Paraconiothyrium: identification, biological control and tropical forage grass performance

Abstract

Endophytic fungi colonize living plant tissues, establishing mutualistic relationships and are also reported to are considered biological control agents and bioremediators. The aims of this study were to identify fungi of the genus Paraconiothyrium by morphology and using different molecular markers, to evaluate the inhibition of Sclerotinia sclerotiorum, the parasitism and inactivity of its sclerotia and to optimize a technique of inoculation of Brachiaria brizantha cv. Marandu and Panicum maximum cv. BRS Tamani seeds using endophytic fungi of the genus Paraconiothyrium to evaluate the germination of the inoculated seeds and the development of the plants from these seeds. Endophytic fungi isolated from forage grass were reactivated in PDA at 25ºC for 15 days. For sporulation, they were grown in different culture media and temperatures. Molecular identification was based on the analyzes of the ITS, LSU, γ-actin and β-tubulin regions. In vitro antagonism against S. sclerotiorum was performed and subsequently sclerotia were immersed in spore suspension of each endophytic fungus and distributed in Petri dishes on a substrate with germinating paper, moistened with sterile distilled water. The viability test of these parasitized sclerotia was performed on agar bromophenol medium (NEON). To evaluate whether the difference in the osmotic potential of the culture medium interfered with fungal mycelial growth, they were grown in modified PDA medium with four different mannitol concentrations (-0.6, -0.8, -1.0 and -1.2 MPa). It was evaluated the seeds germination of B. brizantha cv. Marandu and P. maximum cv. BRS Tamani and the development of the plants from these seeds inoculated with endophytic fungi of the genus Paraconiothyrium under normal conditions and under water stress. The fungi were identified as P. cyclothyrioides and P. estuarinum. All fungi inhibited the growth of S. sclerotiorum, in vitro, and parasitized their sclerotia, and four of these fungi were able to prevent these sclerotia. The highest osmotic potential (-1.2 MPa) was used because there was no significant difference between the different potentials tested. There was an increase in the number of germinated seeds, in relation to the control, inoculated with the fungi CML3697, CML3698 and CML3699 for Brachiaria and with the fungi CML3697 and CML3699 for Panicum. For Brachiaria, there was a gain of plant mass in the plants inoculated with fungi CML3695, CML3696 and CML3698, and for Panicum, in the plants inoculated with fungi CML3695, CML3698 and CML3699. Under water stress, there was an increase in the number of germinated seeds for both grasses, in relation to the experiment without water stress. Endophytic fungi of the genus Paraconiothyrium have potential in the biological control of S. sclerotiorum, and can stimulate the germination of forage seeds and the development of the plants from these inoculated seeds.