title: Rock phosphate solubilization and colonization of maize rhizosphere by wild and genetically modified strains of Penicillium rugulosum.
abstract: Maize root colonization and phosphate solubilizing activity of the fungus Penicillium rugulosum were assessed in a greenhouse trial using soil-plant microcosms. The bacterial gene hph conferring resistance to hygromicin B was introduced by electroporation in the wild-type strain IR-94MF1 of P. rugulosum and one transformant, w-T3, was selected. Maize plants were grown for 5 weeks in a P-poor soil and fertilized with a Florida apatite mineral, with Navay, an apatite rock deposit from Venezuela, or with simple superphosphate. Inoculation treatments included strain IR-94MF1, transformant w-T3 and two IR-94MF1 UV-induced mutants with enhanced (Mps++) or reduced (Mps-) in vitro mineral phosphate solubilizing activity. In the absence of P fertilization, inoculation with any P. rugulosum isolate significantly reduced the size of the total and P-solubilizing bacterial community present in maize rhizosphere. The bacterial community significantly increased in maize inoculated with IR-94MF1 and w-T3 when P was added as apatites Navay or Florida. All P. rugulosum strains were able to stimulate the growth of maize plants as indicated by 3.6 to 28.6% increases in dry matter yields. In the presence of rock phosphate, P uptake by maize plants inoculated with the two mutants Mps++ and Mps- was not always in agreement with their P-solubilizing phenotypes. Strain IR-94MF1 and transformant w-T3 increased P assimilation by the plants fertilized with Navay rock phosphate by 26 and 38%, respectively. In this treatment, w-T3 showed its highest significant maize rhizosphere colonization. With the simple superphosphate treatment, w-T3 increased P uptake in plants by 8% over the uninoculated control and also decreased significantly the community size of total bacteria, total fungi, and P-solubilizing fungi in the rhizosphere.
authors.affiliation: Département des Sols et de Génie Agro-alimentaire, Faculté des Sciences de l'Agriculture et de l'Alimentation, Pavillon Charles-Eugène-Marchand, Université Laval, Québec G1K 7P4, Canada.
authors.forename: I
authors.initials: I
authors.lastname: Reyes
authors.forename: L
authors.initials: L
authors.lastname: Bernier
authors.forename: H
authors.initials: H
authors.lastname: Antoun
mesh_terms: D001692:Biological Transport; D015169:Colony Count, Microbial; D018274:Electroporation; D005818:Genetic Engineering; D019015:Geologic Sediments / Q000737:chemistry*; D006921:Hygromycin B / Q000494:pharmacology; D008938:Mitosis; D009154:Mutation / Q000235:genetics; D010407:Penicillium / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics; D018517:Plant Roots / Q000166:cytology / Q000382:microbiology; D012988:Soil Microbiology; D012995:Solubility; D003313:Zea mays / Q000166:cytology / Q000382:microbiology*
chemical_list: D010710:Phosphates; D006921:Hygromycin B; D017853:Phosphotransferases (Alcohol Group Acceptor); C063242:hygromycin-B kinase