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Understanding the science behind plant health

Sunlight. Air. Water. Nutrients. These fundamental elements are brought together through a complex web of processes to transform a seed into a plant and then help that plant grow to maturity.


May 1, 2009
By Top Crop Manager

Topics

Sunlight. Air. Water. Nutrients. These fundamental elements are brought together through a complex web of processes to transform a seed into a plant and then help that plant grow to maturity.

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Growers can see the difference in their crop with the use of Headline (plants on right).

 

Understanding these processes is one thing; uncovering the effect crop protection products, such as fungicides, has on these processes is another. Specifically, determining how such products impact a plant’s ability to survive and thrive is a key area of research across the agricultural chemical industry. This is because, the stronger and healthier the plant, the better its ability to withstand increasing environmental stresses to grow and produce.

From the field to the laboratory and back
Several years ago, growers using Headline fungicide from BASF noticed that plants treated with this fungicide were not only being protected from disease, but also were greener, grew more efficiently and were healthier overall compared to untreated plants.

Several years ago, growers using Headline fungicide from BASF noticed that plants treated with this fungicide were not only being protected from disease, but also were greener, grew more efficiently and were healthier overall compared to untreated plants.
 
Following initial observations, growers, retailers, agronomists, researchers and company representatives alike were faced with the real question: what caused these added benefits? As more growers brought these plant health observations to the attention of BASF, the company invested a significant research effort into explaining how Headline improved yield, beyond the benefits of wwdisease control.

Greater stored energy for growth
According to Mark Kuchuran, senior technical development specialist at BASF Canada, “Our research shows that Headline initiates a complex series of interactions within the plant, affecting growth efficiency as well as stress tolerance. Among other factors, Headline has been shown to contribute to more efficient photosynthesis and a decrease in respiration leading to a reduction in ethylene produced by the plant.”

Photosynthesis is the process in which the plant uses the energy drawn from sunlight to take in carbon dioxide and water, release oxygen and store more carbon as energy for growth.

Respiration is the opposite process to photosynthesis, which uses oxygen and carbon produced during the daytime photosynthesis to release carbon dioxide and energy.  BASF studies show that plants treated with Headline have a significant reduction in night-time respiration compared to untreated plants,  meaning that less carbon dioxide is released so more remains available to use as energy for plant growth or stored for the development of larger and more consistent seed.

Another process fundamental to plant growth is the ability of a plant to draw nitrogen from the ground. While the level of nitrogen available for uptake from the soil is an important factor, increasing the plant’s nitrogen uptake ability (or assimilation) also helps to enhance the plant’s growth. Headline has been found to improve plants’ nitrogen assimilation by activating an enzyme called nitrate reductase, which triggers the production of nitric oxide. Nitrate reductase converts nitrate to nitrite, a more usable form of nitrogen for plant growth. As a result the plant’s ability to take up and use nitrogen effectively is increased, in turn positively impacting the plant’s use of stored carbon for plant growth.

The net result of these physiological effects, BASF says, is improved growth efficiency that, depending on the type of Headline-treated crop, can result in increases in plant biomass and greener plants; bigger, more evenly sized seeds or kernels; and a greater number of seeds per pod or kernels per cob.

For grower Ryan Murray of Decker, Manitoba, the benefits are obvious: “There were a lot more pea pods per plant in the Headline-treated areas. The plant was taller and it was full of pods, and the area that wasn’t treated had maybe four to five pods per plant and shorter pods with fewer seeds per pod.”

Delayed and reduced response to stress
If a plant is stressed by disease or the elements, its energy is diverted from growing efficiently and producing seeds to simply surviving. How does this happen?

Explains agronomist Paul Sullivan, “As we move into fall, a plant begins to produce ethylene which causes it to die off. By reducing the plant’s ethylene production, the plant is able to grow right up to full maturity, providing more opportunity for it to produce longer into the season.”

The scientific explanation for this is that nitrate reductase activates the production of nitric oxide. The amount of nitric oxide produced by a plant is inversely proportional to the amount of ethylene produced by the plant, meaning the more ethylene a plant produces, the less nitric oxide is available for growth. Ethylene, a gas that promotes ripening, is produced in plant cells and leads to cell death which causes plant tissues to begin to senesce, or die off, in the course of its life cycle. Plant cells generate ethylene as part of their survival response when faced with stress.

As Kuchuran explains, “On a pea plant, for example, when a stress comes in at the flowering or reproductive stage, ethylene is produced and causes leaves to start to senesce on the bottom of the plant, so the plant has to focus on filling the pods that already exist. Our research shows that Headline decreases the amount of ethylene produced when a plant is stressed, whether through disease, drought or in hot or cool temperatures. As a result, a Headline-treated plant stays greener longer, the bottom leaves don’t drop off as quickly, and the plant can use that green material for maximum photosynthesis and carbon production, thus producing more yield.”

Increased net photosynthesis, decreased respiration, increased nitrate reductase, decreased ethylene. While researchers are gaining a deeper understanding into the specific mechanisms that explain the impact of Headline on crops, it is clear that the physiological responses within a plant are interconnected. An increase or change in one factor causes a ripple effect throughout the entire plant. In the case of Headline, these effects appear to benefit overall plant health.

Summarizes Sullivan, “Headline is a disease control product with associated benefits of providing better plant metabolic activity. There are also other benefits that become a bonus to the plant, such as allowing it to take advantage of the nutrients and moisture that are available to the crop, reducing some of the stress on the crop and allowing the plants to use their resources more efficiently.”

And for growers looking to optimize the production of every acre, anything that can be done to improve plant health is worth considering.

Is improved plant health unique to Headline?
When growers reduce a plant’s vulnerability to diseases, it will grow better and produce greater yield. The differences between the beneficial effects of fungicides become more obvious when disease is removed from the equation. Head-to-head research in the lab and in the field reveals that pyraclostrobin, the active ingredient in Headline, provides additional benefits compared to other fungicides even when there is low disease pressure.

A laboratory study of ethylene production in soybeans responding to drought stress compared other strobilurin fungicides. Direct measurements of ethylene, four hours after the induction of stress, showed a 50 percent ethylene reduction in Headline-treated plants compared to a range of 20 percent ethylene reduction to an approximate 10 percent ethylene increase in plants treated with other strobilurins. This means that plant death was most significantly slowed in the Headline-treated group.

The difference in ethylene production is even more dramatic when Headline is compared to triazoles rather than other strobilurins. At four hours after stress induction, triazole-treated plants all showed little or no impact on ethylene production in the plants.

These results support the hypothesis that the reduction in ethylene shown in Headline-treated plants is not due to a disease-inhibiting process but rather to a physiological response to Headline. Headline is actually slowing the response to stress in plants, and allowing more time for the development of yield.

Trials across a wide range of crops support these results, and comparative research continues in the field.