EFFECT OF SOIL INOCULATION WITH VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI AND EITHER PHOSPHATE ROCK DISSOLVING BACTERIA OR THIOBACILLI ON DRY-MATTER PRODUCTION AND UPTAKE OF PHOSPHORUS BY TOMATO PLANTS

The effect of inoculating soil with phosphate rock dissolving bacteria (PRDB) or sulphur (S) oxidising micro-organisms on shoot dry matter (DM) production and phosphorus (P) uptake of a tomato cultivar (Lycopersicon esculentum Mill, Virosa NT2) colonised with the vesicular-arbuscular mycorrhizal (VAM) fungus Gigaspora margarita (Becker and Hall) was determined in a pot trial. Inoculation with PRDB did not affect shoot DM production and P uptake. Shoot DM and P uptake were also not increased when VAM and PRDB were inoculated together. PRDB were temporarily detrimental to shoot DM production. The PRDB population declined soon after soil inoculation but recovered after addition of a phosphate-free nutrient solution. It is suggested that soil bacteriostasis and a deficiency of easily metabolisable carbon compounds were the causes of the failure of the PRDB culture. Thiobacilli inoculation appeared to be detrimental to shoot DM production, and a combined inoculation of VAM and thiobacilli did not cause any significant increase in shoot DM. The resident thiobacilli were efficient S oxidisers and it is suggested that no inoculation of thiobacilli was required. The reasons for the adverse effects of thiobacilli inoculation are not known.