Biological control of chocolate spot and rust on faba beans

Jackson, Andrew James (1993) Biological control of chocolate spot and rust on faba beans. PhD thesis, University of Glasgow.

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Abstract

The potential of bacterial and fungal isolates from root and soil samples of faba bean and other crops, was assessed for biological control of Botrytis fabae (chocolate spot) and rust (Uromyces viclae-fabae) through in vitro and in vivo screening. In total, 690 bacterial and fungal isolates were obtained and screened with B. fabae mycelium in a preliminary screen on agar plates. Potential antagonism was exhibited by approximately 30% of these isolates, as indicated by at least one of the following visual symptoms: a brown discoloration of mycelium or media, a zone of inhibition of mycelial growth, a zone free of sclerotial formation or contact inhibition between isolates. Detached leaf studies rejected a further 20% of the isolates due to their pathogenicity towards the leaves. Further replicated antagonism tests in vitro allowed more detailed studies, where the percentage inhibition in radial growth of B. fabae and the zone of inhibition were recorded. Some isolates which exhibited potential antagonism in the initial preliminary screen did not do so in this test. Bacterial isolate LL1.F23, identified as Pseudomonas fluorescens, exhibited the largest inhibition zone (11.2 mm), inducing malformations and severe browning of mycelium at the culture edge. Overall, fungi produced smaller inhibition zones than bacterial isolates. Germination tests with B. fabae conidia showed that isolate LL1.F23 significantly reduced the germination, length of germ-tubes produced and appressorium formation relative to the control. Other isolates reduced germination significantly but to a lesser degree. Some fungal isolates inhibited mycelial growth of B. fabae through the production of volatile and nonvolatile antibiotics. However, due to the production of secondary colonies of antagonists, the results were variable and inconsistent. Spore germination tests on V. viclae-fabae in the presence of antagonists showed that uredospore germination was reduced by up to 90%. Following in vitro screening, 35 isolates (15 fungal and 20 bacterial isolates) were chosen for application to bean plants in the glasshouse. Against chocolate spot, the fungal isolate AP1.S20 (Penicillium chrysogenum Thom.) showed the greatest potential, reducing disease levels by up to 80%. Fungal isolate AG1.F4 (Geomyces pannorus (Link) Singler and J.W. Carmich.) and bacterial isolate P1.S13B, reduced chocolate spot infection to 19% and 12% of the control respectively, when applied simultaneously with B. fabae conidia. The percentage leaf area covered with rust pustules was reduced by 78% following simultaneous application of isolate AP2.R16 with rust uredospores. The most consistent reductions in chocolate spot and rust were obtained with simultaneous inoculation of the antagonist and the pathogen. It was found with rust that the greater the concentration of antagonist inoculum, the greater the reduction of rust on the leaf surface. A suspension of 1 x 10.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Dale R Walters
Keywords: Plant pathology
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-72291
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 24 May 2019 15:12
Last Modified: 24 May 2019 15:12
URI: http://theses.gla.ac.uk/id/eprint/72291

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