Photo by mconnors/morguefile.com.
Bell pepper seeds are characterized by slow germination and low uniformity. Researchers from the University of Sao Paulo in Brazil and Ohio State University (OSU) seek to change that. In a study funded by the Sao Paulo Research Foundation, Ph.D. candidate Clíssia Barboza da Silva and her colleagues at OSU began experimenting with different methods and materials for priming bell pepper seed in 2011.
Seed priming is an imbibition treatment that can shorten germination time and enhance the uniformity of various crops due to influence on the early stages of germination. Priming seeds with water alone is common practice and is effective in shortening germination time. Priming seeds with various solutions can confer other benefits. By priming with plant growth regulators, da Silva hoped to see greater development of pepper seedlings and resistance to environmental stresses such as high temperatures, drought and salinity.
"Our biggest challenge was to find seed lots of different qualities in order to test the effect of each treatment on seeds with distinct physiological potentials," notes da Silva. Within the two hybrid bell pepper cultivars they chose, the researchers found seeds with varying germination speed, length and uniformity of seedling development. The scientists have spent over two years studying three lots of cultivar AF-6 and four lots of cultivar AF-7. The seeds were conventionally grown.
The bell pepper seeds were primed with two individual substances and one combination of substances. The first two bioregulators, applied separately, were 24-epibrassinolide and gibberellic acid. A naturally occurring brassinosteroid essential in plant development, 24-epibrassinolide began appearing in agricultural research in the late 1990s due to its ability to increase seedling growth, allow plants to tolerate stress better, and promote activity of antioxidant enzymes responsible for the removal of toxic substances. Gibberellic acid, a naturally occurring plant hormone, acts as a plant regulator. It promotes cell division and cell elongation, leading to increased fruit set and crop yields.
The third priming substance da Silva used was a stimulant containing kinetin, gibberellic acid and indolebutyric acid. Kinetin, a plant hormone that promotes cell division, is often used with these two plant hormones. Indolebutyric acid is responsible for plant growth, a plant's response to its environment, and the development of plant organs such as leaves and flowers.
The researchers determined that the 24-epibrassinolide solution is the most promising treatment. The positive effects of this solution on the performance of the bell pepper seeds were numerous. According to da Silva, there were noticeable improvements in the activity of antioxidant and hydrolytic enzymes, and in seedling length and uniformity of seedling development. "Most interesting is that seed lots of lower quality showed, in some cases, behavior similar to the seeds of higher quality after the seed priming with this bioregulator," she reports.
Photo by KTNG/sxc.hu.
With the priming substance chosen, the researchers shifted their focus to evaluating application methods. They tried immersing seeds in priming solution, laying seeds between sheets of moistened paper and drum priming. In drum priming, the seeds rotate inside a metal or Plexiglas drum while the solution is injected inside. Drum priming is fast and accurate. The method's low operating costs may offer a promising alternative for the improvement of bell pepper production systems, da Silva says. With drum priming, it's possible to treat large batches of seeds for large-scale commercial distribution.
"The implementation of the 24-epibrassinolide treatment using the technique of drum priming [in a Plexiglas drum] has shown more controlled and efficient hydration of the seeds, which is difficult to achieve via conventional procedures like moistened papers or solution immersion," explains da Silva.
Drum priming also helped speed the testing process along, since the ability to process large amounts of seed allowed the researchers to execute a greater number of tests in a shorter period of time.
Now the researchers are evaluating the effects of priming with bioregulators on the activity of the detoxifying enzymes catalase, superoxide dismutase and peroxidase. They're also observing the effects of the solution on early seedling growth. Using the PAGE method (nondenaturing polyacrylamide gel electrophoresis) and standard separation and assay procedures, da Silva and her colleagues are able to evaluate the activity level of these key enzymes in the removal of toxic substances from the seeds.
In addition, they are using Seed Vigor Imaging System (SVIS) software developed by OSU to obtain information about physiological parameters related to seedling growth potential. In the SVIS system, seeds are either germinated under recommended standardized conditions for three or more days, or they are germinated following a three-plus-day accelerated aging test at high temperature and relative humidity.
After a period of six days, da Silva takes an image of the seedlings using a scanner in a special enclosure and feeds the digitized image into the computer. The computer software then analyzes and computes objective parameters, such as overall seedling length, and determines total seedling length and uniformity. After computing the measurements of individual seedlings, the software calculates the sample's seed vigor by considering individual seed development as well as sample population statistics.
Both the PAGE method and SVIS have shown promising results in verifying the effects of this seed priming treatment on parameters associated with seed vigor.
Priming bell pepper seed with bioregulators appears to provide benefits for the physiological performance of the seed that exceed those derived from priming seed with water alone. To verify the effects of priming on seed performance, da Silva intends to store the primed bell pepper seeds for 12 months before planting. The research should be complete in late 2014.
The author is a freelance writer based in Massachusetts and a monthly contributor to Growing.