Pests & Diseases

February 2023 Pests & Diseases

Image from Twitter

Bananas: Expiration Date in Sight

Writing in the Laidback Gardener, biologist Audrey Martel warns of the demise of the Cavendish banana. She notes that artificial banana flavour tastes unlike the bananas we eat today because it was modelled on a variety that has now almost disappeared, the Gros Michel banana from Martinique. Sugars in the Gros Michel were so intense they formed a honey-like syrup. Today’s Cavendish banana was developed by William Cavendish and Joseph Paxton in 1835. Wild bananas, of which there are about 200 species, are often inedible, containing many hard seeds and very little flesh. Wild bananas reproduce sexually, which means more genetic mixing and diversity. The Cavendish banana is reproduced by cloning so each plant is an exact genetic replica of every other plant. This lack of genetic diversity was good for stability of what became an important agricultural crop, but bad in terms of that crop’s resilience to pests and diseases. At the end of the 20th century, the fungus Fusarium oxysporum attacked Gros Michel bananas, killing almost all the banana trees. A few crops in isolated areas were saved, but the Cavendish, more resistant to the fungus, replaced it in world production. Now, however, another strain of Fusarium called TR4 that can kill many varieties, including the Cavendish, is spreading to more and more countries. In many places bananas are a staple crop, so this fungus is a threat to food security as well as livelihoods. A team of scientists has found that exposing plants to another variant of Fusarium provides protection for up to 10 days, but this solution may not be commercially viable, or permanent. We may have to go back to wild variants to breed a new banana.

Researchers from AU Flakkebjerg have studied how plants can keep pests, diseases and fungi at bay by secreting certain substances. This could be used as a plant defense of the future. Credit: Enoch Narh Kudjordjie.

Plant protection of the future may come from the plants themselves

In happier news, researchers from AU Flakkebjerg, Denmark, have studied how plants with different resistance traits interact with their microbes to respond to pathogen attack. The research is published in the journal Microbiology Spectrum. To begin with, the researchers infected two-week-old Arabidopsis genotypes growing in field soil in a greenhouse with the fungal pathogen Fusarium oxysporum, the same culprit that threatens bananas. Then they studied the results. Enoch Kudjordjie explains, “… we were absolutely sure that the plants were actually infected. The qPCR test showed a clear difference between the two genotypes, with the resistant genotype having a much lower level of the pathogen than the susceptible one.” They then continued to explore the differences between the chemistry and microbiomes in the two genotypes, and found large differences. The plant metabolites and hormones studied were distinct in both the healthy and diseased plants, confirming the involvement of certain plant chemical molecules in mediating plant defense. Likewise, they found that microbial composition, as well as microbial community networks, were distinct in healthy and diseased resistant and susceptible plants. Moreover, beneficial bacteria such as the genera Pseudomonas and Rhizobium were mostly enriched in the rhizosphere of infected plants, suggesting an active recruitment of microbes to resist pathogen invasion. This work has deepened our understanding of how plants defend themselves against a fungal pathogen. More importantly, we found a strong and unique association between individual defense metabolites and specific microbes in the healthy and diseased plants of the different genotypes. “These results strongly confirmed that three underlying host components (genes, metabolites and microbiomes), interactively control the plant defense,” explains Kudjordjie. They also suggest a future where plants are cultivated with optimized yield and other agronomic and economic gains without the use of synthetic chemicals.

Mosaic Diseases Caused by Potyviruses. Image from University of California.

Copying nature to help plants resist viruses

CRISPR gene editing is opening up exciting new frontiers in crop research. The CRISPR-Cas9 technique makes it possible to modify a region of the plant’s DNA in a targeted and precise manner, allowing desirable traits, such as disease resistance, to be retained while eliminating undesirable traits. An iterative gene-editing strategy was recently studied to help tomatoes develop better resistance to a several plant viruses. The findings are published in the Plant Biotechnology Journal.

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