Grey mould causes great yield losses to strawberry farmers, retailers, and consumers. However, the beneficial fungus Aureobasidium pullulans is a promising biocontrol agent which can mitigate this plant disease. SLU researchers have, in a field study, shown that this beneficial fungus reduces grey mould severity after harvest and increases shelf life of the harvested strawberries. They have also investigated the mechanisms behind the biocontrol.
Strawberry is the economically most important soft fruit crop in Sweden, but great losses are caused each year by grey mould. Several different chemical fungicides are used against grey mould, but unfortunately this harmful pathogen has developed resistance to almost all chemical-based plant protection products. Therefore, novel and reliable biocontrol agents are needed to replace the chemical fungicides.
– The yeast-like beneficial fungus Aureobasidium pullulans has previously exhibited great potential to combat grey mould in greenhouse environments, says Mudassir Iqbal, researcher at SLU.
In a new study, two different concentrations of this beneficial fungus and sugar beet extract were tested during a two-year long field trial in Skåne. Sugar beet extract is a cheap raw material that contains bound polyphenols and other impurities from the plant. It has previously been shown to induce plant defense in potato.
– All the field treatments reduced grey mould severity after harvest and increased shelf life of the harvested fruit. We got the best effect with the highest concentration of A. pullulans, which also resulted in higher fruit production. This shows that the beneficial fungus also has plant-growth promoting effects, says Johan Stenberg, another SLU researcher behind this study.
Spray applications of both A. pullulans and sugar beet extract contribute to reliable biocontrol of grey mould and thus improved shelf life of strawberry sales boxes.
– Using this beneficial fungus or sugar beet extract can contribute to a shift from chemical fungicides to sustainable methods without compromising cropping security, says Mudassir.
What causes the biological control effect? In another study, A. pullulans were evaluated in the laboratory against the pathogenic fungi Botrytis cinerea and Colletotrichum acutatum, that cause grey mould and anthracnose diseases in strawberry.
Mycelial growth of the two pathogenic fungi was reduced when challenged with A. pullulans. Culture filtrates of A. pullulans also reduced mycelial biomass, indicating that metabolites are involved.
– Our study also showed that A. pullulans produced substantial amounts of extracellular proteases, which are known to degrade fungal cuticle. We took a closer look at the proteins and found exophilins, liamocins and free fatty acids, all known to have antifungal properties. We still need more studies to clarify exactly which metabolites that are responsible for the biological control effect, says Johan.
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