Compatibility of Microbial Bioagents Singly and in Combinations Against Plant-Parasitic Nematodes Infesting Sweet Orange Trees and Effects on Non-Parasitic Nematodes (Fungivorous and Free-Living Species)

Four bioagents microbes were selected to assess effects singly and in combinations against plantparasitic nematodes (PPNs) and non-parasitic nematodes, in vitro and in vivo. Three of these microbes—Trichoderma asperellum, T. harzianum, and two strains of Pseudomonas fluorescens are widely utilized for nematode control, while the fourth, Rhodosporidium paludigenum as yeast, had not previously been tested against PPNs. The study evaluated the synergistic or antagonistic effects of these microbial mixtures. All combinations reduced PPN populations and increased other nematode species. Specifically, the mixture of R. paludigenum and T. harzianum was most effective against Tylenchulus semipenetrans, reducing its population by 68%, while T. asperellum combined with P. fluorescens strain 1 reduced Helicotylenchus spp. by 73.9%, and P. fluorescens strain 2 combined with R. paludigenum was most effective against Xiphinema spp., with a reduction of 67.2% after three months in the field. No reduction was observed in Tylenchus spp. and Rhabditis spp. These findings were corroborated by an in vitro experiment, where the mixture of R. paludigenum and T. harzianum deactivated the J2 stage of T. semipenetrans and reduced egg hatching by 63% and 20.6%, respectively, within four days of application. In conclusion, combining these tested microbes effectively reduces PPN populations in citrus without harming non-parasitic nematodes. It is recommended to incorporate these microbial mixtures with other biocontrol strategies to preserve soil health and reduce reliance on chemical nematicides in citrus groves.