In vitro inhibition of Phytophthora capsici, Fusarium oxisporum and Verticillium dalhiae by native plant growth promotion rhizobacteria strains from Mendoza

Abstract

The rapid growth of the human population and their need of food has impulse to extensive use of chemical fertilizers and pesticides to increase yield crop. These practices are costs and increase environmental pollution. In the last years, appear needs for novel agricultural practices that do not harm natural ecosystems. Different plant growth promotion Rhizobacteria (PGPR) have been studied and incorporated into agricultural practices and biocontrol has emerged in recent years as an alternative to pesticides. PGPR antagonize orprevent the effects of phytopathogens or deleterious microorganisms. PGPR produce substances that protect them against variousdiseases. Metabolites include hydrogen cyanide and antibiotics. Some strain PGPRs produce lytic enzymes as β-1,3-glucanase,chitinase, protease and cellulase that degrade the cell wall of fungi and produce a direct inhibitory effect on the growth of hyphae.Another important mechanism of biocontrol of PGPRs is related to the production of siderophores that chelate iron, making itunavailable to pathogens. In this study four native PGPR strains of Mendoza against pathogenic fungi of pepper crops were evaluated.The test was carried out by fourfold and repeated two times using independent Petri dishes for the growth of each bacterial strain andeach pathogens. On Luria Broth (LB) and potato dextrose agar (PDA) plates, one disc of a 5 mm plug carrying mycelia fungi (P.capsici, F. oxisporum or V. dalhiae) previously grown for 3 days in PDA was placed and each individual bacterium (60I1, 53F, 64S1,42P4) was plated as line. Bacterial strains were cultivated in LB medium for 24 h at 30 °C with orbital shaking (120 rpm). The bacterialcultures were adjusted to a final concentration of 108cells mL−1. The assay was performed incubated at 30 °C for 7 days. The myceliumgrowth was digitally determined every day. A control plate was included growing with the fungi. The percentage of inhibition was calculated comparing to the control. The strains 53F, 64S1 y 42P4 inhibited F. oxisporum and V. dalhiae in vitro mycelium growth.The 42P4 strain inhibited the P. capsici growth in APG plates. Also, we observed the production pyoverdine by 42P4 strain under UV in APG medium.