English abstract
Plant growth in Oman is often reduced by P deficiency in soils. The purpose of this study was to determine how Tomato (Lycopersicon esculentum) plants are affected by inoculation with arbuscular mycorrhizal fungi (AMF) prepared as a commercial product by Mycoplant Company of Germany. The inoculum contained four species (strains) of the Glomus genus (G. mosseae, G. fasciculatum, G. intraradices and G. etunicatum) that were expected to colonize tomato roots and enhance P uptake. Tomato Plants (GS12 variety) were grown from seed in pots under shade. The experiment consisted of the following treatments; two nutrient-deficient, unsterilized soils (loamy sand and silt loam); three P fertilization rates (PFR) [i.e. 0, 75 (sub-optimal) and 150 (over-optimal) kg P/ha]; with and without addition of inoculum. Plant dry matter yield, nutrient content of leaves and mycorrhizae root colonization were assessed 100 days after sowing. All plants were mycorrhizal colonized irrespective of inoculation status or P fertilization rates. AMF inoculation significantly increased the colonization percentage (from 32 to 49% of total roots) in loamy sand and (from 32.67 to 44.67) in silt loam (p<0.05) when no P fertilizer was applied. Addition of P fertilizer reduced the colonization percentage in inoculated soil of both types, but had no effect on uninoculated soils in general. When no P was added to soil, inoculation significantly increased the dry matter, from 1.65 to 2.20 g/plant. Relative mycorrhizal dependency of inoculated plants was 33%. Enhancement in plant growth due to inoculation closely mirrored the increase in mycorrhizal colonization percentage (i.e. 49% compared to 32% for inoculated and uninoculated, respectively). In silt loam soil, no significant differences in dry matter were observed between inoculated and uninoculated plants grown at all three PFRs. Inoculated plants had significantly (p<0.05) higher concentrations of P in leaves than uninoculated plants. In loamy sand soil, inoculation did not lead to any significant increase in dry matter or leaf P concentration in plants grown with over-optimal PFR. Inoculation significantly decreased (p<0.05) plant growth when plants received sub optimal PFR (i.e. from 2.21 to 1.87 g/plant). The study showed that mycorrhizal fungi colonise tomato roots in two soils of contrasting texture and some improvement in dry matter yield and P status of plants can result from inoculation with effective strains from the Glomus genus. Further work is needed to optimise the growing conditions in Oman required for the expression of mycorrhizal colonisation of tomato plants by indigenous species, supplied in the form of effective inoculant.
