Plant stress and disease — threat to food security

Plant stresses and diseases caused by biotic and abiotic factors can have a significant impact on agricultural productivity.

Globally, about 20–40% of crops are lost because of pests and diseases each year. In the United States alone, invasive plant pathogens, including mushrooms, cause annual crop losses of about $21 billion.

According to the report, diseases and pests are causing wheat losses of 10.1 to 28.1 percent, rice losses of 24.6 to 40.9 percent, corn losses of 19.5 to 41.1 percent, potato losses of 8.1 to 21 percent, and soybean losses of 11 to 32.4 percent.

Plant stresses and diseases — a natural part of crop development or a deviation?

Specific deviations from the «normal» typically include only temporary changes to the standard growth model. However, many other cases include more visible changes in the structure of tissues and organs or even the loss of a typical organization. In that case, we are talking about pathological growth, which can lead to processes that disrupt the normal functioning — plant anomaly.

Regarding plant diseases, over the years, they were considered a normal part of nature and one of the many environmental factors that help maintain the balance between hundreds of thousands of living plants.

However, currently, plant pathologists define plant disease as a deviation from normal physiological functioning.

There are two factors affecting plant stress and disease — biotic (living organisms) and abiotic (non-living). Both of them have the same result — biotic factors or stressors such as pests or pathogens along with abiotic factors such as low temperature, air pollution, or nutrient deficiency may cause plant diseases.

By the deficiencies of nutrients vital for growth and development, plants can get sick — just like humans and animals. An example of nutrient lack is a change of leaf color caused by a lack of magnesium responsible for photosynthesis and energy production.

Factors affecting disease development

Humidity

High humidity (90–95%) contributes to most leaf and fruit disease development caused by fungi, water mold, and bacteria. As we know, moisture plays a crucial role in spore germination, bacterial reproduction, bacterial penetration, and infection initiation. Diseases of greenhouse crops, such as tomato mold and decay of flowers, leaves, stems, and flowering plants, are controlled by air humidity.

Image 1. Stalk rots of corn(1) and sorghum(2), corn leaf blights(3), and powdery mildew of wheat(4). Image source: badgercropdoc.com, researchgate.net, cropprotectionnetwork.org

Soil fertility

Increases or decreases in certain nutrients often affect the development of specific infectious diseases, such as stalk rots of corn and sorghum, corn leaf blights, and powdery mildew of wheat (image 1). These diseases become more devastating after the excessive use of nitrogen fertilizers. Utilizing enough fertilizer containing potassium can help in softening the issue.

Soil pH

PH soil is a measure of acidity or alkalinity. The pH scale ranges from 0 to 14, where seven is neutral. Values below 7 indicate acidic soil and above 7 — alkali. Several diseases are affected by pH soil. Clubroot, a root vegetable virus, can be controlled by increasing the pH, while common scab, potato disease, is more likely to cause problems in alkaline soils.

Image 2. Charcoal rot of corn(1), sorghum(2), potato scab(3), and white onion rot(4). Image source: cropprotectionnetwork.org, potatoesincanada.com, gardening.which.co.uk

Soil moisture

High soil moisture levels encourage the development of harmful water mold fungi. Overwatering by lowering oxygen and increasing carbon dioxide levels in the soil makes the roots vulnerable to root decomposition. On the other hand, low soil moisture is responsible for the charcoal rot of corn, sorghum, soybean, potato scab, and white onion rot (image 2).

How can it be harmful to neighboring plants?

So, we know that diseases affect plants as they affect humans. If plants do not sneeze, how diseases in plants get transmitted from one crop to the other?

1. Viruses affecting plant leaves are frequently spread by the wind.
2. However, they can also transfer to nearby plants by traveling through drops of water from rain or irrigation.
3. A high number of viruses are carried and transmitted by insects and mites — vectors of the virus. The main vectors are about 200 species of aphids carrying mainly mosaic viruses by air.
4. Plant viruses are transmitted through the soil by nematodes, as well. They can spread by spores of primitive soil-dwelling pathogenic fungi that cause large veins of lettuce, wheat mosaic, and tobacco necrosis.

Plant growth stresses and diseases detection technology

Identifying abnormal signs of growth as soon as possible and knowing how to deal effectively with the specific disease is a permanent challenge for farmers.

The faster growers respond to an issue, the more yield they are going to gain. So, for today, the best answer for optimizing output in agriculture and also minimizing the outbreaks — yield monitoring and rapid anomaly and disease monitoring applying machine learning-based anomaly detection methods.

Our R&D Team has prepared an article about SoilMate’s approach to this issue.

Well, stay tuned for the following Wednesday, and don’t miss our publication!