Root rot of irrigated lentils in Iran

In some areas of Iran, root rot of irrigated lentils (Lens culinaris) was a serious problem resulting in high plant mortality and decreased yields. Pythium ultimum was the predominant soil-borne pathogen isolated from discolored, necrotic roots of diseased plants in furrow-irrigated fields at Karaj, and appeared to be the primary incitant of root rot of irrigated lentils at several other locations in the country. Pythium aphanidermatum was the primary pathogen isolated from roots of diseased lentils at two irrigated sites in southern Iran. Isolates of P. ultimum and P. aphanidermatum were highly pathogenic on roots of lentil in greenhouse inoculation studies. Other fungi isolated from diseased lentil roots less frequently were Rhizoctonia solani, Phytophthora sp., Macrophomina phaseolina, Fusarium oxysporum, F. roseum, and F. solani. Cultures of R. solani, Phytophthora sp., and M. phaseolina were less pathogenic on lentil roots than either Pythium sp., whereas the three Fusarium spp. were nonpathogens. Incidence and severity of root rot increased in Karaj field trials in treatments receiving N and P fertilizer and irrigation every 6 days. In greenhouse tests, incidence of root rot increased when naturally infested Karaj soils were amended with 1 or 10% cow manure before planting. Sources of resistance to the lentil root rot complex were found in germplasm screened in naturally infested soils at Karaj.