The Algae-rithm of Sustainable Agriculture: Can Algae Replace Harmful Pesticides and Fertilizers?

September 27, 2023

Davis, CA

As the world’s population continues to grow, it is critical that we increase our food supply.

While agricultural products are always subject to the threat of pests and pathogens, climate change and mono-cultivation are exacerbating their adverse effects.³ Many crops are currently grown with pesticides and fertilizers to maximize production, yet these applications are harmful to human and other life. More sustainable solutions are urgently needed. Fortunately, several exciting and commercially viable pesticide alternatives are available and being explored, including microalgae, the subject of my research as a Microbiology PhD student at the University of California, Davis.

As a pesticide alternative, microalgae hold a number of advantages. They are easy and cheap to grow and microalgal products are less harmful than current synthetic pesticides and fertilizers. Because algae are photosynthetic and make sugars using sunlight, they can grow in low-nutrient water sources, such as seawater.⁴ One type of microalgae is cyanobacteria. Cyanobacteria were the first photosynthetic organisms and made the atmospheric oxygen that we breathe today.⁵ Cyanobacterial extracts can act as plant “biostimulants”, increasing plant growth, stress tolerance, or nutrient absorption. For example, several cyanobacterial species can turn nitrogen into a form that plants can use, maki

ng nitrogen available to plants without the application of synthetic fertilizers.⁷

Spirulina is a type of cyanobacteria. These bacteria can be dried and crushed into a vibrant blue-green edible powder. Spirulina’s culinary origins date back centuries when it was a dietary staple for Aztecs in pre-colonial Mexico.⁸ It is considered a superfood due to its high protein content and nutritional value as a source of vitamins (e.g. thiamin and riboflavin) and minerals (iron and manganese).⁹ Spirulina extracts can also increase activity of beneficial microbes. For example, in biodiesel-contaminated soil, soil microbes degrade the diesel faster when spirulina extract is added.¹⁰

This spirulina extract can be easily dissolved and applied directly to soil.

One such extract is derived from spirulina and is intended for use in agriculture. The extract improves the growth of several crops, including tomato, bell pepper, lettuce, basil, and strawberry.^11,12 The extract also increases plant growth in diesel-contaminated soil and expands the lifespan of lettuce watered with polluted river water.^13,14 This extract shows great promise as an environmentally friendly fertilizer replacement (see images below). Can it also help replace pesticides? My research seeks to answer this question, based on our knowledge that when a microbe stimulates plant growth, it often triggers the plant to produce both growth and disease-fighting defensive hormones.¹⁵

Strawberry plants were grown with spirulina (left) vs without (right). The plants grown with spirulina grew bigger and suffered fewer symptoms of nutrient deprivation than the ones grown without, such as reddening foliage.

A portion of my PhD research involves testing whether the spirulina extract protects strawberry plants against disease. Currently, strawberries are among the “dirtiest” produce, with residues from more pesticides found on these fruits than on any other fruit or vegetable.¹⁷ Common pesticides include cancer-causing chloropicrin and ozone-degrading methyl bromide, and most pesticides end up in the soil or drain into waterways, damaging soil microbes and contaminating bodies of water. Unfortunately, the strawberry industry lacks effective and affordable alternatives for pest and pathogen management.¹⁸ Spirulina extract increases the growth of strawberry plants, but it is unknown whether it also protects strawberry plants against disease. I expect that my research will reveal that spirulina can be useful for preventing plant disease while boosting plant growth and that spirulina extract can help reduce reliance on both pesticides and fertilizers.

I am a Microbiology PhD student at the University of California, Davis. My research involves using microbes, like spirulina, to protect plants against diseases and stressful growth conditions, such as high salinity. I would like to thank the Foundation for Food and Agriculture Research, UC Davis, and Dr. Johan Leveau for their support and for providing me with such great opportunities. I am excited to contribute to research and innovation in sustainable agriculture.

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