4% to 93 %. Significant differences among fields located near each other suggest that locally important, but not yet identified, variables such as crop rotation histories or soil type are affecting A. flavus population magnitude and composition.
    • Telone II® and Temik® Efficacy on Root-knot Nematodes in Cotton

      Husman, S.; McClure, M.; Deeter, B.; Silvertooth, Jeff (College of Agriculture, University of Arizona (Tucson, AZ), 1996-03)
      A field plot in western Maricopa county was established in 1995 to determine the ability of Temik® brand aldicarb pesticide to suppress root-knot nematode when Temik 15G was applied as a seedling side-dress and moved into the root zone by irrigation. Telone II® was used for comparative purposes and Gaucho-treated seed, following a preplant application of Telone, was included to determine if additional benefits could be realized by systemic control of insects during early stages of plant growth. Plans to include foliar applications of Orthene® were abandon when early season thrips populations failed to develop. Temik 15G, applied as a side-dress at 10 lbs. did not suppress nematodes or increase lint yield Telone, alone and in combination with Gaucho -treated seed, reduced nematode populations and increased lint yield, but differences between the two Telone treatments were not significant. Insect pressure was not a contributing factor. Greenhouse studies showed that both timing of the application and its placement in the row will be of critical importance when Temik is applied for nematode control in furrow irrigated cotton.