Increasing plant Brix levels increase plant immunity to Pythium, Fusarium, Rhizoctonia, Phytophthora, and other root-borne pathogens in aquaponics, hydroponic, and soil-based agricultural systems. Increasing Brix is also essential for improving the over quality of fruits and vegetables, productivity of the system, and working towards the goal of making food become medicine. Often this is something hobbyists and commercial growers either know nothing about, or they try to chase these in their farming systems with some to limited success. Today we will discuss the basics behind increasing Brix and plant immunity to root-borne fungal pathogens and how photosynthesis drives these processes.

Brix is a measure of the concentration of sugars that are in the plant sap. Sugars in the plant are produced through photosynthesis and are an essential part of the biological functions of the plant and the plant’s internal and external microbiome. Sugar can be thought of as a currency between plants and microbes; the plants take in the light, CO2, and water, and create glucose and oxygen. Plants then trade these carbohydrate sugars to microbes in exchange for minerals.

The 24- cycle

Photosynthesis can also be thought of as the start of carbohydrate synthesis. During the beginning and throughout the peak of the day, glucose initially is created in the chloroplast. Next, the glucose is immediately converted into energy for the plant by the mitochondria, or they are stacked together, forming increasing chains of sugar molecules that create saccharides, disaccharides, and polysaccharides.

Carbohydrates are stored in the leaves as starches or used for cellulose production. After the peak of the day, as the sun is beginning to set, the plant begins to transport these sugars down through the phloem and store them as starches in the roots.

At night the plant undergoes respiration, and it is during this period (roughly 3- 8 am or just after dawn) that the plant undergoes 80% of its growth and uses a large portion of the sugars it stored from the day.

Every day this process is repeated, when the plant has the right environment and minerals nutrition, it can produce high-quality starches really efficiently, and an increasing reservoir of these starches start to build up in the plant roots and the soil or water. During the transport period, the plant sends what it can into the roots. Still, when the roots become packed full, then fewer sugars are transported to the roots, which results in polysaccharides begin to increase in the leaves these which results in a higher overall Brix reading.

Environmental effects on carbohydrate synthesis 

Several environmental factors play a role in carbohydrate synthesis, including water and air temperature, humidity, CO2 levels, O2 levels in soil or water, light, air movement, other crops, plant debris. If these parameters are not ideal for the plant, the plant will be stressed. The effects of the stress are not always visual and can result in decreased production and increase disease and pest susceptibility.

We use Vapor Pressure Deficit (VPD) to determine our ideal air temperature and relative humidity ranges based on the crop, life stage, and the ambient environment, which we have to work with. On a home scale, we track some of our environmental parameters using a wireless sensor.

Once the environment is cleaned and in proper ranges for your crops, then you can move on to the management of minerals.

Mineral effect on carbohydrate synthesis

Carbohydrate synthesis can be increased by increasing the quantity of chloroplast, and the density of chlorophyll within the chloroplast since these are key to photosynthesis. The primary minerals responsible for this are Magnesium, Nitrogen, Iron, Manganese, Phosphorus, and various micronutrients (Cobalt, Selenium, Zinc, Copper, Boron, Molybdenum, etc.) which act as an enzyme cofactors.

For the management of mineral availability, there are many solutions. We recommend beginning by adding magnesium sulfate (Epsom salt) at the rates suggested in Table 1. You should be able to see Iron and Phosphorus deficiencies in the plant if you have them, and you can add these using AquaIron or AquaDown. Deep green veins with yellowing interveinal tissue indicate and iron deficiency (Figure 1). Deep purple colors and abnormal growth and tissue formation indicate a phosphorus deficiency (Figure 2).  For micro-nutrients, I recommend a foliar spray of Sea-90  at the manufacture recommended rates; You can learn more about this on our salt addition blog. Maxicrop and Cytoplus are also excellent products that use micronutrients from seaweed.
To reduce stress caused by environmental factors above, you can add a small amount of sugar to this foliar spray or mixture to help make up for the glucose the plant couldn’t make during the day.
Depending on the crop and stage of life, additional magnesium, calcium, or potassium may also be needed. During vegetation, magnesium and calcium are essential as calcium is responsible for cell division, and magnesium is required to create chlorophyll (among other things). Right before flower and fruit development, the plant needs a decrease in magnesium since fewer leaves are growing and an increase of calcium. It is crucial calcium is available at adequate levels until the cell expansion phase of the fruit has finished. Once the fruit has completed the cell expansion phase, then calcium should be reduced, and potassium increased; these can be added to the water using  Aqua-Up or applied as foliar sprays.
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Table 1: General Recommendations of Magnesium Sulfate Additions per 3-4 weeks *This is based on hydroponic standards and does not account for the magnesium in the fish feed

Brix and Human Health

A few things we can gather from increasing Brix are:

  1. Increasing Brix means increasing the quality of the sugars
  2. Increasing Brix means increasing biologically available minerals like calcium, and micronutrients which are often limiting in our diet
  3. Increasing Brix means increasing taste
  4. More taste means more secondary metabolites which have numerous medicinal properties in them

I am no doctor, but I can see already why increasing Brix can improve our health. To further this research, the Bionutrient Food Association is working on a great project to make testing of secondary metabolites cheap and readily available, helping push the conversation from growing food to growing medicine.

Carbohydrate source and effect on root-borne pathogens

Many root-borne pathogens affect plants. A few common pathogenic fungi include Fusarium spp. Rhizoctonia spp. Pathogenic oomycetes include Pythium spp. And Phytothophroa spp. Many species exist within these genera with various niches they have established in their environment, some of which play a symbiotic role, others that do not.

Instead of thinking of pathogens of “bad guys,” we should begin to think about them as decomposers; their role in nature is to remove plants that are unhealthy. Most of the time, our plants have to deal with the environmental issues and lack of minerals to achieve their maximum photosynthetic potential.

When plants can photosynthesize at their maximum potential, then they can develop complex sugars. Many oomycetes are unable to breakdown complex polysaccharides like cellulose, pentose, pectin, or starches. Therefore, when the plant can build these, they create a natural resistance.

The fungi are more developed and have the enzymes to break down the complex carbohydrates. However, when the plant has more complex carbohydrates, then the fungi will take longer to penetrate the plant cells unless it attacks newly developed cells. In addition to creating this barrier of complex sugars around the leaves and roots by supplying adequate nutrition, we have provided the plant with minerals like calcium, copper, boron, and zinc. These nutrients naturally help suppress pathogenic fungi; other beneficial nutrients that play a role in this in this include silicon, selenium, and cadmium.

Measuring Brix 

Brix is measured with a refractometer; these are used for several applications, including testing salinity, Brix, pharmaceuticals, and various chemicals. There are digital and analog meters. It is important when choosing a meter to make sure that the one you pick is meant for measuring Brix as they are not all calibrated the same way.

Rather than trying to replicate already well-published material, here are the steps and processes for measuring Brix in several crops, including cucumbers, leafy greens, tomatoes, sweet corn, and watermelon.