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Ascochyta blight
The disease has been reported from 15 different countries: Argentina, Australia, Canada, Chile, Cyprus, Ethiopia, Greece, India, Italy, Pakistan, Spain, Syria, Turkey, the USA and the former USSR. The disease is important in Pakistan and Canada. Yield and seed quality reduction may lead to losses in potential income of more than 70%. However, the magnitude of losses depends upon the cultivar used, the inoculum potential and prevailing weather conditions.
The disease is caused by Ascochyta lentis Bond. and Vassil., which is an imperfect fungus. It produces its spores in a flask-shaped fruiting body (pycnidium). The spores are hyaline and cylindrical, with 1, 2 and 3 septa.
The disease is both stubble and seed borne. Frequency of transmission from infected seed to seedling is low, especially when soil temperature is moderate to high. Progress of foliar blight is rapid and epidemic levels can be reached under cool and wet weather conditions because spores are disseminated by rain splashes. The fungus may remain viable in the seeds for more than 30 years. It survives for more than 3 years in infected pods and seeds at 4-5°C or under shelter outdoors, and 1-5 years at the soil surface. It loses its viability within 20 weeks at a soil depth of 16 cm.
Symptoms: All aboveground parts of the host are affected at different growth stages. Tan spots, surrounded by dark margins, are seen on the leaflets
(Fig. 10), pods (Fig. 11) and stems (Fig. 12). The center of the spot is light colored and speckled with tiny, black, fruiting bodies (pycnidia) that are characteristic of the disease (Fig. 10).
Infected leaflets drop prematurely and the tips of branches wilt, turn brown and die. The crop then has a distinctly blighted appearance.
Seeds from heavily infected plants become purplish-brown, shrivelled and greatly reduced in size, which adversely affects their quality. Severely affected seeds may have whitish patches of mycelia and tiny, black, fruiting bodies (Fig. 13).
Control: Use of clean seed is advocated. Seed treatment with fungicides such as benomyl (0.2%), chlorothalonil (0.2-0.3%) orthiabendazole (0.1-0.2%) is recommended to control the seed-borne infection.
Practice a 2-3 year crop rotation along with deep plowing to reduce soil-borne inoculum.
Foliar spray (if economically practicable) using chlorothalonil (2-3 L/ha) as single application at early bloom to early pod set provides the best protection and increases seed yield.
Use resistant varieties, several of which are now available in different parts of the world.
Rust
Rust is a widespread foliar disease of lentil. It occurs in Algeria, Argentina, Bulgaria, Canada, Chile, Cyprus, Ethiopia, Egypt, India, Iran, Italy, Morocco, Pakistan, Portugal, Nepal, Syria and Turkey. It is an economically important disease in some lentilgrowing countries such as India, Pakistan, Turkey, Ethiopia and Morocco. The disease can result in complete crop failure although yield losses on a plot basis vary from 30 to 60% depending on cultivar and disease severity.
The disease is caused by Uromyces fabae (Pers.) de Bary. It is an autoecious fungus, completing its life cycle on lentil. The disease first occurs during the flowering/early podding stage as aecia which may develop into secondary aecia or uredia. The resulting uredospores and aeciospores lead to a further disease spread in the crop season. Uredia rapidly appear a little late in the crop season followed by development of telia. The fungus survives the summer as teliospores. It is also carried with seed as a contaminant in the form of small pieces of infected plant parts. High humidity and cloudy weather with temperatures of 20-22°C favor disease development.
Symptoms: Rust starts with the formation of yellowish-white pycnidia and aecial cups on leaflets and on pods, singly or in small groups in a circular form.
Later, brown uredial pustules, oval to circular and up to I min in diameter, develop on either surface of leaflets (Fig. 14), branches, stem and pods (Fig. 15). They may coalesce to form larger pustules.
The telia, which are formed late in the season, are dark brown to black, elongated and are present mainly on branches and stem (Fig. 16).
In severe infections, the affected plant dries without forming any seeds in pods or with small shrivelled seeds. The plant has a dark brown to blackish appearance, visible in affected patches of the field or in the whole field if it is totally infected.
Control: Check seed contamination by treating seeds with a suitable fungicide.
Preventive fungicide sprays of dithane M-45 (3 L/ha) at disease initiation have proved effective in checking disease spread.
Use of resistant varieties is the best method for controlling the disease. A number of such lines are now available for use in different parts of the world.
The early sown crop in some countries is more affected by rust than the late-sown one. Therefore, adjusting the sowing date may help reduce disease occurrence and its adverse effect.
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