Pathogen Profile #13

Hello Robigalia Reader and welcome back to another week of Robigalia, delivering the latest in plant pathology directly to your inbox!

Recently I introduced you to Botrytis fabae which causes disease on faba beans. In my reading, I couldn’t ignore the vast amount of research on the closely related and highly destructive Botrytis cinerea which causes grey mould on strawberries. It turns out strawberry fields may not be forever in the face of this fungus. Scroll down to read this week’s article. If you’re a Robigalia subscriber you can also access my online database and today’s title song!

Botrytis cinerea is a necrotrophic fungus belonging to the family Sclerotiniaceae. Causing grey mould on a wide range of host plants, the pathogen was first described in 1771. Derived from the Latin for “grapes like ashes”, it gained its name from the first reports of grey mould on grapes. Today, B. cinerea is known to infect over 400 host species and is considered the primary fungal pathogen of harvested strawberries (Fragaria × ananassa) worldwide.

Botrytis cinerea thrives in cool, moist environments, making it a common threat in coastal and temperate regions. The fungus primarily spreads through asexual conidia, which spread by wind and water. These spores can infect plant tissues through wounds, and natural openings such as stomata or directly penetrate the epidermis.

The life cycle of B. cinerea on strawberries involves several stages. During primary infection, the fungus infects strawberry flowers. Conidia germinate in the stigmatic fluid, allowing fungal hyphae to grow into the flower's reproductive organs. The fungus then typically enters a quiescent phase of limited growth before the fruit ripens. The limited resources lead to minimal fungal activity during this stage and no visible symptoms. As the fruits ripen and sugar levels increase, the active infection phase begins. Here, the fungus resumes activity and rapidly colonises the fruit leading to characteristic grey mould development, which can destroy the berry within 48 hours under favourable conditions.

The United States is the largest producer of strawberries globally, followed by Mexico and Egypt. In Florida, grey mould caused by B. cinerea causes significant crop losses, with reports of losses exceeding 50%. In addition to reducing yields, grey mould continues to affect strawberries post-harvest and is the most common post-harvest disease of strawberries. Leading to decay during storage and transport, not only does grey mould reduce the marketable yield but also affects the quality and shelf life of the fruit, resulting in further economic losses.

The primary method of controlling grey mould involves the use of chemical fungicides. In addition to adding significant costs to production, heavy fungicide reliance has led to the establishment of fungicide-resistant strains of B. cinerea. Studies have identified B. cinerea strains with multiple drug resistance, where strains develop resistance to a broad range of unrelated fungicides after exposure. The development of resistance requires the use of newer, often more expensive fungicides, further increasing production costs.

Effective management of B. cinerea involves a combination of cultural practices and biological controls alongside fungicides. Ventilation and mulching are two common practices to reduce incidences. Ventilation reduces humidity, thus reducing the favourable conditions of disease establishment, while mulching prevents soil contact with berries to reduce infection risk. Certain bacteria and fungi have shown promise in controlling B. cinerea by outcompeting or directly inhibiting the pathogen.

If you’re interested in diving into the science of B. cinerea, I’ve summarised a few articles below. Robigalia subscribers can scroll down to access my online database, which includes full summaries of these and all other featured Robigalia articles.

Botrytis cinerea papers

Detection of Botrytis cinerea on strawberry leaves upon mycelial infection through imaging technique

• This study explores the use of multispectral imaging for the early detection of B. cinerea on strawberry leaves. By assessing chlorophyll fluorescence and the modified anthocyanin reflection index, researchers identified sensitive indicators that can facilitate timely and effective disease management.

Multidrug resistance of Botrytis cinerea associated with its adaptation to plant secondary metabolites

• This study investigated multidrug resistance (MDR) in B. cinerea through preadaptation to plant secondary metabolites (PSMs). The research found continuous exposure to PSMs like resveratrol and eugenol led to the upregulation of ABC transporter genes, which increased the pathogen's resistance to various fungicides.

Botrytis cinerea combines four molecular strategies to tolerate membrane-permeating plant compounds and to increase virulence

• Recent research has identified four distinct mechanisms that B. cinerea uses to tolerate saponins, toxic plant defence compounds, thereby enhancing its virulence on strawberry plants. The study discovered a novel saponin-degrading enzyme and three additional intracellular mechanisms that help the fungus withstand membrane damage caused by saponins, providing insights that could inform new strategies for crop protection and fungal pathogen management.

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Until next week,

Alyssa