Responses of Red Clover Cultivars to Stemphylium Leaf Spot

Abstract

Stemphylium leaf spot, caused by Stemphylium sarciniforme (Cav.) Wiltsh., occurs on red clover (Trifolium pratense L.) at high severity levels in the northeastern USA and Canada during most seasons. Information on genetic variability for resistance to the disease and the effect of the disease on forage yield of red clover is lacking. The objectives of this research were to assess the levels of Stemphylium leaf spot on cultivars of red clover and to determine the impact of the disease on forage yield. Red clover was grown in the greenhouse and inoculated with S. sarciniforme to determine the levels of resistance within and among cultivars and to ascertain the degree of dry matter yield losses caused by this disease. Significant differences in leaf spot size severity scores occurred among 15 cultivars, but even the most resistant cultivars were scored as susceptible. Within each cultivar, 1 to 10% of the plants were scored as resistant phenotypes. When ≈ 30% of leaf area was affected by Stemphylium leaf spot, forage yield was reduced up to 30%. Uninoculated regrowth from previously inoculated plants was also reduced up to 30%. Selection for resistance to this disease in red clover should result in the development of resistant germplasm and should improve forage yield of the species.