Masters Theses

Date of Award

5-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Bonnie H. Ownley

Committee Members

Ernest Bernard, Craig Canaday, Kimberly Gwinn

Abstract

In greenhouse and growth chamber studies, thirteen species of bacteria (twelve Bacillus species and one Pseudomonad), and the entomopathogenic fungi, Beauvaria bassiana, were tested for their potential as biocontrol agents of Rhizoctonia solani on tomato. The bacteria were also tested for their ability to promote the growth of greenhouse-grown tomato seedlings. With only a few exceptions, the bacterial isolates did not reduce disease severity caused by R. solani, nor did they promote the growth of tomato seedlings. In the initial smdy, several seed treatments reduced disease severity caused by R. solani, however, only isolate E21 reduced disease in both trials. None of the isolates increased the height or weight of seedlings. Bacterial soil drenches were also ineffective in reducing disease severity. The disease ratings of plants receiving bacterial soil drenches were not different from the infested control plants in either trial. In Trial 1, when compared to the untreated, infested and uninfested controls, several of the bacterial soil drenches increased plant weight. In Trial 2, several isolates increased plant weight when compared to the untreated, infested control, but not when compared to the infested phosphate buffer saline control. In the second study, treatment with isolates BA77, BAlOl, or E726 had little overall effect on plant growth or disease. However, there was a significant host effect. Pre-emergence damping-off of 'Mountain Pride' seedlings was significantly less than seedlings of 'Celebrity' or 'Mountain Spring'. Plant stand counts of 'Mountain Pride' were 27 and 73% greater than 'Celebrity', and 35 and 75% greater than 'Mountain Spring', in Trial 1 and 2, respectively,. There were several interactive effects between BAlOl treatment and the cultivar 'Mountain Spring', but only in Trial 1. Stand counts of BAlOl treated 'Mountain Spring' seeds were 70% greater than the untreated, infested control, and were 87% of the uninfested control. In addition, BAlOl treatment significantly reduced disease severity on surviving 'Mountain Spring' seedlings. The average canker rating on BAlOl treated 'Mountain Spring' seedlings was 2.19, as compared to 3.44 on the untreated, infested control. In the final study, bacterial treatments applied to neutralized 'Mountain Spring' and/or 'Mountain Pride' seeds had little effect on subsequent plant growth or disease severity in R. solani infested soil. The shoot and root weights were little effected by the bacterial treatments in either experiment. The shoot weight of E69 treated plants was greater than the infested control, but only in Trial 1 of Experiment 1. Though treatment with isolates E21, BA77, and E69 increased plant stand in Trial 1 of Experiment 1, they did not increase stand counts in Trial 2, and none of the bacterial isolates increased stand counts in Experiment 2. Beauveria bassiana (BAV) treatment increased shoot weights of seedlings in Trial 1 of Experiment 1, but not in Trial 2, and did not effect root or shoot weights in Experiment II. However, treatment with BAV reduced pre-emergence damping-off of tomato seedlings in both trials of both experiments. In Experiment I, BAV treatment increased plant stands by 71 to 100% when compared to the infested controls. In Experiment II, when compared to the untreated, infested control, BAV treatment increased plant stands by 129 and 350% in Trial 1 and 2, respectively. BAV treatment did not effect the canker rating of surviving plants in trials of experiment II. Plant stands of 'Mountain Pride' were significantly greater than stands of 'Mountain Spring' in Trial 1 (+49%) and Trial 2 (+33%) of Experiment I. The differences were due almost entirely to differences in the infested treatments. Stands of 'Mountain Pride' in the untreated, infested control were 75 and 172% greater than comparable stands of 'Mountain Spring' in Trial 1 and 2, respectively. The effect of BAV treatment on plant stands of the untreated, infested control was also significantly different for the two tomato cultivars. BAV treatment increased plant stands of untreated, infested 'Mountain Pride' seeds by 57% in Trial 1 and 50% in Trial 2. However, BAV treatment increased comparable stands of 'Mountain Spring' by 187 and 236%, in Trials 1 and 2, respectively.

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