SCUTELLOSPORA-CALOSPORA (NICOL AND GERD) WALKER AND SANDERS ASSOCIATED WITH SUBTERRANEAN CLOVER - DYNAMICS OF COLONIZATION, SPORULATION AND SOLUBLE CARBOHYDRATES

Two time-course experiments were conducted to investigate the relationship between colonization and sporulation by Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders colonizing roots of subterranean clover (Trifolium subterraneum L.). The percentage of root length colonized by S. calospora increased up to 49 d in expt 1 and 32 d in expt 2 after which it declined. At this stage, there was no further increase in mycorrhizal root length but a sharp increase in non-mycorrhizal root length. In expt 1, the soluble carbohydrate concentration of the roots decreased during the first 49 d, followed by a sudden increase, coinciding with the decline in the percentage of root length colonized. One week before this the shoot P inflow also decreased. In both experiments, sporulation by S. calospora occurred after the decline in colonization. During sporulation there is no further spread in colonization within the root, which may result in increases in soluble carbohydrate concentration within the root. Spore formation may be aided by carbon stores located in the external auxiliary bodies formed by species of the genus Scutellospora.