Transfer of phosphorus from Rhizoctonia solani to the mycoparasite Arthrobotrys oligospora

Abstract

Arthrobotrys oligospora parasitizes Rhizoctonia solani by coiling around the host hyphae and killing the cells under the coils and adjacent cells without penetrating the host cell wall. In experiments with one isolate of A. oligospora and one isolate of R. solani phosphorus was transferred from R. solani to A. oligospora during parasitism. In two double labelling experiments with 32 P-labelled R. solani mycelia and 33 P-labelled A. oligospora mycelia, 23 and 9%, respectively, of the phosphorus in the A. oligospora conidia formed during the interaction came from R. solani . Very little of the phosphorus from R. solani was transferred into the old mycelium formed before the interaction started. Conidiation and growth pattern differed to some extent between the two experiments. In experiment 2 more conidia were formed than in experiment 1 whereas A. oligospora hyphae invaded the area outside the interaction area (with coils) occupied by R. solani to a greater extent in experiment 1. However, both the size of the interaction area and the density of coils within this area were similar in both experiments. The usage of the available phosphorus in the interaction area was estimated to be 51 and 56%, in experiments 1 and 2 respectively. These estimates are conservative and the actual values might be closer to 100%. The experiments show that a non-penetrating mycoparasite can be a parasite in the strict sense since nutrients derived from the host hyphae made up a considerable proportion of the mycoparasite biomass formed during the interaction.