Abiotic Diseases

Iron deficiency can occur on calcareous soils with high pH. Such soils are common in the West Asia and North Africa region. The deficiency generally appears at the end of a cold wet winter, when the bicarbonate ion content in the soil solution has increased. If the available iron content in the soil is moderate to high, the symptoms might disappear as the soil dries and temperatures increase in the Mediterranean environment.

Symptoms: Often the deficiency appears in patches because of variations in calcareousness in most arable soils. Symptoms appear on the younger parts of the plant, mostly on new and bud leaves, which become yellow (Fig. 45). Leaflet size is very much reduced and under severe deficiency the unfolding of upper leaves is prevented. The stem becomes slender and short.
        As the deficiency advances, it spreads to older leaves and terminal growth is completely arrested.

Control: A foliar spray of a 2% solution of ferrous sulphate at the appearance of the first symptoms of deficiency can rectify the deficiency. A second spray may be needed. Iron-containing foliar fertilizer formulations available in the market also can be used.
        Preventive measures include correction of soil pH. Application of organic matter on highly calcareous soils increases iron availability.
        Genotypic differences in susceptibility to iron deficiency have been observed in lentil germplasm, but this trait has not been exploited so far for the development of cultivars resistant to iron deficiency.

Fig. 45

Manganese deficiency is usually confined to plants growing in highly leached tropical soils or high-pH soils with a high organic matter. content. It is therefore not commonly observed in lentil in the Indian subcontinent and West Asia and North Africa.

Symptoms: Symptoms are confined to younger leaves and occur as interveinal chlorosis, often in the form of specks (Fig. 46).
        Deficiency at the time of podding may lead to discoloration, splitting and deformity of seeds.

Control: Manganese deficiency can be controlled by application of manganese sulphate (MnS0₄) to soil at 5-10 kg/ha or to foliage at 0.5-1.5 kg/ha.

Fig. 46

Manganese toxicity has been reported in lentilgrowing areas of the Central Valley, dry coast and interior of Chile. The disease is known there as 'Marea Negra', 'Rona' or 'Sereno'. It causes severe yield reduction and reduction in the quality of the produce because of the development of bluish or black discoloration on seeds.

Symptoms: The symptoms (Fig. 47) appear early in the growing season and spread over the plants as the season advances. They comprise blackish-brown spots on basal leaves, progressing to upper leaves, followed by defoliation. Analysis of leaf tissue of the diseased plants shows a tissue manganese concentration two to three times that of healthy plants. The iron content of the diseased plants also is higher than the normal concentration.

Control: Raise the soil pH to near neutral to help alleviate the problem by reducing the availability of manganese in the soil.
        If poor soil conditions have been the cause of flooding and compaction, improving aeration is likely to help.
        The ability of the plants to withstand this disorder will improve if the crop has been adequately provided with major fertilizer nutrients through carriers which are not acidic in reaction.

Fig. 47

Boron availability to plants decreases with increasing soil pH, particularly in calcareous soils. Availability also decreases under drought conditions. Hence deficiency of boron can be observed in the lentil crop in the Mediterranean region, although it is not widespread.

Symptoms: Symptoms of boron deficiency are noticeable at the terminal buds or youngest leaves, which become discolored and may even die (Fig. 48). Interveinal chlorosis might occur on mature leaves and the leaflets can become misshaped.
         At an advanced stage of deficiency the young leaves turn brown and die. The buds, flowers and pods drop, causing severe yield reduction.

Control: As a preventive measure, correct the soil pH and apply boron.
        Use a foliar spray of boron as boric acid at 0.5-2.0 kg/ha.

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Fig. 48

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