The sweet potato is an important global crop that produces copious amounts of sweet potato starch water (SPSW) that is difficult to dispose of in developing countries. However, SPSW is often loaded with vitamins and nutrients that can promote the growth of plant-growth promoting bacteria, such as Paenibacillus polymyxa, a non-pathogenic microbe that has a history of agricultural usage due to the variety of benefits it harbours towards plants. The microbe is capable of promoting plant growth, enhancing plant leaf quality, and protecting plants against certain diseases and pathogens.
The P. polymyxa microbes may therefore be known as biofertilizers, which are alternative fertilizers to the chemical ones that are used today. Biofertilizers may appease certain concerns towards food safety and various environmental problems. Overuse of chemical fertilizers has resulted in the increase of agricultural production costs, which may decrease if biofertilizers are more widely introduced into the industry.
Researchers in China and Australia conducted a year-long study in 2010 (to 2011) to examine the feasibility of using SPSW to grow P. polymyxa cultures and to also observe whether or not using the cultures can improve crop yield/growth of tea plants (Camellia sinensis).
P. polymyxa biofertilizer was created by combining a volume of the microbes and SPSW in a flask. Different biofertilizers were synthesized at different temperatures, acidities (pH), and were even shaken at different speeds. After the biofertilizers were created at different conditions, their concentrations of various compounds were measured (i.e. nitrogen, phosphorus, carbon, potassium, iron, magnesium, etc.). Xu et al. (2014) observed that biofertilizer production was optimal at 30 degrees Celsius, pH 7, and with a 16 hour incubation time.
The biofertilizers were applied to tea plants (C. sinensis) that were situated in tea plantations located in Hunan, China. The biofertilizers were applied to the tea plants for three seasons, and were referred to Autumn (mid-August to mid-October), Spring (mid-March to mid-April), and Summer (mid-June to mid-July) tea. For each experiment, tea bush samples were extracted on the 1st, 2nd, and 3rd weeks after biofertilizer application and weighed accordingly. Green tea extracts (GTEs) were also taken from the tea plants to determine their nutritional composition (i.e. total caffeine/polyphenols/amino acids).
Using the weights of the tea bush samples, Xu et al. (2014) observed that application of P. polymyxa biofertilizers to tea plants increased their growth by 4.7 – 21.3% in comparison to crops that were not treated with the compound (it is important to note that the percentages of increased growth vary because of the growing season and the individual tea plant studied). Additionally, tea plants treated with P. polymyxa biofertilizers contained more abundant concentrations of polyphenols and vitamins compared to crops that were not treated with it (caffeine and amino acid concentrations were not considerably different compared to untreated tea plants).
Xu et al.’s (2014) study thereby demonstrates the efficacy of using SPSW to enhance the growth of P. polymyxa biofertilizer, which can increase the crop yield and quality of tea plants. It is speculated that SPSW promotes the growth of P. polymyxa because it provides the microbes with essential nutrients (required for growth) in large quantities, including nitrogen, phosphorus, and potassium. Therefore, these nutrients can also be supplied to the tea plants, which will take up these compounds via their roots and shoots.
Furthermore, P. polymyxa biofertilizers are particularly beneficial for crop production, as they provide the tea plants with specific auxin metabolites and antibiotics, which help the plants confer a resistance to certain plant pathogens such as microbes belonging to the Aspergillus and Candida group.
From the farm to your dinner plate, the humble sweet potato harbours more potential than just being delicious and nutritious.
- Xu, S., Bai, Z., Xiao, R., and Zhuang, G. (2014). Bioconversion of wastewater from sweet potato starch production to Paenibacillus polymyxa biofertilizer for tea plants. Scientific Reports, 4, 1-7.
Renee C. has received her B.Sc. in Honours Life Sciences at McMaster University. She loves educating others about different topics in science, and has developed a passion for scientific outreach. When she’s not writing articles for Hemtecks, she’s either volunteering or checking her social media accounts every 20 minutes. Along with Tiffany (Tianhemtecks), she also facilitates the blog’s Facebook page.