Rock phosphate-solubilizing Actinomycetes: screening for plant growth-promoting activities

Abstract

In order to select Actinobacteria that could improve plant growth and thus agricultural yield, we assessed different plant growth promoting (PGP) abilities of eight rock phosphate (RP)-solubilizing Actinomycete isolates originating from Moroccan phosphate mines. Six of these strains were able to grow on root exudates of the wheat plant as sole nutrient sources and were efficiently releasing soluble phosphate from RP. These strains also inhibited the growth of potentially phytopathogenic fungi, bacteria (Gram +/-) or yeasts. Five of these strains produced indoleacetic acid and four showed endophytic properties. When these strains were grown, in the presence of the wheat plant, in a synthetic minimum medium (SMM) containing insoluble RP as unique phosphate source or in soil experiment, the most active RP-solubilizing strains had the highest stimulatory effect on the production of plant biomass. The most efficient strain Streptomyces griseus-related strain (BH 7 ), stimulated aerial growth of the plant more than 70% in test tubes and more than 30% in RP soil compared to the non-inoculated control treatment. This study demonstrated that our selected Actinomycete strains could be used for the development of novel, non-polluting; farming practices by entering in the formulation of novel biofertilizer and biocontrol products constituted by spores and/or mycelium of the ad hoc Actinobacteria in association with pulverized RP.

Soil Properties Related to the Occurrence of Rock Phosphate-Solubilizing Bacteria in the Rhizosphere Soil of Faba Bean (Vicia faba L.) in Morocco

“…The most suitable medium for the enumeration of PSB is NBRIP [29] supplemented with 5 g L −1 rock-phosphate powder from the phosphate mine of Khouribga (RPK). The elemental analysis (%) of RPK was described earlier [30] and showed: O, 56.53%; F, 2.42%; Na, 1.81%; Mg, 1.94%; Al, 2.03%; P, 9.37%; S, 0.77%; Sn, 0.12%; Ca, 16.35%; Fe, 0.60%. Before use, the RPK was carefully washed with the extraction solution Mehlich 3 [31] and several times with hot distilled water to remove all traces of available P; then, it was autoclaved and added to the medium of sterile culture as the only source of P. The number of bacteria per gram of soil was determined by the standard method of colony forming unit (CFU) [19] after 3 days of incubation at 28 ± 2 • C. Both media were supplemented with 100 µg·mL −1 of cycloheximide to inhibit fungal growth.…”

In vitro Antimicrobial Assay of Actinomycetes in Rice AgainstXanthomonas oryzae pv. oryzicola and as Potential Plant Growth Promoter

“…Actinomycetes have been associated as biocontrol agent in several studies against plant pathogenic fungi and pathogenic bacteria (Hasegawa et al 2006;Baltz 2008;Loqman et al 2009;Oskay 2009). Apart from that, actinomycetes are also able to promote plant growth by the production of phytohormone and indole acetic acid compound (Hamdali et al 2008). However, potential of actinomycetes as plant growth promoter has been poorly investigated despite of their abundance population in soil microflora (Doumbou 2001).…”

Screening of cultivable endophytic bacterial isolates for their plant growth promoting activity in rice

“…Positive isolates resulted for increased root length and shoot length were analyzed for IAA production according to Hamdali et al (2008). Pink colour development in a solution indicated the presence of IAA Data regarding the parameters of seed germination such as root length (cm) and shoot length (cm) were collected and tabulated.…”