Masters Theses

Date of Award

8-1998

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Bonnie Ownley

Committee Members

Neil Quigley, Ernest Bernard, Bradford Reddick

Abstract

Take-all is the most destructive crown and root disease of wheat worldwide. It is caused by the soilborne ascomycete, Gaeumannomyces gramins var. tritici (Ggt). There are no economically-viable means of control or resistant wheat cultivars. Recent studies have demonstrated that bacterial isolates applied as seed treatments can reduce take-all disease severity significantly.

Six carriers in four concentrations, were tested at room temperature (25 C) and 4 C, for their ability to establish and maintain bacterial populations. Although results varied, methyl cellulose was associated with higher bacterial populations.

In a series of growth chamber cone assays, the carriers were examined for their effects on take-all disease development. In the first trial, there was a significant interaction between carrier and seed treatment on disease severity. Two isolates differed in biocontrol ability only when applied with Polysurf 67, which was associated also with significantly higher disease severity ratings. In the second trial no significant interactions were noted between carriers. This suggests that the carriers can affect disease development.

Bacterial isolates that displayed activity against Ggt in vitro were selected for study in a series of cone assays. The first series tested all ten isolates singly. The best isolates were selected for trial singly and in combinations for the second series. In the first trial of the single-isolate assay, six isolates were associated with significantly greater shoot heights than the control and five were associated with significantly lower disease ratings. In the second trial no significant effects were observed. In combination assays, no significant effects were observed in the first trial. In the second trial all bacterial treatments were associated with lower disease ratings than the control. This suggests that the isolates are effective biocontrol agents under certain conditions.

Three field studies were established. At the Knoxville site, stand counts (emergence) were increased by three treatments and decreased by two. Head counts (an indicator of plant vigor) were increased by three treatments. Yield (kg/plot) was decreased by one treatment. Test weight (grain plumpness) was decreased by one treatment. At the Springfield site, stand counts were decreased by five treatments. Head counts were increased by four treatments. Yield was increased by one treatment, and decreased by three. Test weight was increased by one treatment and decreased by one. Stand counts at the Jackson site were higher with one treatment. Head counts were higher with three treatments. Yield was increased with four treatments. Only one treatment was associated with a higher test weight.

The goal of this work was to further the development of an agronomically viable biological seed treatment for take-all by helping future researchers focus their time and resources. Towards that end, it is suggested that isolates MF102 and MB105 be selected for further evaluation because they appear to provide the most consistent control.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS