Wednesday, April 17, 2024

How can one fungus infect nearly all plants, vascular or not?

Two views of a common mould summarised from research by Ritu Singh, Celine Caseys and Daniel J. Kliebenstein in the news from the British Society for Plant Pathology, and also from Levantine Hill Wine articles.

If you observe signs of decay on your fruits and vegetables, accompanied by the growth of fuzzy grey-brown mould, chances are it is Botrytis cinerea. It’s a cosmopolitan fungus that infects more than 1500 plant species, ranging from dicots, monocots, and gymnosperms, to even non-vascular plant species. Both individual isolates and the species show this extensive host range is in contrast to other broad-host pathogens with narrow-range isolates. Key hosts include important crops like strawberries, tomatoes, grapes, lilies, onions, and pine trees. This notorious pathogen causes both pre-and post-harvest losses by infecting all parts of the plant and causing an estimated loss of $10 to 100 billion annually worldwide.

B. cinerea can spread from one plant to another by wind, water, or even on insects, and enters host tissue either by direct penetration or through natural openings. To assist invasion across such a diverse range of hosts, this fungus employs a multitude of strategies. One major contributing factor is the extensive genetic diversity among B. cinerea strains and their polygenic architecture, where standing genetic variation in numerous genes can collectively contribute to specific phenotypes. Additionally, B. cinerea deploys a broad range of molecular weapons, including the secretion of cell wall-degrading enzymes and toxins that break down host cell walls. The pathogen also activates diverse signalling pathways as a defence against host resistance mechanisms and produces virulence factors to infect the host. Notably, recent observations show that B. cinerea sends immune-suppressing small RNA molecules to the host, effectively silencing host genes by manipulating their RNA interference machinery possibly creating a mass confusion attack on the plant rather than a specific targeted attack.

The pathogen’s global distribution, genetic diversity, and ability to be stratospherically spread pose challenges for disease management. Farmers primarily rely on integrated strategies, combining cultural practices, chemical and biological controls, and the cultivation of tolerant/resistant varieties. Current research endeavours aim to thoroughly understand the genetic and molecular diversity of B. cinerea, aiming to formulate effective strategies to combat B. cinerea infections and mitigate their repercussions on agriculture.

On the other hand, Botrytis cinerea, otherwise known as ‘Noble Rot’, can be a favourable fungus infection, when harnessed to produce dessert style wine.

Grapes become infected and then dehydrate, resulting in a natural sugar level concentration much higher than would usually be present in normal grape ripening.

The Botrytis spores also deliver components into the grapes that change the character of the resultant wine, increasing complexity and expression beyond varietal notes into a realm reminiscent of honey, apricots and marmalade.

To produce a ‘Botrytised’ wine it takes a lot of planning and meticulous work in the vineyard. Not all grapes are suitable for wine production influenced by Botrytis cinerea. Ideally, the grapes have thin skins and grow in tight bunches. Semillon and Muscadelle for example, are ideal.


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