Identification and Characterisation of New Microbial Antagonists for Biocontrol of Monilinia laxa, the Causal Agent of Brown Rot on Stone Fruit

Abstract

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 OPEN ACCESSAgronomy 2013, 3 686 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.

Potential of a new strain of Bacillus amyloliquefaciens BUZ-14 as a biocontrol agent of postharvest fruit diseases

“…strains (Pusey and Wilson, 1984;Altindag et al, 2006;Yañez-Mendizabal et al, 2010;Liu et al, 2011;Rungjindamai et al, 2013;Gao et al, 2016). The high efficacy against brown rot of BUZ-14 endospores is very interesting as they are more stable than vegetative cells maintaining their viability for years and far more resistant to drying processes for powder formulations (Brannen and Kenney, 1997) Figure 3.…”

Phyllosphere Fungal Communities of Plum and Antifungal Activity of Indigenous Phenazine-Producing Pseudomonas synxantha Against Monilinia laxa

“…One of the first formulated postharvest biocontrol products, now widely used, BioSave TM (JetHarvest Solutions) is based on a saprophytic strain of Pseudomonas syringae active against number of postharvest decaying fungi, but not Monilinia . Many studies since than reported antagonists effective against M. laxa , including Aureobasidium pullulans (Mari et al, 2012; Rungjindamai et al, 2013; Di Francesco et al, 2017); Pantoea agglomerans (Bonaterra et al, 2003); and Bacillus amyloliquefaciens (Rungjindamai et al, 2013) as well as some Pseudomonas spp. (Altindag et al, 2006).…”

A novel strategy to reduce overwintering inoculum of Monilinia laxa

“…Indar inhibits sterol biosynthesis of M. laxa and directly targets the pathogen under most environmental circumstances. In contrast, biocontrol mechanisms of Y126 and B91 involve competition for nutrients and production of inhibitory compounds (Rungjindamai et al 2013), which are more likely to be influenced by external conditions. One of the challenges in biocontrol of plant pathogens is to fully understand the ecology of each BCA in order to optimise its application strategy under field conditions (Xu and Jeger 2013a, b).…”

“…This may be because Y126 can survive low temperatures better than B91 (Rungjindamai et al 2013) [note that a different isolate of the same Bacillus species is the active ingredient of Serenade]. Application of a formulated product of another A. pullulans strain during cherry blossom led to a significant reduction in the disease incidence (Holb and Kunz 2013).…”

“…For Indar and Serenade, application rates followed manufacturers' recommendations: Indar (2 ml/l) and Serenade (10 ml/l). B91 and Y126 were isolated from stone fruit in the UK and showed promising results against M. laxa when t e s t e d o n d e t a c h e d c h e r r y a n d p l u m f r u i t (Rungjindamai et al 2013). They were cultured in 100 ml of nutrient broth and potato dextrose broth, respectively, on a shaking incubator at 25°C at 200 rpm for 4 days.…”