Effects of phosphate solublizing rhizobacteria on growth and yield of Linseed crop in Jimma zone of Oromiya Region, South West Ethiopia

Abstract

Phosphorus deficiency is a major constraint in crop production, since some of the chemo-fertilizers applied formed insoluble Phosphate salts. Beneficial microbes of the soil can solublize these salts into bioavailable forms. This study was undertaken with the main objective of evaluating the effects of Phosphate solublizing bacteria on growth and yield of Linseed crop (Linum usitatissimum L). Thirty soil samples were collected aseptically from five linseed sites (farms) of Omonada district of Jimma zone, Oromiya region, South West Ethiopia. The soil samples were serially diluted up to (10-6) level, 0.1ml aliquot from each dilution was spread plated on solid Pikoviskaya’s agar. Some distinct countable colonies (10-20) of various colors and morphologies were isolated and tested for in vitro phosphate solublization potential on solid medium, were purified on sterile nutrient agar and characterized on the basis of morphological, biochemical and physiological features. A total of seventy six phosphate solubilizing bacteria were isolated from the collected soil samples. Six best phosphate solublizers were selected for further liquid media solublization test using National Botanical Research Institute for P broth media, two of the six selected isolates were also marked as prime HCN-producers. Finally, the six selected isolates were inoculated on two local linseed varieties under greenhouse condition and evaluated for their effects on linseed’s growth, yield and yield components. All isolates were identified following standard procedures, belonged to three main genera: 46 (60.5%) Pseudomonas, 18 (23.7%) Bacillus and 12 (15.8%) were Arthrobacter. The six isolates selected for greenhouse evaluation were: Pseudomonas (JURB3, JURB9, JURB11 and JURB21) and Bacilli (JURB50 and JURB57). Both genera inoculants resulted in significantly (p<0.05) higher growths in both “Romae” (V1) and “Shewa” (V2) local linseed varieties in terms of mean root length and mean shoot height of maximum (27.27- 69.7) % and 69 %, respectively. Similarly positive responses were recorded for dry weight (g) of roots and shoots. But the ratios of dry root to shoot were either significantly lower in some or similar in others with respect to controls. All treated linseeds of both V1 and V2 varieties with the selected inoculants responded significantly (p < 0.05) greater yield and yield components. Accordingly, inoculations with Pseudomonas resulted in higher (89-533%) seed weight, capsule number (68-200%) and mean P-uptake of (305.5-607.5%) as compared to controls. In conclusion, as both in vitro and in vivo evaluations confirmed, Bacillus and pseudomonas were dominant genera of Linseed rhizosphere and can be used as potential source of bio-inoculants.