Evolution of lentil diseases over 25 years in western Canada

Lentil was first grown in Canada in 1969 and was relatively disease-free until 1978. By 1996 the crop occupied 300 000 ha annually. It is affected by three major diseases, ascochyta blight, anthracnose, and botrytis stem and pod rot. Ascochyta blight was reported in Saskatchewan in 1978; it causes major yield losses and seed discoloration, which is increased by late maturity and the practice of swathing. Horizontal spread of ascochyta blight from crop residues is limited, which is characteristic of rain-splash dispersal. Originally described as Ascochyta lentis, the pathogen is highly host specific, but morphologically indistinguishable from A. fabae, and was renamed A. fabae f. sp. lentis. A heterothallic Didymella teleomorph has been found in the USA, but not in Saskatchewan, even though both mating types are present. The pathogen population has increased in virulence since 1978 and the lentil cv. Laird, which was moderately resistant when released, is now highly susceptible. Research on fungicides has led to the registration of Bravo (chlorothalonil) as a foliar protectant and Crown (thiabendazole + carbathiin) to control seed-to-seedling transmission. Breeding for resistance is a high priority. The major source of resistance is the ICARDA lentil line ILL5588. Anthracnose caused by Colletotrichum truncatum was reported in Manitoba in 1987 as a new disease. Rapidly-developing stem lesions cause dieback, premature ripening and yield losses of up to 60%. The pathogen infects other legumes but is not highly seed-borne. Microsclerotia can be disseminated several hundred metres in dust from combine harvesters. Spraying with Bravo gives good control. Breeding for resistance is underway, but good sources of resistance have not been identified. Stem and pod rot caused by Botrytis cinerea was a minor disease, mostly in the black soil zone until the 1990s, when a series of cool, wet summers resulted in widespread dieback and high seed infection levels. Seed infection causes seedling blight, which can be controlled by seed treatment with Crown.