Protection against diseases such as root rot is one of the greatest challenges to overcome for people who grow food crops hydroponically. However, in a report published this February, it was found that corn steep liquor substantially suppressed the growth of Fusarium oxysporum f. sp. Lactucae via antifungal and biostimulatory properties. Such a discovery may offer hydroponic food-growers a simple strategy to protect their crops from root rot.
“Root rot” is a colloquial term that can describe a number of different fungal infections. Among these are fungi from the genus Fusarium—a sexually reproducing fungi that acts as a vascular pathogen in a wide variety of plants. To date over 120 different varieties of Fusarium fungi have been identified, many of which have adapted to specific plant hosts. They are ubiquitously found in soil and can survive for extended periods of time even without the presence of a host plant. Once a plant host becomes available, the fungus attacks the vascular tissues. The plant subsequently experiences stunted growth, wilts, loses leaves, and will eventually die.
Fusarium fungal infections pose a large threat to hydroponic gardeners. Hydroponically grown food is an increasingly popular cultivation strategy in which plants receive their nutrients primarily through a solution as opposed to soil. In addition to increasing efficiency and plant yields, hydroponics also offers the advantage of dramatically decreasing the risk of soil-borne pathogens. However, if a pathogen such as F. oxysporum is accidently introduced the system either through dust particles or contaminated equipment, the levels of moisture and temperature provide ideal conditions for the fungus to rapidly grow and spread throughout the hydroponic system.
In an effort to address this issue, researchers from Ibaraki University and other Japanese institutions investigated the use of corn steep liquor as an agent to protect hydroponically grown crops from root rot. Corn steep liquor (CSL) was originally developed as a fertilizer from fermented corn extract. Not only is CSL high in carbohydrates and protein, but it also is known to promote the growth of nitrogen-fixing bacteria.
To investigate whether or not CSL could also be used to inhibit root rot, researchers infected hydroponically grown lettuce plants with F. oxysporum. They then measured the subsequent growth of roots and shoots of the lettuce plants and looked for F. oxysporum growth on the plant roots and in the hydroponic liquid medium. In addition the researchers also observed the growth of F. oxysporum on plates both with and without CSL additives.
The results of this study indicate a dual-action mechanism that supports the use of CSL for the prevention of root rot in food crops. First, the CSL treatments inhibited the growth of the branching vegetative part of the fungus known as the mycelia. Previous studies into this inhibitory effect suggest that microbial fermentation may be part of the mechanism, although the details are not yet known. It is thought that perhaps some of the antioxidants, vitamins, and volatile nitrogenous or acid compounds may act separately or in combination to inhibit fungal growth.
Secondly, the Japanese researchers also noted that CSL has a biostimulatory effect on beneficial microorganisms which deter F. oxysporum growth. These include bacteria and other microorganisms that also grow in the hydroponic solution. They act by either attacking the germinating fungus as it sprouts or cause the ruptures of the mycelia cell walls.
Corn steep liquor is widely available and quite cheap. Therefore this new information that hydroponically grown food crops can be effectively and economically protected against root rot will certainly interest both the amateur and industrially sized hydroponic growers.
By Sarah Takushi