Biocontrol as a key component to manage brown rot on cherry

Brown rot, caused by Monilinia spp., is one of the most important diseases in stone fruits worldwide. Brown rot can cause blossom wilts and fruit rots in the orchard as well as latent infections of fruit, leading to post-harvest fruit decaying. Current control methods rely on scheduled spraying of fungicides. However, the continuing pressure to reduce fungicide use has seen an increase in research into alternative management methods, such as biological control. NIAB EMR recently identified two microbes that significantly reduced sporulation of Monilinia laxa under laboratory conditions. These two isolates were a bacterial species Bacillus subtilis (B91) and yeast-like fungus Aureobasidium pullulans (Y126) and are currently being formulated into commercial products. We are investigating how to optimise the use of these two potential biocontrol products in practice, in terms of suppressing Monilinia sporulation on overwintered mummies and preventing infection of blossoms and fruits. When applied to mummified fruits in winter Y126’s population was stable through the winter but at a low concentration. The B91 survived a little longer with the population reaching that of the control group by week 4. Neither Biological control (BCA) treatments had an affected the population of M. laxa when compared to the control treatment of sterile distilled water. The interaction time between the BCAs and M. laxa showed the longer the interaction time the lower the spore count of M. laxa. Another study was performed looking into the ability of our BCAs to colonise and survive on blossoms. B91 did not survive well on blossoms but could survive on fruits. However, its antagonistic compounds need to be in relatively high concentration to be effective against M. laxa. Therefore, it is best used as a fungicide, ensuring the antagonistic compounds are at a high concentration when applied in the field. Y126 can persist throughout the season and was marginally, though not statistically significantly, more effective at long term reduction in M. laxa. This could be because Y126 works through competition, therefore the interaction time with the pathogen could be important for efficacy and something worth investigating further. The difference between the BCAs highlights the need to understand each BCA’s ecology to ensure maximum efficacy. In a latent infection experiment, we inoculated trees with M. laxa and then treated them with the two biocontrol isolates two weeks before harvest. Post-harvest disease development was assessed after four days of storage in 2019 and two weeks in 2020. There was a significant reduction in rot incidence (p < 0.001) of 29% (Y126) and 27% (B91) in 2019 and 62 % (Y126) and 80 % (B91) in 2020 when the harvested fruit was stored at cold store levels. With new products to be introduced into the environment, it's important to understand the effects they may have on the plant's microbiome. Using next-generation sequencing techniques, we looked at the impact B91 and Y126 has on the blossom and cherry microbiomes. There was a treatment effect in both the bacterial and fungal communities on the blossom and ripe cherry. But the biggest variability was between blocks (Geographical effect) and between the years in which we experimented (p < 0.0001). This research will assist in the development of management strategies, especially spray timings for brown rot on stone fruit, integrating BCAs with other management practices