In this article we will discuss about the annual recurrence of wheat rust in plains of India.
In India wheat is one of the most important staple food crops and it is cultivated over 13 million hectares.
Three types of wheat rusts are known and all of them frequently occur in India.
These are:
1. Black or stem rust caused by Puccinia graminis tritici.
2. Orange – Brown rust caused by P. recondita (= syn. P. triticina)
3. Yellow stripe rust caused by P. striiformis (= syn. P. glumarum)
All the three rusts have an alternate host to complete their life cycles.
These are:
Pucciniagraminis tritici: Alternate host Berberis lycium and Berberis vulgaris.
P.recondita: Alternate host Thalictrum flavum.
P.striiformis: Alternate host Muehlengerbia hugeli.
In Indo-gangetic plains of India wheat is a winter crop. It is shown in October, November and December and is harvested in March and April. In hilly regions of Western Himalayas the wheat crop is shown in the month of September and October and harvested in April and May.
In plains, the wheat crop shows the infection of rust disease in the month of January to March. How this disease appears regularly every year on wheat plants?
This annual recurrence of rust in plains may be due to the following facts:
1. Role of Uredospore’s from Plains:
Uredospore’s are considered as the possible cause of infection. The infection of wheat rust (uredinal stage) appears in the month of January and February when the plants are one to two feet high. In plains wheat-crop is harvested in the month of March and April.
After the harvesting there is the possibility that uredospore’s may survive in the soil to infect the wheat plants next year. But it has been proved that uredospore’s cannot remain viable at 95°F temperature. The temperature in the Indo-gangetic plains even in shady places is 115°F. Therefore, there arises no question of survival of uredospore’s in the summer season in plains and they have nothing to do with the recurrence of rust.
2. Role of Barberry Plant (Alternate Host):
It was also considered that the aecidiospores produced on Barbery plant may cause the annual recurrence of the rust disease, but it was observed that eradication of Barberry bushes does not help in controlling the annual recurrence of rust disease.
Moreover, the barbery plants are usually found growing on high altitude of 3000-8000 feet, several thousand kilometers away from the crops grown in the plains. So, there are mush less chances that alternate host play any role in the recurrence of rust disease. (In the hills the alternate host plays an important role in the continuation of the life cycle as both the hosts are found near each other.)
3. Mycoplasma Theory:
According to Erichson (1894) that inside the grains a mixture of host protoplasm and fungus protoplasm is formed which is known as mycoplasma. When such seeds are sown next year, the crop shows the rust infection. However, this theory was discarded because the protoplasm of the fungus cannot remain viable at 95 °F temperature (Ward, 1905).
4. Role of Basidiospores:
Basidiospores can infect wheat plants but the experiments show that the spores are totally incapable of infecting wheat and they grow only on Barberry leaves and flowers.
5. In 1933, late professor K. C. Mehta worked on the problem of annual recurrence of rust in India and solved the mystery. He proved that the uredospore’s produced on the hills are responsible for the annual recurrence of rust disease in the plains of India. According to him:
(a) Uredospore’s can survive in the summer in hills (at higher altitude of 1300-2500 metres).
(b) They survive on self sown wheat plants and tillers. The atmospheric conditions on high altitude and the low temperature help for the survival of uredospore’s.
(c) In the hills the wheat crop is sown in September and October, its gets infected very soon whereas in the p’.j -.s of India the wheat crop is sown in the months of October and November. At that time the hilly crop is already heavily infected by rust disease. The wheat plants are infected by the uredospore’s survived during the summer season in hills (Fig. 10).
Recurrence of Wheat Rusts in Plains of India
(d) These uredospore’s are easily carried away by wind and first infect wheat crop in January and February. Thus, he concluded that uredospore’s produced on the hilly crops particularly in the region of Himalayas, Nepal hills for northern plains and Nilgiri.
Palni hills and Panchgani of Western Ghats for the southern plains are the causal organisms for the annual recurrence of the rust disease in the plains of India. He also suggested that the rust severity in the plains can be reduced if there is no wheat cultivation on the hills for some time.
Control Measures of Rust Disease:
(1) Cultivation of Resistant Varieties:
It is one of the most effective and practical methods to control the rusts of wheat. Some varieties of wheat like N. P. 120, N. P. 52, N. P. 4, N. P. 165 Pb., C. 591 showed good tolerance to rusts Sonara 64 and Lerema Rojo are highly resistant to black rust.
(2) Mixed Cropping:
In this method the mixed crop of barley and wheat is grown in the field. This method gives a good crop insurance even if the main crop fails.
(3) Eradication of Barberry Bushes:
The eradication of barberry plants may control the disease by cutting down the life cycle of fungus. It is the most effective method in those countries (e.g., U. S. A.) where the pathogen completes its life cycle on alternate host (heteroecious).
However, in India the source of primary infection (uredospore’s) lives in the hills and in plains it is brought through winds. Here this method is of no except one way that the absence of barberry bushes will exclude the chances of dikaryotization and new genetic varieties of the fungus.
(4) Effect of Fertilizers:
Higher dose of the nitrogenous fertilizers makes the crop more susceptible to rusts. The potassium has the opposite effect. Reduction of N in the proportion of NPK ratio helps in reducing the incidence of rust in a susceptible variety.
(5) Rotation of Crops:
This method is used on hills. In this method the cultivation of barley and wheat plant is replaced by oat.
(6) Chemical Control:
Spraying of sulphur (13-6 kg. per acre) over young healthy wheat plants, checks the rust infection to a great extent. Four to five applications of Nabam and Zinc sulphate gave efficient control of wheat rusts. Chemicals such as Actidion, Parzate, dithane liquid plus zinc sulphate, plantavax and RH-124 have given quite encouraging results to control wheat rusts.