The role of pathogen suppression on the growth promotion of wheat by Penicillium radicum

The fungus Penicillium radicum can be used as an inoculant to promote the growth of wheat crops. Phosphate solubilisation by microorganisms has been suggested to be a major mechanism of plant growth promotion (PGP), but field trials and glasshouse trials with P. radicum have shown that other mechanisms are involved. This work tested the potential for biocontrol of soilborne plant pathogens as an alternative mechanism of PGP by P. radicum. In vitro, P. radicum significantly (P < 0.05) inhibited the growth of Gaeumannomyces graminis var. tritici (Ggt), Rhizoctonia solani, Pythium irregulare and Phytophthora cinnamomi but not the beneficial fungus Trichoderma koningii. Sterilised culture extracts of P. radicum contained inhibitory activity, suggesting production of antibiotic compounds. Subsequently, the effect of P. radicum on take-all disease of wheat was investigated in a series of glasshouse trials. In the first two experiments, P. radicum did not exhibit biological control activity against take-all disease, but rather increased disease severity (P = 0.02). Furthermore, PGP by P. radicum (21% increase in shoot dry weight; P = 0.001) was removed when inoculum of Ggt was added to soil. An experiment was conducted to investigate the interactions between the fungicide fluquinconazole (Jockey), the biocontrol agent T. koningii 7a and P. radicum on wheat growth in the presence of Ggt. All treatments significantly reduced take-all disease severity on wheat roots (P < 0.05), with the most effective treatment being P. radicum + Jockey (11% disease reduction). Similarly, dual inoculation with P. radicum + Jockey resulted in significantly higher shoot dry weights (31%; P < 0.05). The detrimental effect of take-all disease on PGP by P. radicum may explain some of the variability associated with the use of P. radicum in field situations. The integration of P. radicum with a chemical treatment for take-all control has shown excellent potential and could be used to increase the reliability and efficacy of P. radicum in situations of potential disease. © Australasian Plant Pathology Society 2006.S. A. Wakelin, S. T. Anstis, R. A. Warren, M. H. Ryde