Powdery mildew of wheat

Powdery mildew of wheat

Pathogen:- Erysiphe graminis.

Systematic position of pathogen:- Class- ascomycetes; order-erysiphales; family-erysiphaceae.

Distribution:- The powdery mildew of wheat is commonly found in those regions where there is enough of moisture during sowing time. This disease has not or little important in the plains of India. This disease is commonly found in lower hilly tracts of northern India. This is a common disease of wheat in the terai regions of the Uttar Pradesh and Bihar. The disease has been frequently observed in Dehradun district of Uttrakhand.

Symptoms :- The pathogen  is an obligate parasite, and usually found on leaves, young shoots, and other young tissues of the host plant. In the beginning it appear as superficial flocculent growth on the upper surface of the leaves, which later on spreads to  sheath and floral bracts. The fungus may appear in an isolated white patch, in the beginning, which may coalesce with other patches and form big one on the leaves .Sometimes, whole leaf is found to be affected. The mycelium on the host is entirely superficial, forming a flocculent matted growth, at first white when the conidia are being found, thereafter changing into a grey or reddish-brown color when cleistothecia are developed. In severe cases, the leaves become crinkled, twisted or variously deformed .The top of the shoot droops down and withers and ear development is checked to some extent. Later on, usually at earning time, Small, dot-like ,dark ,are formed in the superficial mycelia weft.                                                                                                            From much discoloration and coverage of the host epidermis by the fungus, photosynthesis is less and there is much chlorosis, which makes the plant weak. The development of the infected ears is arrested and the ears is arrested and the ears wither. If the disease incidence takes place at the milk stage, the grains are dried and shriveled.

The pathogen:- the disease is caused by Erysiphe graminis var. tritici. This is an obligate parasite. The mycelium is ectophytic and consists of sparingly branched, thick-walled hyphae, 4 to 5 micron wide, which are interlaced into a web, covering a greater or less extent of leaf and stem. If forms a white, web-like coating over the leaf and sends haustoria into the epidermal cells of the host. Usually the haustorium is branched, forming finger-like processes, and frequently provided with an external disc or appressorium, from which the haustorium proper arises and pushes into the epidermal cell. As a rule, the fungus does not penetrate deeper in the tissue

Nature abd recurrence of disease:- the recurrence of the disease takes place through the cleistothecia,(the penetrating body) .The cleistothecia penetrate on the straw and plant debris after harvest, and provide the necessary inoculums for  the next season. The primary infection is brought by ascospores, and the secondary infection is from the air-borne conidia.

Control measure:-

Resistant varieties- the best method of control is to sown resistant varieties, in countries, like U.K, and Canada, much work has been done to evolve the resistant varieties. In India too, there are some progress in this direction. Varieties NP 710, NP 718, E 720, are moderately resistant; sharbati sonara, Sonora 64, and chhoti larma are recommended for cool climate regions of northern India; HD-1980 and HD 2204 are also resistant. Recently developed varieties, such as HB 208, CPAN 1676, VL 401 and HD 2074 are found resistant against all races of E. graminis tritici.

Chemical control- Sulphur dusting has been proved to be fruitful in the control of this diseases. But the cost of treatment is prohibitive and the control is not practical. Fungicidal sprays proved effective in control of this disease. Spray with systemic fungicide, benlate(0.1%) gave good results. Spray of calixin is equally effective. Karathane (0.1%) is also effective. Control to some extent can also be achieved woth ethirimol and dimethirimol, used on soil drench. Seed treatment with bayleton (0.1-0.2 %) or its spray on leaves (100-500 microgram in ml) gave good results.