03583nam a2200205 a 450000100080000000500110000800800410001910000160006024500910007626000500016730000100021750000190022752030470024665000100329365000110330365000160331465000230333065000100335365000140336315593131999-11-04       1988    bl uuuu  m   00u1 u    #d1 aSANO, S. M.  aInteractions betweem Acaulospora laevis and glomus SP in the formation of mycorrhizas.  a[s.l.]: University of Western Australiac1988  a112p.  aMaster Thesis.  aMost agricultural soils contain several species of VA mycorrhizal fungi. The roots of plants grown in the field are usually colonized by more than one species of VA mycorrhizal fungus. In the early stages of plant growth, the percentage of root length colonized by each species of fungus is positively related to the number of propagules of that species present in the soil. For some species, the same number of propagules may produce a different percentage root length colonized according to soil conditions such as temperature, moisture and soil pH. These factors can affect spore germination and hyphal growth in the soil. Individual species of VA mycorrhizal fungi have also been found to have different responses to these conditions. In field soils where several species of VA mycorrhizal fungi are present it is unclear how the proportion and amount of root colonization by each fungus are controlled, and whether the percentage of root lenght colonized by one fungus is affected by the presence of other species. My hypothesis was that when more than one species of fungus is present in the soil the fungus that has the greatest amount of infective hyphae will colonize the greatest proportion of the roots. To test this hypothesis I inoculated two species of VA mycorrhizal fungi both separately and together, using different quantities of inocula is a soil with different quantities of lime added. I used Acaulospora laevis because germination of spore of this fungus has been shown to be decreased by increasing soil pH. I used Glomus sp. because in earlier studies infection by this fungus was not affected by pH. When the two species were inoculated together, I also studied the effect on root colonization by varying the placement of inoculum of Glomus sp. Adding lime increased soil pH, which decreased mycorrhizal formation by A laevis when inoculated alone but infection by Glomus sp. was lagerly unaffected A. laevis colonized the greatest percentage of the roots in an acid soil (pH 47, 1/5 w/v 0.01 McaCl2) while Glomus sp. colonized most of the roots in a neutral soil (pH 7.3) when both fungi were inoculated together. However at soil pH values ranging from 5.3 to 6.3 the amount of mycorrhizas formed by each fungus in the presence fo the other was related to the quantity of inoculum added. The method of placement of inoculum of Glomus sp. did not affect root colonization by A. laevis. However, in an acid soil, Glomus sp. colonized more roots in the presence of A. laevis when inoculum of Glomus sp. was banded than when inoculum was mixed throughout the soil; the reverse occurred in a neutral soil. I concluded that mycorrhizal formation by each fungus depended on the quantily of infective hyphae thath reached the roots at an early stage of plant growth. In this study, the effect of one species upon another was associated with the amount of infection formed by each fungus at an early stage, that is, the higher the root colonization by one species the greater the decrease in colonization by the other fungus.  afungi  aGlomus  amycorrhizae  aAcaulospora Laevis  aFungo  aMicorriza