Abstract
Monilinia laxa is the causal agent of brown rot disease on stone fruits, and also causes blossom wilt and twig canker. The common practice used to manage this disease is through fungicide treatments. However the demand to reduce fungicide inputs has been increasing and there is a growing number of reports of M. laxa strains that are resistant to fungicides. There is an urgent need to search for an alternative strategy to control the disease. This study focused on the isolation and characterisation of biological control agents (BCAs) using indigenous isolates isolated from cherries and plums collected within the UK. A total of 192 isolates were screened against two strains of M. laxa in a series of in vitro dual culture tests. From this in vitro screen, 12 isolates were selected for a subsequent in vivo screen on detached fruits, which then narrowed these isolates down to two potential BCAs. These two strains were identified as Bacillus amyloliquefaciens/subtilis (isolate B91) and Aureobasidium pullulans (isolate Y126). The capability of these two potential BCAs to grow and survive at a range of temperatures likely to be experienced under field and storage conditions was studied in order to gain knowledge for product formulation and field application. Bacillus sp. B91 was shown to be a mesophilic bacterium that could grow at 10–25 °C but suffered significant mortality at 0 and 5 °C, while A. pullulans Y126 was both mesophilic and psychrotolerant as it grew between 0–25 °C with the optimum at 20 °C. When all nutrients were removed, Y126 was able to survive for several weeks in all test temperatures (0–25 °C) but showed significant mortality at 25 °C. The capability of B91 to survive at 20 and 25 °C was higher than at low temperatures (0–15 °C). In addition, the modes of action of the potential BCAs were studied. B91 was shown to produce soluble and volatile organic compounds that inhibited M. laxa, while A. pullulans Y126 did not produce inhibitory compounds, but appeared to inhibit the pathogen via competition for nutrients. This study shows that microbial antagonists against M. laxa can be found from indigenous sources and that they are capable of preventing brown rot disease in controlled conditions, thus demonstrating a potential to be developed into commercial products.
Highlights
Important stone fruit species of Prunus include peach (P. persica var. persica), nectarine (P. persica var. nucipersica), apricot (P. armeniaca), plum (P. domestica) and sweet cherry (P. avium)
This study shows that microbial antagonists against M. laxa can be found from indigenous sources and that they are capable of preventing brown rot disease in controlled conditions, demonstrating a potential to be developed into commercial products
There was a positive relationship between inhibition of fungal mycelia on malt extract agar (MEA) and potato dextrose agar (PDA), the levels of inhibition on MEA were generally higher (40%–80%)
Summary
Important stone fruit species of Prunus include peach (P. persica var. persica), nectarine (P. persica var. nucipersica), apricot (P. armeniaca), plum (P. domestica) and sweet cherry (P. avium). In the last two decades, biological control agents (BCAs) have been increasingly studied worldwide and used to control brown rot disease, with most research focusing on M. fructicola [9,10,11,12,13] on peaches and nectarines. These studies have focused on bacteria [14], yeasts [11] and filamentous fungi [15], alone or integrated with physical methods [16]. Specific objectives were (1) to obtain indigenous isolates and screen them for inhibitory activity against M. laxa; (2) to identify potential biocontrol isolates; (3) to study growth and survival of potential biocontrol isolates at a range of temperatures likely to be experienced in the biocontrol environment; and (4) to understand the modes of actions of the potential biocontrol isolates in inhibiting spore germination and mycelial growth
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