Wheat Stripe, Leaf, and Stem Rust Diseases

Abstract

Wheat (Triticum spp.) is one of the most strategic crops in the world. It provides raw material to the agricultural industry and it is the main source of income for many rural areas. Rust diseases are among the most important biotic factors affecting the yield and quality of wheat plants. Depending on the disease’s severity in wheat cultivation fields, the level of yield losses and quality degradation may vary, accordingly, economic losses changes. Wheat rust diseases are categorized into three groups, such as stripe (yellow) (Puccinia striiformis), stem (black) (Puccinia graminis f.sp. tritici), and leaf (brown) (Puccinia triticina) rusts. This chapter presents information on the rust symptoms, identification, and management.

1. Introduction

Wheat is one of the cool climate cereals which is one of the important mineral and energy sources and involved in the nutrition of billions of people due to its suitable nutritional value, easy storage, and processing. Because of its wide adaptation ability, it is in the first place in the world in terms of production amount as well as its cultivation area. In addition, it is also a strategic product in terms of being a raw material for the agricultural industry in the world, contributing to the economy, and being the main source of income for rural areas [1].

There are diseases in wheat that significantly reduce grain yield and grain quality. There are abiotic and biotic factors that affect wheat. Biotic factors causing disease in wheat as in other plants are fungi, bacteria, and viruses. Fungal diseases are wheat leaf diseases, wheat head diseases, and wheat root diseases. The wheat leaf diseases include wheat rust diseases, wheat septoria leaf spot, and wheat powdery mildew.

Rust diseases have been known since ancient times. Especially the ancient Romans considered cereal rust to be very important and accepted it as a punishment given by the God Robigus, and they organized Festivals and sacrificed every year so that this punishment would not be repeated [2].

There are three types of rust diseases in wheat, which are called Stripe (Yellow), Stem (Black), and Leaf (Brown) rust. These rust types got their names from the colors of the pustules they form by tearing the epidermis of the plants. Rust fungi are seen as obligate parasites in nature [2].

2. Stripe rust (Yellow rust) (Puccinia striiformis)

It is the earliest and most important rust disease of wheat. Especially in the spring months, there is an increase or decrease in the intensity of the stripe rust disease depending on the climate structure. In the case of abundant and long-term spring rains, it appears suddenly and causes significant yield and quality losses by causing diseases primarily in the leaves. It has been noted that rust diseases are observed even in the early stages with the increase in temperature [3].

Stripe rust disease infects other plants besides wheat. They can infect barley, rye, triticale, and many other related wild wheat crops. Although it is usually seen on the leaves of wheat, it can also occasionally be seen on stems and heads. It can be easily distinguished from other types of rust due to the symptoms it shows on the leaf. It occurs on the upper surface of the leaves, on the leaf sheath, on the head, and even inside the husks. The rust symptoms on the leaves cover the whole leaf and kill the leaf when the disease is severe [3].

Stripe rust disease is named after the color of the disease spores (pustules), which are like a powder of orange-yellow (golden yellow) color. Stripe rust, especially on the upper surface of the leaf, creates yellow pustules like machine stitches. Since the arrangement of these pustules resembles a line, it is also called Line Rust. Summer spores occur inside these pustules which have the form of dots arranged in rows and intra row (Figure 1) [4].

Figure 1.

Symptoms of stripe rust in wheat leaves. Photos: Dr. N. Akci.

High humidity or precipitation in the spring in wheat fields induces the occurrence of the disease. The optimum temperature for the formation and development of the disease is 10–15°C. If the host-pathogen relationship is suitable with the proper environmental conditions for the development of the disease, an epidemic occurs. In the development of the disease, the first infections occurred by urediospores, which can be carried by the wind from long distances. Because rust spores are light they can be spread around even with very little wind and can be drift to the next fields. Millions of summer spores formed from pustules are dispersed by the wind in the spring. The initial infection is initiated by very few spores and is seen in the early stages when plants are just starting to develop. After that, new spores occur every 12 to 15 days, and then every 8 to 10 days, the disease rate increases, and stripe rust disease is suddenly seen everywhere. At the end of the season, winter teliospores are formed from the same pustules. The disease is carried out on wild wheat crops on the edges of the field, which remain alive during the summer, and on the wheat planted in autumn for the winter [4].

With the increase of rust disease, the use of nutrients and water increases, as well as the photosynthesis area of the plant narrows. As a result, the amount of nutrients that will produce grains decreases. It has been determined that rust prevents normal root development and nutrient uptake in the plant to a certain extent. In addition, since rust infection causes plants to reach maturity earlier than usual, it also causes the grain filling period to be shortened thus the damage increases. The severity of the damage caused by the rust disease changes according to the development periods of the plants. Flowering and earlier periods are the most damaging period. The late period is the least damaging period. If the heads are infected with stripe rust, no matter how little rust is on the leaf, the grain yield is greatly reduced. As a result of rust infection, losses occur in the yield and quality of the grain, as well as in the quantity and quality of hay [5].

The losses due to plant deaths can be very large in more severe epidemic conditions. With the decrease in grain size and hectoliter weight, indirect effects such as a decrease in flour yield and quality and even the quality of products obtained from flour occur. Due to the fact that rust diseases slow down plant growth and reduce tillering, they cause large losses in hay yield, as well as large losses in the quality of hay in some toxic substances that occur in plants [6].

3. Leaf rust (brown rust) (Puccinia triticina)

It is usually seen on the leaves, so it is also called Leaf Rust. The orange-yellow or burnt brown color pustules are in the form of large and small dots randomly scattered on the leaf surface. Leaf rust can be seen on the upper surface of leaf. The characteristic of this rust is to form smaller pustules in one or two circles around the pustule. This symptom distinguishes brown rust from other types of rust (Figure 2) [7].

Figure 2.

Symptoms of leaf rust in wheat leaves. Photos: Dr. N. Akci.

This rust usually appears on the wheat after the stripe rust before the stem rust. In the spring, summer spores cause infection at 10–18°C and high humidity. The temperature and humidity requirements for the development of leaf rust disease have the ability to spread more easily than stem rust. Thus damage to the product can be very severe. The damage of leaf rust has recently coincided with the maturity period of wheat [8].

Leaf rust disease infects other crops besides wheat. They are barley, triticale, and many other related wild wheat crops. The disease is in the form of uredospores in temperate winter regions. In spring, spores exist on the surface of alternate hosts (Thalictrum spp. and Isopyrum spp.) leaves. Then they are carried on the leaves of the wheat by the wind and form pustules of rust. It causes significant yield losses by decreasing the number of grains, hectoliter weight, and grain quality in the head. The severity of the damage caused by the rust disease changes according to the development periods of the plants. Flowering and earlier periods are the most damaging period. The late period is the least damaging period [8].

4. Stem rust (black rust) (Puccinia graminis f.sp. tritici)

Stem rust disease is one of the oldest known diseases of wheat and it is also called stem rust because it is usually seen on the stem of the wheat. In the case of an epidemic, it can cause significant yield and quality losses in grain and hay. Stem rust is the last rust disease seen in wheat. Stem rust disease occurs in all parts of the wheat above-ground. It changes in size from 3 mm to 1 cm and is mainly seen on the stem of wheat but can also be seen on the other green parts (Figure 3) [9].

Figure 3.

(a) Symptoms of stem rust in wheat stem (b) Stem rust disease in the wheat field. Photos: Dr. N. Akci.

The dark red-brown (tile-colored) pustules may occur on the two sides of the leaf, on the stem, and the head. The pustules on the lower surface of the leaf, which are seen on both sides of the leaf, are larger than those on the upper surface. The pustules are sprinkled on the stem and leaves and are large, oval, long, and darker in color than other rust pustules. Their temperature request is higher. Stem rust disease grows well in the temperature between 20 to 25°C with a proportional humidity of over 96%. If all environmental conditions are suitable for disease development an epidemic occurs. New urediospores occur every 10–15 days. When plants mature black teliospores occur near the harvest [9].

While the pustules are dispersed in low infections, it can be seen that the pustules may merge in severe infections. The urediospores that form the pustules tear the epidermis and the plant surface takes the form of a whitish collar. These torn pieces of the epidermis are seen very clearly. Stem rust spends the winter on infected plant parts. Spores are found on the underside of the leaves of Berberis and Mahonia plants, which are alternate hosts in the spring. Then they form rust pustules on the leaves and stems of the wheat by being carried by air and wind. Spores reproduce in suitable conditions and cause great damage to the crop (Figure 4) [10].

Figure 4.

(a) Berberis plant and aeciospores on the leaves of it (b) Berberis plant at a flowering period near the wheat field. Photos: Dr. N. Akci.

Stem rust creates new races where Berberis plant is present. Thus stem rust can infect wheat varieties that were previously known to be resistant. As a result, new epidemics can occur. Stem rust reduces tillering and decreases grain weight and quality. The whole product can be lost when the appropriate conditions for the disease are formed. Crop loss can change depending on the susceptible varieties, environmental conditions, races of stem rust and it differs from year to year, from region to region [10].

5. Management of wheat rust diseases

The cultural precautions to be taken to prevent rust disease are as follows. Frequent planting should not be done because it prevents ventilation and causes an increase in humidity. Weed control should be done on time and with suitable techniques. Fertilization should be done according to the results of soil analysis. Excessive nitrogen fertilizer should not be given to the field. Activities such as irrigation that will increase the humidity of the air should be avoided [11].

It is important to control weeds and alternate host plants on time. Alternate hosts of rust diseases in the surrounding or on the field edges should be destroyed. The destruction of alternate host plants provides a decrease in the amount of inoculum which causes the first infections in rust disease. Also, the destruction of alternate host plants leads to a decrease in the number of new races that may emerge due to the limited sexual reproduction in rust disease [12].

Resistant cultivars should be used for rust disease. It is of great importance to monitor the races of rust in order to develop resistant varieties for the management of rust disease. In order to determine virulence in rust disease, it is necessary to develop monitoring and prediction warning systems which also include survey studies [13].

Taking into account the climatic conditions, the course of the disease should be monitored, especially for the stripe rust in temperature of 15–20°C and humidity of 90%. In cases where the disease progresses to the upper side of the plant, it is important to prevent the contamination of the disease, especially the flag leaf of the upper leaves. When the first stripe rust symptoms start to appear on the leaves it is recommended to spray the green parts. Spraying should be done so that the surfaces of the leaves and stems are covered with sprayed water. If the climatic conditions are suitable for the development of the disease and an epidemic is possible second spraying should be done, taking into account the effect time of the drug used [14].

With the use of genetic resistance successful progress has been made in the control of wheat stem rust disease in recent years. Resistant varieties can be preferred more reliably because they are economical and environmentally friendly.

6. Conclusion

It is known that climate change causes an increase in disease. It is difficult to predict when and where diseases will spread. With the changing ecosystem the effectiveness of biological factors changes, the distribution of pathogens is affected and the entry of new pathogens is enabled. With climate change, differences can be seen in plant-pathogen systems. Disease development is the result of factors influencing the host and pathogen.

Changes in wind direction and speed affect the spread of rust spores. Therefore, the monitoring of rust diseases is important. Care should be taken against new races, disease surveys and breed analyzes should be done, and identification of the rust races is necessary. Molecular research should be carried out in a variety of breeding studies against the aggressive/virulence of rust diseases that may occur with increasing temperature and other parameters. The pathogen forms new races and these races may overcome the resistance present in wheat cultivars. Besides the increase in the spread of rust diseases is largely due to the widespread of varieties that are susceptible. In addition to this, there may be changes in the number of fungicide applications and doses.