Wheat (Triticum sp.
Black or stem rust
Causal organism: Puccinia graminis tritici
Symptoms: It usually appers on the wheat crop late in the season when the
temperature start rising and the crop is maturing. Symptoms are produced on
almost all aerial parts of the wheat plant but are most common on stem, leaf
sheaths and upper and lower leaf surfaces. The first symptom of rust infection is
flecking of leaves, leaf sheaths, culms and floral structures. These flecks soon
develop as oblong, reddish brown uredo-pustules, frequently merging into one
another, finally bursting to expose a mass of brown uredospores surrounded by
prominent epidermal fringes. The entire leaf blade and other affected parts will
have a brownish appearance even from a distance. Later in the season, teliospores
are produced. They are conspicuous, linear or oblong, dark brown to black, and
often merging with one another, to cause linear patches of black lesions, which
account for the name black rust. In the transitional stage, there is a mosaic of
brown and black masses of spores on the affected tissues, which dry up
prematurely. Moreover, in the case of severe infections the diseased plants are
stunted and produce small spikes and shriveled grains, or no grain at all.
Pathogen: The fungus is biotroph or obligate parasite. Black stem rust is
heteroecious full cycle rust. It requires more than one host species to complete its
life cycle. Puccinia graminis tritici is a polymorphic species, producing a
sucession of different type of spores. The uredial and telial stages occur on wheat
and the pycnial and aecial stages on the species of Berberis (Barberry) and
Mahonia, the alternate hosts. The uredospores are brown, oval shaped, thick
walled and marked with thin short spines and borne singly on stalks. The
teliospores are dark or chestnut brown, two celled, germinating by producing thin
walled, hyaline four celled promycelium (basidium).
Disease cycle: The source of inoculum for black rust comes from south, i.e.,
Nilgiri and Pulney hills. In plains of North India during summer months the
uredospores cannot survive because of the high temperatures. The possibilities of
the fungus surviving on ratoon tillers or self sown wheat plants, late and off season
wheat crops and certain grasses growing in cool areas particularly in the foot hills
of Himalayas in the North, the Nilgiris and Pulney hills in the South appear to be
great. It is believed that the fungus over summers on the wheat plants and grasses
in the hilly areas and spreads to the plains in the main wheat crop season.
Management:
Eradication of self sown wheat plants and weed hosts
Adjust time of sowing, Avoid late sowing
Grow resistant varieties like Kalyanasona, Sonalika, Choti Lerma, Lerma
Rojo, Safed lerma.
Balanced application of nitrogenous fertilizers
Seed dressing with Plantavax@0.1% followed by two sprays with the same
chemical.
Spray twice or thrice Mancozeb@0.25% or Plantavax@0.1% at 15 days
interval.
Spray Propiconazole (TILT) @ 0.1%
Yellow or stripe rust
Causal organism: Puccinia striformis
Symptoms: The disease usually appears earlier than the black rust when the
grains are formed. The uredospores appear as bright lemon yellow pustules mainly
on the leaves. But in severe infections they may be seen on leaf sheaths also. The
green color of the leaves fades in long streaks on which rows of small uredosori
appears. The sori are elongated and are arranged in linear rows between the veins
of the leaf and hence it is referred as stripe rust. In severe attack this serial
arrangement is lost and large patches become covered with crowded pustules. The
sori are mostly sub-epidermal and are remained covered by the epidermal layer and
break only at the time of crop maturity. The teliospores appear late in the season
and are also arranged in linear rows. They are compact, elongated, and black which
remain sub epidermal. Plant attacked by yellow rust generally show a poorly
developed root system.
Disease cycle: It may overwinter on volunteer wheat plants at an altitude of about
1500 to 1800 meters in the Himalayas. The uredospores germinate after a period of
dormancy and form a source of inoculum for wheat crop. Some weeds like
Agropyron semicostatum and Bromus japonicus also serve as primary source of
inoculum. Secondary infection is by wind borne uredospores.
Management
Grow resistant varieties like Lerma Rojo, Safed Lerma, Sonalika and Choti
Lerma
Spray plantavax@0.1%
Removal and destruction of weed hosts
Brown or orange or Leaf rust
Causal organism: Puccinia recondita
Symptoms: The first symptom of the disease is the appearance of minute, round,
orange spores irregularly distributed on the leaves, rarely on the leaf sheath and
stem. The spores turn brown with maturity. As the disease advances, the telial
stage may be found in the same pustule. The telia are small, oval to linear, black
and covered by the epidermis. The telia are also found on the leaf sheath. Severe
rusting of leaves causes reduction in yield.
Disease cycle: Alternate host, species of Thalictrum, helps the fungus to over
summer in other countries. The role of Thalictrum is not clear in India. In early
January, the rust gets well established in the foot hills of Himalayas and also in the
plains of Tamil Nadu and Karnataka in the South. The first build up of inoculum
takes place in the plains of Karnataka and moves northwards to Maharashtra and
Madhya Pradesh. The inoculum from the foot hills of Bihar and UP moves to the
northern plains. Therefore the brown rust appears slightly later in the Western hills
of North India. The rust population of the north and the south moves in opposite
directions, finally merging into each other, and causes serious disease in the wheat
growing states.
Management
Grow resistant varieties like Sonalika, NP 700 & 800, Lerma Rojo and Safed
Lerma.
Spray Mancozeb@0.25%
Seed dressing with Plantavax@0.1% followed by two sprays with the same
chemical
Disease cycle of wheat Rust
