IN VITRO BIOCONTROL POTENTIAL OF NATIVE PGPRS FROM COFFEA ARABICA RHIZOSPHERE AGAINST MELOIDOGYNE SPP. AND PHYTOPATHOGENIC FUNGI

Strategies for biological control of root-knot nematodes (RKN, Meloidogyne spp.), include the use of microorganisms, such as Plant Growth Promoting Rhizobacteria (PGPR), with a broad range of antagonistic activity against different phytopathogens. In this study we tested in vitro five PGPR isolates proceeding from the rhizosphere of coffee plants sampled at Villa Rica, Cerro de Pasco-Peru (Longitude W 75°17'25" Latitude S 10°45'12.2"). The trials included antagonism assays vs phytopathogenic fungi and RKN isolated from coffee roots. The isolates that displayed plant growth promotion and/or biocontrol capabilities were selected for molecular characterization, by sequencing their 16S rRNA ribosomal gene. Meloidogyne spp. identification was based on perineal patterns and molecular analysis of mtDNA, COII/16S and rDNA ribosomal genes, through PCR amplification with specific primers. Molecular characterization of isolates M3ACT14, M4ACT5 and M4ACT1 based on 16S rRNA gene sequences classified them within the genus Streptomyces, closely related to S. mirabilis (100%), S. humi (99.7%) and S. plumbiresistens (98.9%), respectively. Four PGPR isolates produced indolacetic acid, with highest production rates for M4ACT5 (10.4 ?g ml-1), M4ACT1 (8.8 ?g ml-1), and M4ACT7 (7 ?g ml-1). Two isolates were able to solubilize CaHPO4. Isolate M4ACT1 had higher rates of phosphate solubilization efficiency (27.1%, 15.8% and 33.9%) when incubated at 20, 28 and 35 °C, respectively. Dual cultures with M4ACT1 and M4ACT5 showed high antagonistic activity (% of in vitro growth inhibition) against Rhizoctonia sp. (40.9%, 40.9%), Fusarium sp. (40.3%, 41.1%) and Colletotrichum sp. (41.3, 49.2%), respectively. COII/16S and 18S sequences obtained from RKN populations 1, 2, and 5 showed 97, 93 and 83% identity with M. exigua, whereas PCR from population 6 (from chili roots), yielded a 18S rDNA gene sequence with a higher identity with M. arenaria, and the other populations gave undetermined amplicons. In vitro RKN antagonism assays, with population 1, showed a nematostatic effect (percent of immobilization) for M3ACT14 (100%), M4ACT5 (50.6%) and M4ACT7 (46.9%), all significantly higher compared to Triptic soy broth (TBS) (20.1%) and water (11.2%) controls, without inoculum (LSD test, P < 0.05). The nematicidal effect (mortality rate) was significantly higher for M3ACT14 (100%) and M4ACT7 (36.4%), compared to TBS (13.1%) and water (11.2%) controls (LSD test, P < 0.05). The selected PGPR showed a biocontrol potential for environment friendly management of Meloidogyne spp. and fungi on coffee. Further research is needed to develop appropriate field technologies for inoculation of infested roots and soil