Nutritional factors affecting the behaviour of Uromyces viciae‐fabae uredospores on broad bean leaves

Abstract

Both germination of Uromyces viciae‐fabae uredospores and growth of germ tubes were increased when spores were leached for 12 h at 0.4 ml/min water flow whereas leaching at aflow rate of 2.8 ml/min completely inhibited germination. Washing uredospores once in water caused a reduction in growth of germ tubes and in the numbers of lesions produced on detached leaves of the host, broad bean (Vicia faba).During germination uredospores from recently formed pustules leaked considerably moreendogenous nutrients on hydration than older uredospores. However, the majority of the leaked compounds were reabsorbed by young uredospores within a few hours. Concentrations ofglucose and leucine equivalents leaked from uredospores and from leaves were compared.Leaf leachates stimulated growth of uredospore germ tubes to an extent similar to that caused by low concentrations of glucose and amino acids but the addition of pollen inhibited growth of germ tubes. A variety of nutrients caused stimulation of uredospore germination and growth of germ tubes at low concentrations whereas higher concentrations of exogenous nutrients inhibited these processes. The response of uredospores was affected by their age.Utilization of exogenous 14C‐labelled nutrients by germinating uredospores was very low compared with that of cells of a leaf surface yeast, Cryptococcus sp. Cryptococcus; cells could consume over 90% of the glucose in a solution of glucose and amino acids of concentrations similar to those in leaf leachates before germinating U. viciae‐fabae uredospores had taken up 10%.