Asst. Proff . Jasim Mahmod Abed

College of Agriculture – Plant Protection

Rust diseases represent the most economically significant fungal diseases in wheat and other cereal crops worldwide, and they are widely distributed across wheat growing regions. With the capacity to form new strains of fungus, rusts can attack even previously resistant varieties. Rust diseases possess the ability to spread and travel long distances by dispersal of windborne spores and can rapidly develop under optimal weather conditions .The three rust diseases affecting wheat are leaf caused by Puccinia.triticina  , stem (P.graminis) and stripe rust(P. striiformis). Leaf rust is the most common of the three diseases in the Central Great Plains and other wheat-growing regions in the United States. In some states, leaf rust disease occurs every year. Temperature plays an important role in the occurrence and development of infection, and each type of rust has a preferred temperature. Leaf rust is suitable for temperatures from 18 to 22 ° C, stem rust is suitable for temperatures from 25 to 35 ° C, and yellow rust is suitable for temperatures from 10 to 15 ° C ± 2 C. The wide difference between day and night temperature plays a major role in the occurrence of yellow rust infection, especially in the case of the availability of the maximum degrees of occurrence and development of yellow rust infection, which range between 23-25 ??C.   High levels of disease before or during flowering usually have the greatest impact on yield. Rust causes losses by reducing the number of kernels per head and the size of the kernels, and by lowering test weight and the protein content of the grain. In the case of stem rust, additional losses may result from girdling of the stems which cause plants to lodge. However, for years, the widespread use of rust-resistant varieties has substantially reduced losses caused by leaf, stripe and stem rust Rust disease is most harmful to late-maturing cultivars in years when cool, wet weather persists for an extended period of time. The fungi that cause diseases such as black stem rust, leaf rust to orange and yellow rust have many physiological strains that have been identified through their reactions to a fixed group of wheat cultivars known as differential varieties. A system has been developed to track hundreds of strains. Any genotyped variety of wheat may be resistant or tolerant to one type of rust pathogen, but no cultivar is resistant to all three rust pathogens. Every few years, new strains of this fungus appear, causing infection of previously resistant species. The life span of the stainless variety usually ranges from 2 to 4 years .New secondary families contributed to the creation of new genetic strains of this fungus, including the bonicam plant, which entered about three years ago as a new forage crop. In the epidemiological speed of the disease on most of the cultivated varieties, as well as the abatement of the blueberry as a new forage crop, which is one of the new secondary families, which can contribute to the spread of the fungus in an epidemic manner in the areas of wheat cultivation and the occurrence of severe losses. Fungi that cause rust diseases with long life cycle and dichotomous hosts are characterized by the formation of five instars and five types of spores are: The telial stage (Teliospore), the basidial stage (Basidiospore), the pycnial stage (pycniospre), the Aecial stage (Aeciospore), and the Uredial stage (Urediospore)                                                        

The most important technical recommendations to prevent the recurrence and spread of the disease in an epidemic

1- Cultivation of resistant varieties that are stable for a long time under field conditions

2- Also, the varieties must always be changed, and the age of the varieties for the farmer should not exceed five years, and to be replaced by new ones constantly in order to overcome the most virulent and pathogenic physiological strains that break the resistance genes.

3- Mixing the cultivated varieties is an effective measure in controlling the disease

4- Searching for sources of new resistance genes and introducing them into the wheat breeding program in cooperation with international bodies and interested international centers5- In light of the climatic changes and the severity of the infection, it is preferable to exclude most of the varieties that had the infection and replace them with resistant strains and varieties.

6- The use of specialized anti-rust pesticides registered and recommended by the Ministry of Agriculture in the event of an outbreak of the disease and its spread to limit its spread and the development of infection to reduce losses to the lowest possible level. Spraying with the recommended pesticides must be carried out quickly to prevent the spread of the disease.

7- Avoid the cultivation of new plant families, which can contribute as new secondary families to the creation and new genetic strains of this fungus, such as the Bonecam, as well as the Bluebanic plant, which are new secondary families.

8- Use early warning devices from the relevant research authorities and educate farmers about the necessity of periodic inspection of wheat fields, reporting injuries and spraying them immediately.

9- Chemical control using one of the specialized pesticides