Abiotic Diseases

Freezing injury- is an important abiotic stress in the fall-planted lentils that face the severe winters of the Anatolian Plateau of Turkey, the USA, Canada, the former USSR and the high plateau of Algeria, and it affects winter survival of lentils grown in these areas. Temperatures of 0°C or below cause freezing injury, especially if they occur suddenly. Plants in low areas of a field, where the cold air sets in, experience more freezing injury.

Symptoms: Dead growing points of plants are the most obvious symptom of freezing injury (Fig. 36). The damage normally occurs in the early stage of crop growth, during the most severe winter conditions in January (Fig. 37); however, damage at flowering time is not uncommon.
        The frozen leaves may become roughened and leathery and develop jagged edges (Fig. 38). Death of interveinal tissue is a diagnostic symptom of frost injury.

Control: The use of cold-tolerant or winterhardy lines is the best control. The lentil lines from Turkey (Kislik-Pul 11, Kislik-Yesil 21 and Kislik-Kirmizi 51) are winterhardy as they survive exposure to air temperatures of -25°C. Four lentil germplasms have been registered as winterhardy from the USA: WH 2040, WH 8449085, WH 8449090 and WH 9449041.

Fig. 36

Fig. 37

Heat stress is often encountered during the reproductive phase of crop development, particularly in West Asia and North Africa (WANA) including Egypt and Sudan where hot days can prevail in winter. It can also occur at emergence and during seedling establishment in the Indian subcontinent and WANA. The off-season, summer planting in WANA predisposes plants to heat girdling because of high soil temperatures in contact with the stem base, caused by lack of shade.

Symptoms: Heat stress at the emergence stage adversely affects the germinating seed; the epicotyl shows yellowing and withering. Heat stress results in no emergence or severe reductions in emergence causing scanty plant stand.
        Heat damage in the summer planting causes pinching of the stem base at the soil surface, which results in yellowing and withering of plant and eventual death. Below the soil surface, the stem and root remain healthy.
        At the reproductive phase, flowering is inhibited or flowers wither, resulting in partial or complete loss of lentil seed yield.

Control: The use of lentil varieties tolerant to heat stress will be a good solution but such varieties are not yet available for commercial cultivation although some genetic variation has been noted. Cultivars from Egypt and Sudan, e.g., Giza 9 and Selaim have better heat tolerance than those from temperate regions.
        Delaying planting will reduce the damage due to heat stress at emergence and seedling growth stages in the Indian subcontinent.
        Using a high seed rate and uniform depth of sowing will produce a thick and even stand, which will reduce the chances of heat girdling of lentil seedlings in summer planting.

Fig. 38

Waterlogging in lentil is a problem mainly in the seedling stage although it may occur in the later stages of crop growth as well. It is common in fields that are unevenly levelled in all the lentil-growing areas. It adversely affects plant stand and crop yields.

Symptoms: Waterlogging occurs in low-lying patches of the field where the plants become yellow, weak and stunted. When waterlogging persists, they wither and ultimately die (Fig. 39).
        The roots and collar portion of the affected plants show rotting. On older plants, waterlogging creates bands on the portion above the collar, at the level of the water touching the plant.

Control: Proper levelling of the field should be practiced to help avoid waterlogging.
        Exercise care while flood irrigating lentils to avoid overflooding of the field.
        It would be useful to plant varieties that are waterlogging tolerant, but presently no such varieties are available. A few germplasm lines (FLIP 84-51L, 74TA264) show good tolerance to temporary waterlogging in field. These are being used for breeding tolerant cultivars.

Fig. 39

Salinity is often encountered in irrigated agriculture in areas where the water table is shallow (0.5-3 m) or the irrigation water has a high salt content (>1000 ppm). Lentil is highly sensitive to salinity and suffers from salinity stress when the electrical conductivity of the saturation extract of the soil is >4.0 mmhos/cm. Many fields in the Indian subcontinent and some in West Asia and North Africa (particularly in the Euphrates-Tigris basins and along the Nile in Egypt and Sudan) are affected by salinity. Salinity generally occurs in uneven patches in the field and there is often a gradient of salt content from low to high from the outside to the center of the patches. The severity of symptoms, therefore, shows a gradient parallel to the salinity.

Symptoms: Under excessively high salinity there is failure of germination or, if germination occurs, there is stunted growth with plants developing yellowish discoloration followed by development of bright reddish pigmentation (Fig. 40). Nodulation is poor or absent.
        When salinity develops because of the rise of water table after the crop establishment, the crop stops growing, shows moisture stress by drooping of leaves  and after a few days the plants defoliate and die.

Control: Lentil should not be grown in fields with a known history of salinity because it is one of the most salinity-sensitive crops. Salinity-tolerant cultivars are not available.
        In fields with low salinity, use ridge sowing: plant two rows of lentil on the inner sides of the ridges above the irrigation ditch.
        Improve underground drainage in areas where the salinity is caused by a rise in the water table. Avoid using brackish water for irrigation, or dilute it with fresh water.

Fig. 40

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