FUSARIUM SPP. AS ROOT PARASITES OF ALFALFA AND SWEET CLOVER IN ALBERTA

Abstract

Five pathogenic species predominated among the numerous isolates of Fusarium obtained from diseased roots of alfalfa and sweet clover in Alberta. Of these, the closely related species F. avenaceum (Fr.) Sacc. and F. arthrosporioides Sherb. appear most important, because they occur commonly and can cause serious injury to the roots, both in the early spring and during the growing season. F. culmorum (W.G.Sm.) Sacc. is very virulent during the summer, but is apparently non-pathogenic in the early spring. At both times F. Poae (Peck) Wr. and F. Scirpi Lamb, et Fautr. var. acuminatum (Ell. et Ev.) Wr. usually behave as weak pathogens. With the exception of F. avenaceum on alfalfa and sweet clover, and F. Scirpi var. acuminatum on alfalfa, these species have not been previously reported as occurring on the host plants indicated.Cardinal temperatures for growth in pure culture were:— F. avenaceum and F. arthrosporioides: − 2°, 24°, and 34 °C.; F. culmorum: 3°, 24° to 27°, and 34° to 36 °C.; F. Poae: −2°, 20° to 24°, and 32 °C.; F. Scirpi var. acuminatum: 1°, 24°, and 34 °C. All five species grew well at hydrogen ion concentrations ranging from pH 4.0 to 9.5. Carbon dioxide concentrations up to 20% had very little effect on the growth of F. avenaceum, F. arthrosporioides, or F. Poae, but the higher concentrations retarded the growth of F. culmorum and F. Scirpi var. acuminatum. The retarding effect of carbon dioxide was greater at 5 °C. than at room temperature.F. avenaceum produced more infection at temperatures up to 24 °C. than at 27 °C. At 27 °C., infection was much lighter in dry soil than in moist soil. F. culmorum caused severe damage at 18° to 27 °C., but did not attack the roots at low temperatures. F. avenaceum usually attacked roots of sweet clover more severely than those of alfalfa. All varieties of both hosts tested proved susceptible. In the absence of wounds, F. avenaceum readily entered roots through the basal tissues of branch roots, or through lenticels. Variant forms of this pathogen, which occurred frequently in pure culture, proved decidedly less pathogenic than the original isolates.Alfalfa and sweet clover roots were attacked by an isolate of F. avenaceum obtained from diseased roots of Vicia Americana, F. avenaceum, F. arthrosporioides, and F. culmorum from alfalfa and sweet clover proved pathogenic to roots of Trifolium spp. and to seedlings of wheat, oats, and barley. Certain isolates from the cereals were pathogenic to roots of alfalfa and sweet clover, and thus certain limits to crop rotation in reducing the root-rot damage caused by these pathogens are indicated.