Effects of inoculation with strains of Rhizobium leguminosarum biovar trifolii on the growth of wheat in two different Morrocan soils

One hundred strains of Rhizobium leguminosarum bv. trifolii were isolated f rom roots of wheat cultivated in rotation with clover in two different regi ons of Morocco. The isolates were first screened for their effect on the gr owth of the cultivar Rihane of wheat cultivated in an agricultural soil und er greenhouse conditions. After 5 weeks of growth, 14 strains stimulating t he fresh or dry matter yield of shoots were selected and used in a second p ot inoculation trial performed with two different agricultural soils. The r esults show that the strains behaved differently according to the soil used . In the loamy sand Rabat, strain IAT 168 behaved potentially like a plant growth promoting rhizobacteria (PGPR), as indicated by the 24% increases (P < 0.1) observed in wheat shoot dry matter and grain yields. In the silty c lay Merchouch, no PGPR activity was observed, and 6 strains showed a signif icant deleterious effect on yields. These observations suggest that it is v ery important in a crop rotation system to choose a R. leguminosarum bv. tr ifolii strain that is effective with clover and shows PGPR activity with wh eat to avoid deleterious effects on wheat yields.