is experimentally well established as a BCA against B. cinerea. It has shown good control of stem infection and only moderate disease control of leaf infection in tomato tomato crops grown in North East Scotland. To increase efficacy of disease control it was decided to combine its use with another Bacillus BCA. Since the principal mode of action of B. brevis is antibiosis via the antifungal metabolite gramicidin S then the selection stategy for the new BCA was based on it having a different mode of action. Screening numerous Bacillus isolates from the above work identified the B. amyloliquefaciens as a likely candidate. Unlike B. brevis the B. amyloliquefaciens BCA did not show antibiotic zones of inhibition against B. cinerea in vitro but did have effective control grey mould disease. Since the two Bacilli used separately have moderate-good disease control levels and act against B. cinerea by different mechanisms then combined treatment was tested for control of grey mould in planta to determine if additive or synergistic disease control could be achieved. It was found that not only did combined use lead to increased efficacy of disease control but high level control was achieved even with much lower concentrations of the combined BCAs suggesting that indeed synergistic effects were operative. This again indicated that the individual BCAs acted at different sites and/or by different mechanisms in their mode of action. These observations promise the possibility of using the BCAs in combination at lower levels yet with increased efficacy of disease control of B. cinerea and reduced risk of resistance development in the pathogen.
Development of the BCA Bacillus Brevis for Biocontrol of Grey Mould: In Planta Mode of Action Studies with Lettuce and Tomato.
Rosalind McHugh and Barrie Seddon, School of Biological Sciences, College of Medical and Life Sciences, Hilton Campus, University of Aberdeen, Aberdeen, AB24 4FA, Scotland, UK
Bacillus brevis strain Nagano produces the cyclic decapeptide gramicidin S shown in vitro to have antifungal activity against Botrytis cinerea. Additionally a biosurfactant is also produced that reduces periods of leaf wetness required for germination of conidia of this pathogen. These attributes seem ideal for the development of B.brevis as a BCA against grey mould disease since the demonstrated presence of at least two different modes of action for biocontrol has the potential to lead to greater efficacy of disease control with reduced risk of resistance development in the pathogen. Using lettuce and tomato crops grown in polytunnels and carrying out studies with the gramicidin S producing wild-type strain of B.brevis and a gramicidin S–negative mutant E-1 the progress of grey mould disease was followed in both crops and the degree of disease protection achieved was monitored in each situation. A scenario was developed for effective disease control of B.cinerea using B.brevis based on a knowledge of the interplay of the modes of action operating and the crop and prevailing environmental conditions. These observations in lettuce and tomato crops indicate that it should be possible to develop similar scenarios with other crops using the B.brevis BCA. Indeed such detailed trial studies to establish the influence of the environment on the contribution of each mode of action to disease control are necessary before commercial application of any BCA is attempted if the delivery of effective biocontrol systems is to progress.
Plenary talk 4
Integration of classical and molecular approaches to successfully control clubroot of crucifers
Ian Porter1, Caroline Donald1, Rachel Lancaster2, and Robert Faggian1
1 Department of Primary Industries, Knoxfield, PMB 15, Ferntree Gully DC, 3156, Victoria, Australia 2 Department of Agriculture, Western Australia, PO Box 1231, Bunbury, 6231, Western Australia, Australia.
Clubroot, caused by Plasmodiphora brassicae, has been a constant cause of crop loss in crucifers in Australia since 1890. Crop loss to the disease however, increased dramatically in the 1980’s due to the use of transplant modules, which narrowed crop rotations and enabled growers to increase crop intensity (4 crops/year). The disease also threatened a A$30 million cauliflower export market industry in Western Australia. To address this, an integrated program to control and prevent the spread of clubroot has been developed. This is based on detection and quantification of P. brassicae, improved farm and nursery hygiene and strategic application of in-field controls using combinations of ground burnt lime (calcium oxide), calcium and boron fertilisers and the fungicide fluazinam. A nested PCR assay has enabled accurate identification of clubroot DNA (spores) in dust, water and in roots of ‘clean’ transplants. This has enabled identification of sources of contamination on farm (from dams and rivers) and in nurseries (trays, dust, screen covers) and therefore