Pathogen Profile #6

Hello Robigalia Reader and welcome back to another week of Robigalia, delivering the latest in plant pathology directly to your inboxes. This week we’re diving into Black Rot of Crucifers!

While it might sounds like the title of a new pirate film, black rot of crucifers is a serious bacterial disease that affects cabbage, broccoli, cauliflower, and other vegetables from the cabbage family (crucifers). It is caused by the bacteria Xanthomonas campestris pv. campestris and this disease can severely damage crops and cause yield losses of up to 40%. First described in Kentucky, USA in 1894, the disease is now widespread throughout the world.

The first signs of black rot are V-shaped yellow patches appearing at the edges of leaves, with the point of the 'V' pointing inwards. As the disease progresses, the veins in the affected areas turn black, and the leaves wilt, turn brown, and drop off the plant. Cutting open the head or stem you'll see the internal vascular tissues are blackened and decayed. The bacteria can spread throughout the plant, blocking water and nutrient flow which stunts growth and can cause head rot in crops like cabbage.

Black rot is primarily seed-borne but can also spread through infected transplants, rain splash, irrigation water, and contaminated equipment. The bacterium thrives in warm and humid conditions, making it a persistent threat in suitable climates. The disease can survive for up to 2 years on old crop debris or cruciferous weeds in the field. Insects, tools, and workers moving between wet plants also aid in spreading the bacteria.

Prevention is key, as there is no cure once plants are infected, with contaminated seed the greatest source of pathogen spread. Good sanitation, crop rotation, and using disease-free planting material are the most effective ways to manage this devastating disease. Thankfully, disease resistant and tolerant plants have been developed, such as 'Guardian', 'Defender', and 'Gladiator' for cabbage, and 'Arcadia' and 'Eureka' for broccoli.

While black rot remains a significant challenge for brassica growers globally, a combination of genetic resistance, cultural practices, and chemical treatments, it is possible to manage and mitigate the impact of this destructive disease. Ongoing research and advancements in molecular biology continue to provide new insights and tools for effective disease control.

If you’re interested in diving into the science about black rot, I’ve summarised a few articles below.

Xanthomonas campestris pv. campestris papers

Virulence Factors Assessment for Some Xanthomonas campestris Strains Causing Black Rot in Cabbage

• Researchers have found that increased production of lipopolysaccharides, adenosine kinase, cell adhesion, and xanthan gum correlates with higher virulence. These insights are crucial for developing effective management strategies for black rot in cabbage.

Molecular Marker Development for the Rapid Differentiation of Black Rot Causing Xanthomonas campestris pv. campestris Race 7

• Researchers have developed new molecular markers to quickly and accurately identify race 7 of the bacterium Xanthomonas campestris pv. campestris. These markers enable rapid detection through PCR, offering a more efficient alternative to traditional methods, and can help improve disease management and breeding programs.

Assessing the efficacy of phyllospheric growth-promoting and antagonistic bacteria for management of black rot disease of cauliflower incited by Xanthomonas campestris pv. campestris

• This study investigates the use of phyllospheric bacteria as biocontrol agents against black rot disease in cauliflower. The research identified four promising bacterial strains, including Pseudomonas fluorescens CFLB-27, which showed significant disease suppression and plant growth-promoting traits, offering a sustainable alternative to chemical pesticides.

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Until next week,

Alyssa