INFLUENCE OF DIFFERENT P-SOURCES ON THE EFFICIENCY OF SEVERAL TROPICAL ENDOMYCORRHIZAL FUNGI IN PROMOTING THE GROWTH OF ZEA-MAYS L

The effect of inoculation with fourteen endomycorrhizal species belonging to the genera Gigaspora, Scutellospora, Glomus, Acaulospora and Entrophospora on the growth of maize (Zea mays L.) was evaluated under glasshouse conditions in an unsterilized tropical virgin soil using two P sources with different solubility. In both P treatments the population of indigenous mycorrhiza species was not affected and growth of maize was enhanced. Introducing VAM species additionally modified the growth pattern of maize. Using a low-grade rock phosphate (Patos de Minas) from Brazil all endophytes with exception of Gigaspora margarita, Scutellospora verrucosa, Scutellospora gregaria, Entrophospora colombiana and Glomus pallidum improved shoot dry weight. In the treatment with single superphosphate, dry matter production was not significantly enhanced by Gigaspora margarita, Gigaspora gigantea, Scutellospora verrucosa, Scutellospora reticulata, Scutellospora gilmorei and Glomus manihotis. When rock phosphate was added root fresh weights were enhanced only by three endophytes (Gigaspora margarita, Gigaspora gigantea and Acaulospora rehmii); with single superphosphate none had a significant effect. The percentage of P in shoots was almost equal in non-inoculated and inoculated plants and yield responses did not always follow the pattern of P uptake. Mycorrhizal root infection was always highest in the treatment with single superphosphate and in most cases a correlation with plant growth was found. The present results show that introduced vesicular arbuscular mycorrhiza species differently promote growth of maize according to their adaptability to the P source and to their capability to compete with native VAM endophytes.