Date of Award

5-2008

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Seanna L. Annis

Second Committee Member

David H. Lambert

Third Committee Member

Christa R. Schwintzer

Abstract

In 2005, a "new" leaf spot disease that produced red-brown lesions which spread from the edge of the leaves down to the petiole was found on lowbush blueberry (Vaccinium angustifolium). Several fungi associated with infected plants were isolated, identified and then inoculated onto leaves and stems to determine if they were the causal agent of the leaf spot. Bactrodesmium, Botrytis, Cladosporium, Gloeosporium, Phompsis, and Pestalotia were isolated from symptomatic leaves and Acremonium and Gliocladium were isolated from the rhizomes of symptomatic plants. Of these fungi, Gloeosporium, Pestalotia and Phomopsis isolates produced dark lesions starting on the edges of leaves in preliminary trials and were subsequently tested in detached leaf trials and the ITSl, 5.8S, and ITS2 regions of ribosomal DNA were sequenced to confirm their identity.

Gloeosporium was not pathogenic on lowbush blueberry, since inoculated leaves did not have higher symptom incidence or severity than control leaves. Gloeosporium was reisolated from control and Gloeosporium-moculated leaves. The two Gloeosporium isolates obtained shared little similarity in their ITS regions since one matched with known Phacidiopycnis species and one with Discula species.

Pestalotia was weakly pathogenic on lowbush blueberry leaves which developed large water-soaked lesions that turned brown. Leaves inoculated with one of two Pestalotia isolates had higher symptom incidence than the controls, and leaves inoculated with either of the two Pestalotia isolates developed symptoms that were significantly more severe (P<0.001) than those found on control leaves. Pestalotia was also reisolated from both Pestalotia-inoculated and control leaves. The five Pestalotia obtained isolates had identical sequences and matched those of known Pestalotiopsis species.

The single Phomopsis isolate inoculated on lowbush blueberry leaves was pathogenic and caused light brown lesions with dark edges or turned the leaves red. The Phomopsis-inoculated leaves had significantly higher symptom severity in comparison with control leaves (P<0.006) in three of four trials, but symptom incidence was not significantly different. Phomopsis was only reisolated from Phomopsis-inoculated. leaves. The eleven Phomopsis isolates obtained fit into four groups by their ITS region and matched those of known Phomopsis/Diaporthe species. Pestalotia and Phomopsis were confirmed as pathogens of lowbush blueberry, but the causal agent of the "new" leaf spot disease was not identified in this study.

The sensitivity of mycelial growth and spore germination of two isolates each of Pestalotia and Gloeosporium to the fungicides chlorothalonil (Bravo), fenbuconazole (Enable), and propiconazole (Orbit) and the biological control materials containing Bacillus subtilis (Serenade) and B. pumilis (Sonata) were examined in vitro. Bravo was the most effective of the three fungicides at inhibiting spore germination, as 1 ppm inhibited germination by 100% of all isolates. Orbit was the most effective of the 3 fungicides at inhibiting mycelial growth, as 1 ppm significantly inhibited at least 70% of the growth (p<0.05) of all isolates compared to the controls. Serenade was the most effective biological control product tested against Pestalotia and Gloeosporium.

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