Winter injury and longevity in unselected clones from four wilt-resistant varieties of alfalfa

Small clones of unselected plants of four wilt-resistant varieties of alfalfa were grown in a nursery for 5 years with a cutting schedule and cultivation designed to favor longevity. Early in the fifth summer from a quarter to a half of the clones in these varieties were dead, and approximately half of the survivors were in poor condition. Although none of the winters through which the nursery had passed was regarded as severe, a few clones were winterkilled. Among the diseases present those which had selectively destroyed susceptible clones were bacterial wilt and downy mildew. These, together with winterkilling, appear to have killed only about half of the dead clones and to be responsible for but little of the poor condition in the living clones. The other parasitic diseases and injurious insects do not appear to have been sufficiently selective in their action to account for the death of clones or for the relatively poor condition of many of them. The deterioration and death of clones not accounted for by the diseases stated above appear to have had their origin in winter injury which differed greatly in character as well as extent in clones and in its consequences to the plants. In some cases, stunting of tops resulted, in others, reduction in the number of stems from killing of buds, with or without more or less extensive injury to the root, and decay of the crown. Infestation with leafhoppers and injury from fungus parasites are believed to have retarded the effectual repair of these injuries, but a critical examination of such relations must await the critical study of properly selected material. In the meantime it appears that winter injuries and their consequences in clones under field conditions can be recognized clearly enough to serve in the selection of strains of alfalfa with increased longevity, at least under the local conditions.