Didymella rabiei (chick pea blight)

Symptoms can occur on all aerial parts of the plant and disease in the field is often seen as patches of dead blighted plants (Chen et al., 2011). Circular, initially dark-brown, necrotic lesions appear on leaflets extending to a general blighting of the foliage under cool wet conditions. Older lesions develop a grey centre in which dark pynidia of the pathogen may be seen, often arranged in concentric rings in older lesions. Lesions on petioles and stems are elongated or oval; they frequently girdle the stem causing a wilting and dieback of distal regions of leaves and stems. Basal stem lesions can cause rapid death of the whole plant. Stems often break after girdling by the pathogen. Lesions on pods are circular with a pale centre developing concentric rings of pycnidia and infected seeds show discoloured patches.

Current control of the disease is primarily through the use of partially resistant varieties coupled with the use of cultural control techniques such as rotation or deep ploughing to remove crop residues as a source of inoculum (Wise et al., 2009). Seed applied fungicides can be used to eradicate seedborne inoculum. The use of disease resistant cultivars is preferable (Singh et al., 1981; Chen et al., 2004), but resistance is incomplete and the variability of the pathogen makes resistance unreliable in many areas. Combining partial resistance with the application of fungicides such as chlorothalonil and strobilurins has been advocated (Reddy and Singh, 1990a; Banniza et al., 2011). Much effort has been put into screening and breeding chickpea cultivars with adequate resistance. Because of the major influence of environmental conditions on the disease, the standardization of screening methods is particularly important (Haware et al., 1995). The use of blight resistance in the ICARDA chickpea improvement programme has been reviewed by Singh and Reddy (1996). An integrated approach to control combining phytosanitary measures and seed-applied fungicides to reduce inoculum pressure, with partial resistance to the disease is generally recommended (Kaiser and Hannan, 1988; Chen et al., 2011).

As outlined in Biology and Ecology the disease is endemic in many West Asian and North African countries and under the cool wet conditions which often occur during the main growth period of winter sown Kabuli chickpeas, damaging epidemics occur which can virtually wipe out susceptible varieties. Actual losses incurred at any one time depend on the prevailing weather conditions, the relative susceptibility of the variety grown to the local pathogen population and inoculum pressure; a figure for overall losses across the regions where the diseases is endemic is difficult to estimate (Saxena and Singh, 1984; Reddy and Singh, 1990b).